RU2740788C1 - Method of separating multiplex substrate sealed with epoxy compound into separate microcircuits - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to methods for separation of multiplex substrates (MS) into separate microcircuits and can be used in manufacturing assemblies of microelectronic equipment. Method of separating MS with an epoxy compound containing a plurality of chips sealed with an epoxide compound involves fixation of the MS in a vacuum holder and its separation into separate microcircuits with a saw with a diamond disk working element. Prior to MS separation it is laminated on the side of compound layer with film material with bearing and glue layers. Bearing layer is selected with thickness of not less than 120 mcm, and adhesive layer - with thickness in range from 10 to 40 mcm and peel strength of not less than 20,000 mN/25 mm. MS separation is performed so that film material retains its integrity. Cutting speed is set in range from 44 to 82 m/s, and speed of feed in range from 20 to 40 mm/s. At that, diamond disk working element is abrasively treated.

EFFECT: technical result is reduction of labour intensity of MS separation process due to exclusion of necessity to manufacture accessories for fixation of MS during production of small batch of microelectronic products or prototypes.

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Description

Technology area

The invention relates to electronic engineering and can be used in the manufacture of assemblies of microelectronic equipment, and more specifically, the technical solution relates to methods for dividing multiplied substrates into separate microcircuits containing a plurality of crystals.

Prior art

The traditional packaging process for microelectronic products includes: dividing a semiconductor carrier wafer into individual crystals; mounting the chips on the multiplied substrate and providing electrical connection of the chips to the substrate; sealing the plate with a layer of compound; dividing the substrate into separate microcircuits [1].

Typically, the multiplied substrate has a rectangular shape and is intended for mounting on it a plurality of microcircuits, usually of the same type, for example, such a substrate device is disclosed in US Pat. US 6365438 [2]. The separation of such a substrate can be carried out using a saw with a disk tool mounted on a spindle, which cuts it between microcircuits, for example, a similar technical solution is disclosed in US Pat. US 6413150 [3]. To separate the multiplied substrate, it is fixed on the working surface. After the cutting process, the chips must go through a series of processing steps such as cleaning and drying. To automate this process, it is necessary to ensure the fixation of the orientation of the microcircuits, as well as the possibility of group manipulation (processing and movement of the microcircuits).

Several basic approaches to solving the problem of fixing a multiplied substrate in the process of dividing it into individual microcircuits are known from the prior art. Firstly, methods based on the use of a disposable tape having two adhesive layers located on the front and back sides, with which the multiplied substrate is fixed on the working surface. Secondly, methods involving the use of a frame equipped with a disposable adhesive tape, on which the multiplied substrate is fixed, while the adhesive tape itself is held on the working surface by a vacuum holder (vacuum chuck). Thirdly, methods using specialized devices (conductors) of various designs, reusable. Such methods usually involve placing a multiplied substrate in a conductor, followed by fixing the conductor in a vacuum holder.

For example, the first approach relates to a method of separating a multiplied substrate containing a plurality of crystals into individual microcircuits, including: fixing the multiplied substrate to a working surface by means of an adhesive tape provided with two adhesive layers located on the front and back sides; cutting the substrate in the longitudinal and transverse directions using a saw between different groups of microcircuits placed on the multiplied substrate; separation of the resulting microcircuits from adhesive tape [4].

The disadvantage of this method is the difficulty of ensuring the cleanliness of the working surface, on which the multiplied substrate is fixed due to the remaining particles of the adhesive after the separation of the microcircuits. The presence of adhesive residues affects the overall value of the adhesion force (as a rule, the presence of “old” adhesive particles on the working surface impairs adhesion). Insufficient adhesion strength can lead to displacement of the multiplied substrate during the cutting process. Even a slight misalignment can damage many ICs. Therefore, additional operations are required to keep the working surface clean.

In addition, the method does not allow separating the multiplied plate on equipment where methods using vacuum holders (second and third approaches) can be carried out. In practice, this may be inconvenient as it does not provide flexibility in the production process.

