FI20185187A1 - A semiconductor package and a method of manufacturing a semiconductor package - Google Patents

Abstract

The present invention relates to a semiconductor package and a method for manufacturing a semiconductor package. The semiconductor package comprises a package body (300), at least one semiconductor die (200, 250) disposed within the package body (300) and a lead frame (100). The lead frame (100) is preferably manufactured from a planar sheet of metal, the sheet of metal defining a reference plane. The lead frame (100) comprises a die attach paddle (110) onto which the at least one semiconductor die (200, 250) is attached, a plurality of bond pads (120), and a plurality of leads (140) coupled to the plurality of bond pads (120). At least one additional support structure (150) extends from the lead frame (100) to the bottom surface of the package body (300), wherein the at least one support structure (150) is configured to form at least one solder area exposed at the bottom surface of the package body (150).

Description

A semiconductor package and a method of manufacturing a semiconductor package

Field

The present invention relates to a semiconductor package and a method to manufacture a semiconductor package. More particularly, the present invention relates to a semiconductor package with an improved structure that enables reduction of vibration of the semiconductor package and the semiconductors within the package due to external forces, and a method to manufacture such semiconductor package.

Background

Micro-Electro-Mechanical Systems, or MEMS can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have a mechanical functionality. Since MEMS devices are created with the same or similar tools used to create integrated circuits, micromachines and microelectronics can be fabricated on the same piece of silicon.

MEMS devices comprising structures can be applied to quickly and accurately detect very small changes in physical properties. For example, a microelectronic gyroscope can be applied to quickly and accurately detect very small angular displacements, and a microelectronic accelerometer can be applied to detect acceleration.

A MEMS device may be packed into a standard integrated circuit (IC) component package that is typically placed on a printed circuit board (PCB), into which it is attached by soldering.

Like any electronic devices, MEMS devices may be placed into various types of component packages. When the purpose of a MEMS device is to detect motion or posture, the component package comprising the MEMS device may be subject to harsh environment, in which the component

20185187 PRH 28 -02- 2018 package is subject to various external forces caused by linear acceleration, rotation and/or vibration, for example. Examples of such environmental conditions are vehicular installations and various industrial applications.

A problem caused by a mechanically harsh environment is that a component package soldered on a PCB may be caused to resonate at one or more frequencies. The resonance frequency depends on the physical dimensions of the component package as well as characteristics of the materials used in the package itself as well as materials used for attaching the component package to the PCB. At some frequencies, the legs of the component package may act as springs, causing the package to have some characteristic resonance frequencies on which the package tends to resonate with high gain. The problem is further increased by the requirement to have high Q-factors in the MEMS device packages.

This is because for being able to perform its intended task, the package of a MEMS device is not allowed to significantly dampen the mechanical signals that are to be detected by the MEMS die or dies disposed within the package. This causes the package resonance gain for a MEMS device package to be high by default.

Metal structures inside a component package that carry signals from the die to the outside are often referred to as lead frames. The die inside the component package is typically glued to the lead frame, and then bond wires electrically attach the die pads to the leads. The lead frame is then molded for example in a plastic or a ceramic case, and outside of the lead frame is cut-off, separating all leads.

Lead frames may be manufactured by removing material from a flat, planar plate of copper or copper-alloy. Common processes used for this are etching, which is particularly suitable for high density of leads, and

20185187 PRH 28 -02- 2018 stamping, which is suitable for low density of leads. The flat, patterned plate may further be pressed into a three-dimensional form, while the pressing force causes bending of selected parts of the lead frame.

Description of the related art

Exemplary traditional methods to reduce environmental stress on installed component packages are known as conformal coating and underfilling.

Conformal coating refers to a thin polymeric film which conforms to the contours of a PCB to protect the board's components. A conformal 10 coating acts as protection against harsh environments, for example moisture, dust, chemicals, temperature extremes and even mechanical protection. Assembly of conformal coating requires production process after soldering the components on the PCB, which process may comprise multiple phases. This increases production costs.

Underfilling refers to using an electrically-insulating adhesive under the component package. Underfilling improves both mechanical connection and heat bridge between the component and the underlying PCB, and reduces stress on solder joints. Underfilling may only be performed after the soldering process and, similarly to conformal coating, it requires 20 additional production process steps, which increases the production cost.

Patent US 9,691,688 discloses a thin plastic leadless package with an exposed metal die paddle. An exposed metal die paddle, referred in short as exposed paddle, is commonly used for transferring heat away from a packaged chip for example with quad-flat no-leads (QFN) type 25 component packages. For efficient heat transfer, a galvanic connection is expected between the exposed paddle of the component package and the PCB below it.

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However, it is sometimes not feasible to design a component package with an exposed paddle. An exposed paddle may cause problems by enabling moisture to enter into the critical parts of the semiconductor chips residing inside an exposed package. Moisture may cause problems 5 in both digital integrated dies and MEMS dies.

Patent US 7,642,638 discloses a semiconductor package with an inverted lead frame.

Some component designs require or prefer an inverted lead frame, in which the semiconductor dies are attached below the die attach paddle, 10 so that the semiconductor dies reside between the die attach paddle and the underlying PCB. Inverted lead frame design may be preferable for example for reducing torsion of a MEMS die caused by torsions of the component package. Torsion of a MEMS die might cause inaccuracy of MEMS detection results.

When an inverted lead frame is used, an exposed paddle is not available that may be joined with the PCB by soldering.