An example of a second approach is a method for dividing a multi-crystal multiplied substrate into individual microcircuits, comprising: providing a disposable carrier tape with an adhesive layer on one of its sides characterized by reduced adhesion under the influence of ultraviolet radiation; fixing the carrier tape in an annular support (frame); fixing the multiplied substrate to a carrier tape mounted in an annular support; fixing the annular support and the carrier tape on the vacuum holder; cutting the substrate longitudinally and transversely using a saw between different groups of microcircuits placed on the multiplied substrate so that the carrier tape retains its integrity; irradiation of the carrier tape with ultraviolet radiation; separation of microcircuits from the carrier tape [3].

The disadvantage of this method is the significant consumption of the carrier tape. This is due to the fact that the area of the carrier tape must be greater than the area of the multiplied substrate, since additional areas are required to be allocated for fixing the carrier tape in the annular support. The carrier belts are made from polymeric materials that have a negative impact on the environment. Therefore, the increased consumption of the carrier tape is a negative factor in the process of manufacturing microelectronic products for the environment. In addition, the need to fix the carrier tape in an annular support increases the labor intensity and reduces the productivity of the process of separating the multiplied substrate.

Also, the disadvantage of the described method is expressed in the fact that the use of an annular support increases the occupied area of the multiplied substrate when it is cut. This leads to the need to increase the working space in which the separation operation is carried out, which reduces the list of equipment that can be used.

An example of a third approach is a method of dividing a multiplied substrate containing a plurality of crystals into individual microcircuits, including: securing a conductor on a vacuum holder; fixing the multiplied substrate in the conductor; cutting the multiplied substrate using a saw with a disk working body between different groups of microcircuits [5].

This method provides a high productivity and degree of automation of the process of separating the multiplied substrate in comparison with the above-described analogs. However, there are several disadvantages. The conductor is made strictly for a specific type of microcircuits and their configuration of placement on a multiplied substrate. Therefore, new configurations of microcircuits require the manufacture of new conductors.

The jig is a relatively complex device that requires a high degree of manufacturing accuracy (dimensional accuracy). The manufacture of new conductors leads to an increase in labor costs of the entire process of packaging microelectronic products and, in general, reduces the flexibility of the production process. This problem is especially relevant in the context of small-scale and pilot production, where packaged microelectronic products are often changed, and their batches are insignificant.

Multi-chip microelectronic assemblies are widely adopted, where various chip mounting technologies, in particular Wire Bond and Flip-Chip, are applied in the same package. Such microelectronic assemblies can be relatively quickly designed to meet customer requirements. This has led to an increase in the need for the manufacture of small batches of microelectronic products. However, as a rule, when using the method described above, changing the circuit design of a microelectronic assembly requires the manufacture of a new conductor. In addition, with an increase in the density of microcircuits and a decrease in their geometric dimensions (one of the main trends in microelectronics), the laboriousness of the manufacture of a conductor increases.

The closest technical solution, selected as a prototype, is a method of dividing a multiplied substrate sealed with a compound, containing a plurality of crystals, into separate microcircuits, including: feeding and placing a multiplied substrate containing a plurality of crystals sealed with a compound layer on a saw jig; fixing the multiplied substrate in the saw jig on the vacuum table; feeding a vacuum table with a multiplied substrate to the cutting place; sawing the multiplied substrate into separate microcircuits; moving the vacuum holder with the sawn multiplied substrate to the unloading area; capture by a vacuum head of microcircuits and move them to the washing and drying area; washing and drying of microcircuits; moving microcircuits to the unloading area and concentration of microcircuits in the container [6].

This method allows for high productivity and the degree of automation of the process of separating the multiplied substrate. The disadvantage of this method is the need to manufacture new tooling when changing the configuration of the multiplied substrate (the shape of the multiplied substrate, the location and size of the microcircuits on the multiplied substrate), which leads to an increase in labor intensity and a decrease in the flexibility of the process of manufacturing microelectronic products, especially in conditions of small-scale and pilot production, where the configuration is multiplied substrates can be changed frequently.