A solution is therefore needed for damping vibrations of an inverted lead frame component package without increasing cost in an assembly process when the component package is installed on a PCB. Although 20 the invented solution is particularly useful in a component package with an inverted lead frame, the solution may equally be utilized with a noninverted lead frame, when the die attach paddle itself is not exposed at the bottom face of the component package.

Summary

An object is to provide a semiconductor package and a method to manufacture a semiconductor package so as to solve the problem of damping vibrations of a component package. The objects of the present

20185187 PRH 28 -02- 2018 invention are achieved with the semiconductor package according to the characterizing portion of claim 1. The objects of the present invention are further achieved with the method of manufacturing a semiconductor package according to the characterizing portion of claim 9.

The preferred embodiments of the invention are disclosed in the dependent claims.

According to a first aspect, a semiconductor package is provided. The semiconductor package comprises a package body, at least one semiconductor die disposed within the package body and a lead frame 10 manufactured from a planar sheet of metal. The sheet of metal defines a reference plane. The lead frame comprises a die attach paddle onto which the at least one semiconductor die is attached, a plurality of bond pads, and a plurality of leads coupled to the plurality of bond pads. The leads are configured to provide connections between the at least one 15 semiconductor die and outside of the semiconductor package via bond wires coupling the at least one semiconductor die with the plurality of bond pads. The lead frame further comprises at least one additional support structure extending from the lead frame to the bottom surface of the package body, wherein the at least one support structure is 20 configured to form at least one solder area exposed at the bottom surface of the package body.

According to a second aspect, the at least one additional support structure comprises an arm and a handle. The arm is configured to extend from at least one other part of the lead frame. The arm couples 25 the handle to the at least one other part of the lead frame, and the handle is configured to have its bottom surface exposed at the bottom surface of the package body. At least part of the bottom surface of the handle is configured to form the solder area.

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According to a third aspect, the at last one additional support structure extends from any of the die attach paddle, at least one bond pad and at least one tie-bar of the lead frame.

According to a fourth aspect, the arm bent towards the bottom surface of the package body is configured to cause the handle to be disposed on a first plane parallel with the reference plane, wherein the first plane resides below the reference plane.

According to a fifth aspect, a layer of viscoelastic material is disposed 10 between the handle and the package body.

According to a sixth aspect, the solder area is formed by the entire exposed bottom surface of the handle, and wherein the solder area is attached to the arm via the handle.

According to a seventh aspect, the handle comprises a frame and a 15 central piece forming the solder area. The frame is attached to the arm and the central piece is attached to the frame and to the package body only by the layer of viscoelastic material.

According to an eighth aspect, the essentially planar die attach paddle is disposed at a second plane parallel to the reference.

According to a first method aspect, a method to manufacture a semiconductor package with a lead frame is provided. The method comprises patterning an essentially planar sheet of metal into the lead frame. The sheet of metal defines a reference plane. The lead frame comprises a die attach paddle coupled to the rest of lead frame with at least one tie-bar, a plurality of bond pads, a plurality of leads coupled to the bond pads, and at least one additional support structure. The

20185187 PRH 28 -02- 2018 method further comprises bending at least part of the at least one additional support structure below the reference plane, attaching at least one semiconductor die to the die attach paddle, bonding the at least one semiconductor die to a plurality of bond pads via a plurality of bond 5 wires and molding a package body using a mold. The die attach paddle, the at least one semiconductor die, and the plurality of bond pads are disposed entirely inside the package body, and the leads extend outside the package body. At least one solder area is formed at the bottom surface of the package body by at least part of the additional support 10 structure exposed at the bottom surface of the package body.

According to a second method aspect, the at least one additional support structure comprises an arm and a handle. The arm is configured to couple the at least part of the handle to the rest of the lead frame. The method further comprises exposing the solder area formed by the at 15 least part of the bottom surface of the handle at the bottom surface of the package body by cleaning the bottom surfaces by any of chemical deflashing, electrolytic deflashing, plasma etching and grinding.

According to a third method aspect, the patterning comprises extending the at last one additional support structure from any of the die attach 20 paddle, at least one bond pad and at least one tie-bar of the lead frame.

According to a fourth method aspect, the method further comprises covering the handle with a layer of viscoelastic material prior to molding the package body.

According to a fifth method aspect, the step of exposing comprises 25 cleaning the layer of viscoelastic material away from the bottom surface of the handle for forming the solder area from at least part of the bottom surface of the handle.

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According to a sixth method aspect, the handle comprises a frame and a central piece coupled to the frame with a plurality of thin metal bridges. The layer of viscoelastic material essentially fills the gap between the frame and the central piece. The step of exposing comprises grinding the 5 bottom surface of the package body and the bottom surface of the handle so that the thin metal bridges are removed by the grinding, so that the frame remains attached with the arm and the central piece forming the solder area is attached to the frame and to the package body only by the layer of viscoelastic material.

According to a sixth method aspect, the method further comprises bending the tie-bars so that the essentially planar die attach paddle is disposed at a second plane parallel to the reference plane.

According to another aspect, the lead frame is an inverted lead frame.

The present invention is based on the idea of forming additional support 15 structures in a lead frame. The additional support structures are particularly beneficial with an inverted lead frame, but similar structures may also be applied to a standard, non-inverted lead frame. The additional support structures extend to the face of the component package that faces towards a printed circuit board onto which the 20 component package is to be assembled. The additional support structures thus allow mechanically coupling the component package to pads provided on a PCB during assembly of the component package on the PCB. Some embodiments also allow electrically coupling of at least part of the lead frame to a set electrical potential, preferably a DC 25 potential, and more preferably to ground potential.