Thus, a technical problem is the need to develop a process for dividing the multiplied substrate into individual microcircuits without the need to manufacture tooling for fixing it on equipment that requires such a tooling.

Disclosure of invention

The technical result, which the claimed technical solution is aimed at, is to reduce the labor intensity of the process of dividing the multiplied substrate into individual microcircuits due to the fact that there is no need to manufacture equipment for fixing the multiplied substrate in the production of a small batch of microelectronic products or prototypes.

An additional technical result is an increase in the flexibility of the process of manufacturing microelectronic products in view of the fact that on the equipment, assuming the use of tooling, the separation of the multiplied substrate without such tooling can be provided.

The technical result is achieved by the fact that the method of dividing a multiplied substrate containing a plurality of crystals into separate microcircuits sealed with an epoxy compound includes fixing the multiplied substrate in a vacuum holder and separating it into separate microcircuits with a saw with a diamond disk working body, while before dividing the multiplied substrate into individual microcircuits carry out its lamination from the side of the compound layer with a film material with a carrier and adhesive layers, and the carrier layer of the film material is selected with a thickness of at least 120 μm, and the adhesive layer with a thickness in the range from 10 to 40 μm and a peel strength of at least 20,000 mN / 25 mm, and the division of the multiplied substrate into individual microcircuits is performed in such a way that the film material retains its integrity, and the cutting speed is set in the range from 44 to 82 m / s, and the feed rate in the range from 20 to 40 mm / s, while perio Generally, the diamond disk tool is abraded.

Implementation of the invention

The claimed technical solution is part of the packaging process, at the first stages of which a multiplied substrate is manufactured, sealed with an epoxy compound and containing a lot of crystals. Before starting the separation process of the multiplied substrate, the absence of defects is monitored on it. For this, inspection microscopes, for example, can be used.

Then, the multiplied substrate is laminated from the side of the compound layer with a film material with a carrier and adhesive layers. For this, laminating machines can be used, which are usually used to laminate semiconductor wafers before thinning them. Lamination can be carried out with a film (including UV film) with an adhesive layer. The lamination process includes: securing the multiplied substrate to the receiving table, for example, by means of vacuum holders; gluing the film material to the substrate from the side of the compound layer; trimming of parts of the film material protruding from the edges of the plate (if necessary); and quality control of lamination. The quality control of the lamination checks for air bubbles and contamination under the film material, which can lead to displacement of the multiplied substrate during the cutting process. In case of defects, the film material is removed. Then the lamination operation is repeated.

The carrier layer of the film material is selected with a thickness of at least 120 μm, and the adhesive layer is selected with a thickness in the range from 10 to 40 μm and a peel strength of at least 20,000 mN / 25 mm. The thickness of the carrier layer is due to the need to provide the required rigidity of the film material, which, when separated, is a spacer between the multiplied substrate and the working surface. If the elastic modulus of the carrier layer is insufficient, several problems arise. First, during cutting, an increase in the size of chips is observed on the back side of the multiplied substrate (from the side of the epoxy compound), which is critical at a high density of crystals.

Secondly, during cutting, the insufficient rigidity of the carrier layer does not allow for the alignment of the stress distribution diagram over the entire bonding area of the film material. This reduces the strength of the adhesive bond and under reasonable cutting conditions (cutting speed from 44 to 82 m / s, feed rate from 20 to 40 mm / s) increases the likelihood of displacement of the multiplied substrate during its division into individual microcircuits.

Third, when fixing the multiplied substrate, insufficient rigidity of the carrier layer leads to the formation of irregularities in the places where the channels of the vacuum holder adjoin the film material, which reduces the fixing strength and increases the likelihood of displacement of the multiplied substrate during cutting.

The film material is made of polyolefins or polyvinyl chloride. With a carrier layer thickness of more than 120 microns and using the selected cutting conditions (cutting speed from 44 to 82 m / s, feed rate from 20 to 40 mm / s), the required rigidity of the film material is provided. With a thickness of less than 120 microns, the quality of the cut is not sifted (significant chips are observed), and the case of displacement of the multiplied substrate during the cutting process becomes more frequent. It is expedient to use a film material with a carrier layer of about 140 μm thickness. The use of a film material with a layer thickness of more than 140 microns is not advisable for economic reasons. With a thickness of more than 140 microns, the material consumption of the film material increases, and, accordingly, its cost. However, the separation quality of the multiplied substrate is ensured.