The present invention has the advantage that a component package with additional support structures according to the invention may be assembled onto a PCB without any extra assembly steps. Vibrations of

20185187 PRH 28 -02- 2018 the component package may be dampened simply by joining the additional support structures of the component package to the underlying printed circuit board simultaneously with joining the component leads during the same soldering process phases. Thus, cost 5 of assembly process is reduced. On the other hand, dampening the vibrations of the component package help to reduce errors in detection of physical phenomenon detected with a MEMS die within the component package caused by unwanted vibrations of the package. Thus, the invention improves reliability and accuracy of detection of a MEMS die.

Further, the invention may improve stability and achievable lifetime of the MEMS die within the component package, since vibrations of the component package could even damage moveable structures of the MEMS die.

Brief description of the drawings

In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawings, in which

Figure la shows a perspective view of a lead frame according to a first embodiment.

Figure lb illustrates an enlarged view of a part of the figure la.

Figure 2a illustrates a perspective view of a lead frame according to a second embodiment.

Figure 2b illustrates an enlarged view of a part of the figure 2a.

Figure 3a illustrates a perspective view of lead frame according to a third 25 embodiment.

Figure 3b illustrates an enlarged view of a part of the figure 3a.

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Figure 4 illustrates a perspective view of the lead frame after installation of at least one semiconductor die.

Figure 5 illustrates a bottom view of the result of the molding phase.

Figure 6 illustrates a cross-section of the component package after the 5 molding phase

Figure 7 illustrates a perspective view of the component package before the external parts of the lead frame are removed

Figure 8 illustrates a perspective view of a finished component package.

Figure 9 illustrates a perspective view of a finished component package.

Figure 10 illustrates a cross-section of a component package.

Figure 11 illustrates a perspective view of lead frame according to a fourth embodiment.

Figure 12 illustrates a transparent perspective view of the fourth embodiment.

The figure 13 illustrates a perspective view of a component package according to the fourth embodiment.

Figure 14 illustrates a schematic cross-section of a component package according to the fourth embodiment.

Figure 15 illustrates a part of a lead frame according to a fifth 20 embodiment.

Figure 16 illustrates a second perspective view of the lead frame for the component package according to the fifth embodiment

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Figure 17 illustrates a perspective view of the component package according to the fifth embodiment after molding.

Figure 18 illustrates a cross-section of the component package of the fifth embodiment.

Figure 19 illustrates a first perspective view of a component package according to the fifth embodiment.

Figure 20 illustrates a second perspective view of a component package according to the fifth embodiment.

Figure 21 illustrates a cross-section of a component package according 10 to the fifth embodiment.

Detailed description

For purposes of explaining the assembly process of the semiconductor package, we will define that terms such as up and above refer to a direction parallel to the positive z-axis marked in the figures, whereas 15 terms such as down, below and under refer to a direction parallel to the negative z-axis. It should be noticed, however, that in the figures la to lb, 2a to 2b, 3a to 3b, 4, 6 to 9, 11 to 13 and 16 to 20, the die attach paddle is upside down when compared to the intended orientation of the component package when assembled on a PCB, as illustrated with the 20 marked coordinate axes shown next to the figures. When the semiconductor package is assembled on a PCB, the negative z-axis will point towards the PCB onto which the component package is assembled preferably by soldering.

The figure la shows a perspective view of a lead frame 100 according to 25 a first embodiment. In this exemplary embodiment, the lead frame 100 initially comprises not only the parts that will be part of the final semiconductor package, but some parts of the lead frame, which we call

20185187 PRH 28 -02- 2018 external parts 101, that remain external of the semiconductor package will be cut off during the manufacturing process. A typical lead frame is manufactured by patterning an initially planar sheet of metal.

The lead frame comprises a plurality of leads 140 and bond pads 120. 5 The bond pads 120 will remain inside the semiconductor package and serve as contacts for bond wires, which are used for electrically coupling signals from one or more dies to the outside by the connection via the bond pad 120 and the respective lead 140. The leads 140 remain outside the finished semiconductor package and provide electrical 10 connections towards external circuitry. Thus, although the leads 140 are intended to remain outside the finished semiconductor package, they are not part of the external parts 101 of the lead frame 100 that will eventually be cut off.

The lead frame 100 of figure la comprises also a die attach paddle 110 15 onto which at least one semiconductor die may be attached to. At least one semiconductor die may for example be glued to the die attach paddle 110 with electrically non-conductive material. Thus, the at least one semiconductor die is mechanically attached to the die attach paddle, but not typically not electrically connected by the attaching. The die 20 attach paddle 110 may be attached to the rest of the lead frame with one or more tie-bars 130. The tie-bars 130 are configured to hold the die attach paddle 110 in its intended position during manufacturing process of the component package by coupling the die attach paddle 110 with the external parts 101. As shown in this embodiment, the tie25 bars 130 may be bent three-dimensionally in the manufacturing process so that the essentially planar die attach paddle 110 becomes disposed above a reference plane formed by the original, patterned and planar sheet of metal forming the lead frame 100. Alternatively, the tie-bars 130 may be bent so that the die attach paddle 110 becomes disposed

20185187 PRH 28 -02- 2018 below the reference plane, but pending the tie-bars 130 is not necessary, and the die attach paddle 110 may also reside at the reference plane. The reference plane may also be referred to as the plane of the lead frame or as the xy-plane. The plane of the die attach 5 paddle 110 is preferably parallel to the reference plane. If the tie-bars 130 are not bent, the die-attach paddle 110 may be coplanar with the reference plane. The essentially planar bond pads typically remain on the reference plane even in the final product. Thus, the reference plane originally defined by the planar metal sheet is also equivalent to the 10 plane defined by the bond pads, except in the rare case when at least some of the bond pads are bent to a different plane.

The lead frame comprises a plurality of additional support structures 150. In this first embodiment, two additional support structures 150 extend from the die attach paddle 110. The additional support structures 15 150 are bent so that they reach at least a first predefined level below the reference plane.

The lead frame 100 may be an inverted lead frame. The term inverted lead frame refers to a structure in which the lead frame 100 and particularly the die attach paddle 110 is configured to reside on the 20 opposite side of the semiconductor dies compared to a PCB onto which the semiconductor package is configured to be assembled. In other words, the semiconductor dies are configured to be disposed under the die attach paddle 110, and, when installed, the semiconductor dies will be disposed between the die attach paddle 110 and a PCB onto which 25 the component package is to be assembled for example by soldering.

Alternatively, the lead frame 100 may be a normal lead frame, in which the die attach paddle 110 resides under the semiconductor dies attached to it. In the given examples, the lead frame is illustrated as an inverted lead frame, since a non-inverted lead frame has also other known

20185187 PRH 28 -02- 2018 possibilities to implement mechanical support for the component package, such as exposed paddle.

The figure lb illustrates an enlarged view of the area in the figure la marked with a dashed rectangle, and particularly shows one of the 5 additional support structures 150 of the figure la. The additional support structures 150 of the figure la comprise an arm 151 and a handle 152. The arm 151 is configured to adjust the vertical level of the handle 152 with respect to the reference plane so that the handle 152 resides below the reference plane. The upper surface of the handle 152 preferably 10 forms a plane that is essentially parallel with the reference plane.

Alternatively, the upper surface of the handle may be for example curved.

The figure 2a illustrates a perspective view of a lead frame 100 according to a second embodiment. Similar to the first embodiment, the 15 lead frame 100 comprises a plurality of leads 140 and bond pads 120, a die attach paddle 110, tie-bars 130 and a plurality of additional support structures 150. In the second embodiment, two additional support structures 150 are attached to the tie-bars 130. The additional support structures 150 are bent so that they reach at least the first predefined 20 level that is below the reference plane.

The figure 2b illustrates an enlarged view of the area in the figure 2a marked with a dashed rectangle, and particularly shows one of the additional support structures 150 of the figure 2a. Similar to the first embodiment, the additional support structures 150 of the figure 2a 25 comprise an arm 151 and a handle 152. The arm 151 is configured to adjust the vertical level of the handle 152 with respect to the reference plane. The bottom surface of the handle 152 preferably forms a plane that is essentially parallel with the reference plane. Alternatively, the

20185187 PRH 28 -02- 2018 bottom surface of the handle 152 may be for example curved. This bottom surface eventually forms a solder area.

The figure 3a illustrates a perspective view of lead frame 100 according to a third embodiment. Similar to the first embodiment, the lead frame 5 100 comprises a plurality of leads 140 and bond pads 120, a die attach paddle 110, tie-bars 130 and a plurality of additional support structures 150. In the third embodiment, two additional support structures 150 are attached to the bond pads 120. The additional support structures 150 are bent so that they reach at least the first predefined level that is 10 below the reference plane.

The figure 3b illustrates an enlarged view of the area in the figure 3a marked with a dashed rectangle, and particularly shows one of the additional support structures 150 of the figure 3a. Similar to the first and second embodiments, the additional support structures 150 of the figure 15 3a comprise an arm 151 and a handle 152. The arm 151 is configured to adjust the vertical level of the handle 152 with respect to the reference plane. The bottom surface of the handle 152 preferably forms a plane that is essentially parallel with the reference plane. Alternatively, the bottom surface of the handle 152 may be for example curved. This 20 bottom surface of the handle eventually forms a solder area.

Figures 4 to 8 illustrate further phases of manufacturing a component package according to the invention. In these figures, the lead frame 100 of the first embodiment is used as an example, but the same phases apply also if the lead frame 100 of the second embodiment or the third 25 embodiment was used.

The figure 4 illustrates a perspective view of the lead frame 100 after installation of at least one semiconductor die. When an inverted lead frame is used, the semiconductor dies are disposed under the die attach

20185187 PRH 28 -02- 2018 paddle 110. If a non-inverted lead frame was used, the semiconductor dies would be attached above of the die attach paddle 110. In this embodiment, there are two semiconductor dies: a MEMS die 200 and a digital die 250. We may refer to these jointly as the semiconductor dies 5 or in short just as the dies. Any number of semiconductor dies may be installed according to the design of the device. Electrical connections are provided to the dies 200, 250 via bond wires 125. A bond wire 125 may be configured to couple between chip pads of two different semiconductor dies, or it may be configured to couple a chip pad of a 10 semiconductor die with a bond pad 120.

In a phase called molding, a mold is disposed on the lead frame 100 so that the internal parts the of the lead frame 100, such as the die attach paddle 110, the bond pads 120 and the additional support structures 150 as well as majority of the tie-bars 130, remain inside the mold, and 15 the volume defined by the mold is filled with molding material, for example with a plastic resin. The external part 101 of the lead frame 100 remains outside the mold. The molding material closes the internal parts within the volume of the mold, which defines the package body.

Figure 5 illustrates a bottom (xy-plane) view of the result of the molding 20 phase, indicating the outline of the package body 300. The package body 300 covers the die attach paddle 110, the dies 200, 250, the additional support structures 150 and the bond pads 120. The leads 140 remain outside the package body 300 as well as the external part 101. The tie-bars 130 remain also mainly within the package body 300, but 25 minor part of the tie-bars remains outside the package body 300, allowing the outside of the lead frame to be easily cut off later on. The bottom face of the package body refers to the face of the package body configured to be facing a printed circuit board onto which the semiconductor package is assembled for example by soldering.

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Figure 6 illustrates a yz-plane cross-section of the component package after the molding phase seen from the direction of the x-axis. The die attach paddle 110, the semiconductor dies 200, 250, the bond wires 125, the tie-bars 130 and the bond pads 120 now all reside inside the 5 package body 300 in the vertical (z-axis) dimension. The additional support structures 150 resides mainly inside the package body 300 as well: the arms 151 are disposed inside the package body 300, but the bottom surfaces of the handles 152 may be exposed at the bottom surface of the package body 300. The bottom face of the package body 10 and the bottom surfaces of the handles are configured to be facing a printed circuit board onto which the semiconductor package is assembled for example by soldering. This figure also demonstrates a benefit provided by bending the tie-bars 130, in order to move the die attach paddle 110 above the reference plane formed by the lead frame 15 100 in an inverted lead frame. By moving the die attach paddle 110 upwards by bending the tie-bars 130, the volume available within the semiconductor package body may be increased, since the distance between the die attach paddle 110 and the bottom surface of a package body increases. The increased distance allows for example installing 20 thicker semiconductor dies on the die attach paddle 110 inside the package body 300. Likewise, in a non-inverted lead frame, bending the die attach paddle 110 downwards increases the volume available within the semiconductor package body above the die attach paddle 110.

In some cases, the bottom surface of the handle 152 may not be fully 25 exposed at the surface of the package body 300 after the molding. For example, a small amount of molding material may cover the bottom surface of the handle 152 at least partially. In such case, the surface of the handle 152 intended to be exposed at the bottom face of the package body 300 may be cleaned for example with chemical or

20185187 PRH 28 -02- 2018 electrolytic deflashing, plasma or by mechanical grinding or polishing, for example.

The height of the additional support structure may be initially made slightly more than the vertical height of the upper mold's inner surface. 5 This way the additional support structure 150 may be caused to receive extra compressive force from the mold when disposed inside the mold. The extra compressive force beneficially reduces amount of unwanted mold material between the mold and the additional support structure 150, especially the handle 152. Thus, the bottom surface of the handle 10 152 remains more likely visible at the surface of the molded component package, and for example extra cleaning step for exposing the handle may be avoided.

Figure 7 illustrates a perspective view of the component package before the external parts 101 of the lead frame are removed. The leads 140 15 remain outside the package body 300, and the metal bottom surfaces of the handles are exposed at the bottom face of the package body 300, thus forming solder areas 154 which may be soldered for example to a PCB on which the component package is eventually assembled.

Figure 8 illustrates a perspective view of a finished component package 20 according to the first, embodiment. A finished component packages according to the second and third embodiments are in principle similar. The number, size, form, placement of the exposed bottom surfaces of the handles 152 at the bottom surface of the package body 300 may vary within and between the different embodiments. All other external 25 parts of the lead frame are now cut off, leaving just the leads 140 in place. The leads 140 are separated and bent downwards to their final form. A small cross-section of tie-bars 130 may be visible on the outer surface of the package body 300. The package is designed to be

20185187 PRH 28 -02- 2018 assembled in an inverted position, so that the bottom surfaces of the handles forming solder areas 154 are exposed at the bottom surface of the package body 300 configured to reside towards a printed circuit board (PCB) onto which the component package is configured to be 5 soldered. Thus, the component package is to be installed in an inverted position so that the negative z-axis points towards the PCB. The solder areas 153 are configured to be soldered to the underlying PCB.

When the component package is only soldered from the leads, the leads may mechanically act like a set of springs, which may allow the 10 component package, especially the package body to vibrate. This tendency of vibration may have certain resonance frequencies at which the vibration is especially strong. Soldering the solder areas 154, in other words the exposed bottom surfaces of the handles to the PCB, and thus attaching the additional support structures to the PCB, facilitate 15 reducing of vibrations of the component package. One example of such leaded package type is that of the disclosed embodiments, known as a small outline integrated circuit (SOIC). However, any package type with solderable leads and a plastic, ceramic or glass package body is equally applicable. Examples of applicable packages are for example plastic 20 leaded chip carrier (PLCC), and different types of quad flat packages (xQFP).

Figure 9 illustrates a perspective view of a finished component package according to the first embodiment. The component package similar to that of the figure 7, but the illustration shows also internal elements 25 residing within the molded component package body 300.

Figure 10 illustrates a schematic cross-section of a component package according to the first embodiment when installed on a printed circuit board 700. In the final phases of the manufacturing, the external parts

20185187 PRH 28 -02- 2018 of the lead frame are cut off except for the leads 140, and the leads 140 are bent to allow contact between the leads 140 and the underlying PCB 700. The component body 300 of this embodiment is installed in an inverted position, where the semiconductor dies, for example the digital 5 die 250 and the MEMS die 200 are disposed under the die attach paddle 110, in other words between the die attach paddle 110 and the PCB 700. Electrical contacts are provided between the leads 140 and the semiconductor dies by bond wires 125 coupling chip pads of the semiconductor dies via the bond pads 120 to the leads 140. The leads 10 140 (also known as legs) of the component package are bent towards the face of the component package configured to be facing towards the PCB 700 to allow coupling the leads 140 to the PCB 700 for example by soldering. The solder areas 154 are exposed at the bottom surface of the component body so that they may be coupled to the PCB 700 15 simultaneously with the leads 140. The solder material 710 may thus be configured to form a pattern which couples both the leads 140 and the solder areas 154 of the additional support structure to the PCB 700. The arms 151 of the additional support structure couple the handles 152 with the die attach paddle 110. As earlier illustrated, in other embodiments, 20 the additional support structure may be attached for example with one or more bond pads 120 or with tie-bars 130.

The solder areas 154 and thus the additional support structures may be coupled to any electrical potential on the PCB 700. Preferably the solder areas 154 are coupled to a DC potential, such as ground potential. The 25 solder areas 154 are galvanically and electrically coupled inside the package body 300 with the die attach paddle 110 either via the handle and the arm of the additional support structure, via tie-bars 130 or via solder pads 120. The die attach paddle 110 may thus be coupled through the solder areas 154 to any electrical potential. One possibility is

20185187 PRH 28 -02- 2018 to couple the die attach paddle to ground potential. A die attach paddle 110 may provide EMC protection for the semiconductor dies.

Figure 11 illustrates a perspective view of lead frame according to a fourth embodiment. In this embodiment, at least part of the additional 5 support structures, preferably at least the handles 152 thereof are covered with viscoelastic material 155, such as a synthetic or natural polymer, or a mixture thereof, before the lead frame is molded. The viscoelastic material 155 may be dispensed for example by dipping the additional support structures into liquid material, by laminating, by 10 lithography and so on. Viscoelastic material 155 may be applied to at least one of the additional support structures in any of the first, second and third embodiments, independent on the point of attachment between in the lead frame and the additional support structures. The viscoelastic material 155 may be dispensed before bending the 15 additional support structures or later. Preferably the viscoelastic material 155 is dispensed at least on the handles 152 so that the handles are entirely covered by the viscoelastic material 155 on all open faces. For ensuring proper coverage of the handles 152, the layer of viscoelastic material 155 may also partially cover the arm 151.

After dispensing the viscoelastic material 155, the bottom faces of the handles 152 intended to be exposed at the bottom face of the component package body may be cleaned in many different phases of the manufacturing process. The bottom faces of the handles 152 may be cleaned before molding, either before assembling the semiconductor 25 dies or after assembling of the semiconductor dies, or only after molding the package body. If the bottom faces of the handles 152 were cleaned from the viscoelastic material 155 before molding, this may be performed for example by grinding or by photolithography.

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Figure 12 illustrates a transparent perspective view of the fourth embodiment illustrated in the figure 11 after molding the component body 300. The handles 152 are exposed at the bottom surface of the component body 300. If the viscoelastic material 155 was not already 5 removed before molding from the bottom face of the handles 152, the viscoelastic material may surround the handles 152 on all sides. The viscoelastic material may be removed from the bottom face of the handles 152 in order to expose the leadframe metal intended to form the solder areas. This cleaning of the solder areas may be performed by 10 any of chemical or electrolytic deflashing, by plasma etching or by grinding the bottom surface of the component body 300.

The figure 13 illustrates a perspective view of a component package according to the fourth embodiment after cleaning the bottom surface of the component body 300. The solder areas 154, in other words the 15 bottom surfaces of the handles, are exposed at the bottom surface of the package body 300, and a thin layer of vibration suppressing viscoelastic material 155 is disposed between the handles and the component body 300. The additional support structure and its solder areas 153 are now ready to be used for coupling the component body 20 with a PCB. In the final steps of manufacturing, external parts 101 of the lead frame 100 are removed except the leads 140, and the leads 140 are bent towards the bottom of the component package.

Figure 14 illustrates a schematic cross-section of a component package according to the fourth embodiment when installed on a printed circuit 25 board 700. The component body 300 is installed in an inverted position, where the semiconductor dies, for example the digital die 250 and the MEMS die 200 are disposed under the die attach paddle 110, in other words between the die attach paddle 110 and the PCB 700. Electrical contacts are provided between the leads 140 and the semiconductor

20185187 PRH 28 -02- 2018 dies by bond wires 125 coupling chip pads of the semiconductor dies via the bond pads 120 to the leads 140. The leads 140 of the component package are bent towards the bottom of the component package configured to be facing towards the PCB 700 to allow coupling the leads 5 140 to the PCB 700 for example by soldering. Solder areas 154 are exposed at the bottom surface of the component body so that the solder areas 154 may be coupled to the PCB 700 simultaneously with the leads 140. A patterned layer of solder material 710 couples both the leads 140 and the solder areas 154 of the handles 152 of the additional support 10 structure to the PCB 700. The arms 151 of the additional support structure couple the handles 152 with the die attach paddle 110. Viscoelastic material 155 is disposed between the handle 152 and the component body 300.

Figure 15 illustrates a part of a lead frame 100 according to a fifth 15 embodiment. The figure 15 shows a perspective view of the lead frame 100 from above the reference plane to properly illustrate the additional support structures. In this example, the additional support structures are coupled to the die attach paddle 110, but they could as well be coupled to other parts of the leadframe 100 which are configured to be disposed 20 inside the component body after molding, such as the tie-bars 130 or the bond pads 120. In this embodiment, each handle 152 of the support structure has a frame 153 and a central piece 254, joined together with a plurality of bridges 156. The handle 152 is essentially planar. Thus, the frame 153 and the central piece 254 are preferably mutually coplanar, 25 and, similar to all other embodiments, the plane formed by the handle 152 formed by the frame 153 and the central piece 254 is preferably parallel to the reference plane. In this example, the frame 153 is a rectangle, but the frame may have any other form, for example annular. Likewise, the central piece 254 is in this example a square, but it may

20185187 PRH 28 -02- 2018 have any form, for example a circle. The bridges 156 between the frame 153 and the central piece 254 may be bent downwards (towards the negative z-axis) so that they essentially form an arc below the plane formed by the frame 153 and the central piece 254, or they may be 5 made thinner by grinding or pressing the material of the lead frame metal sheet into an arc shape that essentially resides between the upper and lower surfaces of the handle 152 so that the thickness of the bridges 156 is only a fraction of the thickness of the lead frame metal sheet in any other part of the handle 152. The middle, thin section of the arc 10 should be facing the bottom surface of the handle 152. The arc form facilitates removal of the bridges in a later phase.

Figure 16 illustrates a second perspective view of the lead frame 100 for the component package according to the fifth embodiment. This view shows the essentially flat bottom plane (xy-plane towards negative z15 axis) formed by the handles, with free space between the frame 153 and the central piece 254.

The handles 152 according to the fifth embodiment are covered with viscoelastic material 155 in the similar manner to the above described phase with figure 10. After applying the viscoelastic material 155, all 20 parts of the handle are preferably covered with the viscoelastic material 155, and also the entire volume in the handle between the frame 153 and the central piece 254 is filled with the viscoelastic material 155. In one variation of the method, the bottom surface of the frames 153 and the central piece 254 may be cleaned only after molding. In an 25 alternative variation, the bottom surface of the frames 153 and the central pieces 254 may be cleaned from the viscoelastic material 155 before molding the component body.

20185187 PRH 28 -02- 2018

Figure 17 illustrates a perspective view of the component package according to the fifth embodiment after molding. In this figure, semiconductor dies and bond wires are omitted for simplicity. If the viscoelastic material 155 was not removed from the bottom surface of 5 the handles 152 before molding, the handles 152 exposed at the bottom surface of the package body 300 are covered with a layer of the viscoelastic material 155. The external parts 101 of the lead frame are still attached to the component body.

Figure 18 illustrates a cross-section of the component package of the 10 fifth embodiment along the xz-plane after molding the component body 300. Semiconductor dies and bond wires are omitted for simplicity, but in a real product, dies would be attached to the die attach paddle and wire bonded prior to molding. The handles 152, each comprising the frame, the central piece, and a plurality of bridges, are disposed towards 15 the bottom face of the component body 300. If the bottom surface of the handles 152 were not cleaned before molding, the frames, the solder areas, and the bridges may still be covered with a layer of viscoelastic material. The bottom surface of the layer of viscoelastic material 155 covering the handle 152 may slightly bulge below the bottom surface of 20 the component body 300. By allowing slight bulging of the additional support structure ensures that the bottom surface of the handle 152 itself is coplanar or slightly below the bottom surface of the component body 300. Alternatively, if the viscoelastic material was removed from the bottom surface of the handle 152 before molding, the metal material 25 of the frame, the central piece and the bridges may be already exposed at the bottom surface of the component body.

Figure 19 illustrates a first perspective view of a component package according to the fifth embodiment after the bottom surface has been cleaned. The bottom face of the handles, comprising the bottom face of

20185187 PRH 28 -02- 2018 the frame 153, the central piece 254 and the bridges 156, is visible at the bottom face of the component body 300. A thin layer of the viscoelastic material 155 shows at the bottom face of the component body 300, while the layer of viscoelastic material 155 is disposed 5 between the frame 153 and the component body 300 so that they are not in direct contact with each other. The volume between the frame 153 and the central piece 254 is filled with viscoelastic material 155.

Figure 20 illustrates a second perspective view of a component package according to the fifth embodiment after the bottom surface of the 10 component body 300 has been further cleaned by grinding the bottom face of the package body 300 and the handle to a depth that causes the bridges between frames 153 and the central pieces 254 to become essentially removed. Now the central pieces 254 are only mechanically connected with the component body 300 via the viscoelastic material 15 155, while the frames 153 remain coupled with the lead frame 100 via the arms 151. Thus, there frame is also electrically coupled to the lead frame 100 via the arms 151. In this embodiment, the bottom surfaces of the central pieces 254 may form the solder areas. Due to grinding, also a minor part of the arm 151 may be exposed at the bottom surface of 20 the package body 300. The additional support structure is now configured for coupling the package body 300 mechanically to a PCB. In the final steps of manufacturing, external parts 101 of the lead frame not intended to be part of the final component package are removed, leaving only the leads 140 in place, and the leads 140 are bent towards 25 the bottom of the component package.

Figure 21 illustrates a schematic cross-section of a component package according to the fifth embodiment when installed on a printed circuit board 700. In the fifth embodiment, the arms 151 of the additional support structure couple the frames 153 of the handle 152 with the die attach paddle 110. Viscoelastic material 155 is disposed between the frames 153 and the central pieces 254 with the solder areas 154, as well as between the frames 153 and the component body 300. After the bridges are removed, the central pieces forming the solder areas 154 5 are only coupled to the component body via the viscoelastic material 155. The fifth embodiment increases flexibility of the additional support structure and thus further improves attenuation of vibration by creating a dampening structure that is coupled to package body only by viscous material.The solder areas 154 may be coupled to any potential on the 10 PCB 700. Preferably, the solder areas are coupled to a DC potential, and more preferably to ground potential. In the fifth embodiment, the solder areas 154 are not electrically coupled to other metal parts of the lead frame inside the package body 300.

It is apparent to a person skilled in the art that as technology advanced, 15 the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims (14)

1. Claims

   1. A semiconductor package comprising

   - a package body;

   - at least one semiconductor die disposed within the package

   5 body; and

   - a lead frame manufactured from a planar sheet of metal, the sheet of metal defining a reference plane, and the lead frame comprising:

   - a die attach paddle onto which the at least one

   10 semiconductor die is attached,

   - a plurality of bond pads, and

   - a plurality of leads coupled to the plurality of bond pads, wherein the leads are configured to provide connections between the at least one semiconductor die and outside of the 15 semiconductor package via bond wires coupling the at least one semiconductor die with the plurality of bond pads;

   characterized in that the lead frame further comprises:

   - at least one additional support structure extending from the lead frame to the bottom surface of the package body, wherein

   20 the at least one support structure is configured to form at least one solder area exposed at the bottom surface of the package body.
2. 2. The semiconductor package according to claim 1, wherein the at 25 least one additional support structure comprises an arm and a handle, wherein the arm is configured to extend from at least one other part of the lead frame, wherein the arm couples the handle to the at least one other part of the lead frame, and wherein the handle is configured to have its bottom surface exposed at the

   20185187 PRH 28 -02- 2018 bottom surface of the package body, and wherein at least part of the bottom surface of the handle is configured to form the solder area.
3. 5 3. The semiconductor package according to any of claims 1 to 2, wherein the at last one additional support structure extends from any of the die attach paddle, at least one bond pad and at least one tie-bar of the lead frame.

   10 4. The semiconductor package according to any of claims 2 to 3, wherein the arm bent towards the bottom surface of the package body is configured to cause the handle to be disposed on a first plane parallel with the reference plane, wherein the first plane resides below the reference plane.

   5. The semiconductor package according to any of claims 2 to 4, wherein a layer of viscoelastic material is disposed between the handle and the package body.

   20
4. 6. The semiconductor package according to any of claims 2 to 5, wherein the solder area is formed by the entire exposed bottom surface of the handle, and wherein the solder area is attached to the arm via the handle.

   25
5. 7. The semiconductor package according to claim 5, wherein the handle comprises a frame and a central piece forming the solder area, and wherein the frame is attached to the arm and the central piece is attached to the frame and to the package body only by the layer of viscoelastic material.

   20185187 PRH 28 -02- 2018
6. 8. The semiconductor package according to any of claims 1 to 7, wherein the essentially planar die attach paddle is disposed at a second plane parallel to the reference.

   5
7. 9. A method to manufacture a semiconductor package with a lead frame, the method comprising:

   - patterning an essentially planar sheet of metal for forming the lead frame, the sheet of metal defining a reference plane, the lead frame comprising:
8. 10 - a die attach paddle coupled to the rest of the lead frame with at least one tie-bar;

   - a plurality of bond pads;

   - a plurality of leads coupled to the bond pads; and

   - at least one additional support structure;

   15 - bending at least part of the at least one additional support structure below the reference plane;

   - attaching at least one semiconductor die to the die attach paddle;

   - bonding the at least one semiconductor die to a plurality of

   20 bond pads via a plurality of bond wires;

   - molding a package body using a mold, wherein the die attach paddle, the at least one semiconductor die, and the plurality of bond pads are disposed entirely inside the package body, and wherein the leads extend outside the package body, and

   25 wherein at least one solder area is formed at the bottom surface of the package body by at least part of the additional support structure exposed at the bottom surface of the package body.

   20185187 PRH 28 -02- 2018

   10. The method according to claim 10, wherein the at least one additional support structure comprises an arm and a handle, wherein the arm is configured to couple the at least part of the handle to the rest of the lead frame, and wherein the method

   5 further comprises:

   - exposing the solder area formed by the at least part of the bottom surface of the handle at the bottom surface of the package body by cleaning the bottom surfaces by any of chemical deflashing, electrolytic deflashing, plasma etching and

   10 grinding.
9. 11. The method according to any of claims 10 to 11, wherein the patterning comprises extending the at last one additional support structure from any of the die attach paddle, at least one

   15 bond pad and at least one tie-bar of the lead frame.
10. 12. The method according to any of claims 10 to 12, wherein the method further comprises:

    - covering the handle with a layer of viscoelastic material prior to

    20 molding the package body.
11. 13. The method according to claim 13, wherein the step of exposing comprises:

    - cleaning the layer of viscoelastic material away from the

    25 bottom surface of the handle for forming the solder area from at least part of the bottom surface of the handle.
12. 14. The method according to any of claims 13 to 14, wherein the handle comprises a frame and a central piece coupled to the

    30 frame with a plurality of thin metal bridges, wherein the layer of viscoelastic material essentially fills the gap between the frame and the central piece, and wherein the step of exposing comprises:

    - grinding the bottom surface of the package body and the

    5 bottom surface of the handle so that the thin metal bridges are removed by the grinding, so that the frame remains attached with the arm and the central piece forming the solder area is attached to the frame and to the package body only by the layer of viscoelastic material.
13. 15. The method according to any of claims 10 to 15, wherein the method further comprises:

    - bending the tie-bars so that the essentially planar die attach paddle is disposed at a second plane parallel to the reference

    15 plane.
14. 16. The method according to any of claims 10 to 16, wherein the lead frame is an inverted lead frame.