Typically, the thinner the adhesive layer, the greater the bond strength. There are several reasons for this. With an increase in the thickness of the adhesive layer, the probability of formation of defects in the layer increases, which reduces the strength of the adhesive bond. In addition, the thickness of the adhesive layer determines the magnitude of the internal stresses. The greater the thickness, the greater the internal stresses in the adhesive layer.

The multiplied substrate during the installation of crystals on it, the electrical connection of the crystals to the substrate, sealing with epoxy compound due to the effect of elevated temperatures on materials with different coefficients of thermal expansion, as well as due to the occurrence of temperature gradients, is subject to warping. The amount of warpage can be reduced, but it is not possible to completely eliminate this phenomenon in practice. In addition, it should be noted that when sealing the multiplied substrate, the resulting surface, which will then be lamination, is also not ideal and has nervousness. Therefore, a thin adhesive layer does not provide the necessary adhesion over the entire area of contact between the film material and the surface of the multiplied substrate, which can lead to its displacement during cutting. To compensate for these phenomena, the thickness of the adhesive layer must be at least 10 microns.

The upper limit of the interval for choosing the thickness of the adhesive layer is determined by an increase in the probability of formation of defects in the layer and internal stresses. Modern technologies for the manufacture of film materials with an adhesive layer allows minimizing the indicated negative phenomena. However, the upper limit of the range of the thickness of the adhesive layer is limited by another phenomenon. In the process of cutting with an adhesive layer thickness of about 40 microns and more, an increase in chips is observed on the reverse side of the multiplied substrate. This is due to the fact that the modulus of elasticity in the abutment zone of the adhesive layer and the surface of the multiplied substrate is insufficient (the rigidity of the adhesive layer is less than the rigidity of the carrier layer). The particles on the surface of the multiplied substrate during the introduction of the disk working body do not have the necessary support (due to the thickness of the adhesive layer) and are pulled out. Thus, for the selected cutting conditions, the thickness of the adhesive layer should be selected from the range from 10 to 40 microns. It is advisable to use an adhesive layer thickness of about 30 µm.

The peeling strength of the adhesive layer at the selected cutting conditions (cutting speed from 44 to 82 m / s, feed rate from 20 to 40 mm / s) must be at least 20,000 mN / 25 mm. At a peel strength of less than 20,000 mN / 25 mm, there is a sharp increase in the likelihood of displacement and / or peeling of the multiplied substrate. It is advisable to use a film material with a peel strength of 25,000 mN / 25 mm. This will reliably fix the multiplied substrate and prevent it from shifting or peeling.

Peel strength is determined using a 180 ° peel strength test [7]. In the test, when the two components peel apart, a constant angle of 180 ° is maintained. The average load required to separate the two components is recorded and expressed as mN / 25 mm, with a sample 25 mm wide and 250 mm long. The sample is clamped in a gripper. The two components are separated from each other by a traverse movement at a speed of 300 mm / min.

After laminating the multiplied substrate, it is fed into the sawing area and aligned according to the predetermined marks. After alignment, the substrate is fixed on the working surface with a vacuum holder. Fixation is carried out from the side of the film material. The vacuum holder holds the film material, which in turn fixes the multiplied substrate due to the adhesive layer. The configuration of the vacuum holder in this case does not depend on the shape of the multiplied substrate, location and size of microcircuits on the multiplied substrate. Immediately before fixing the substrate (before turning on the vacuum holder), its position and orientation are monitored. This operation can be carried out using specialized cameras, which are equipped with equipment for separating substrates.

Then, the multiplied substrate is divided into individual microcircuits so that the film material retains its integrity. The cutting of the substrate is carried out with a saw with a diamond disk working body, and the cutting speed is set in the range from 44 to 82 m / s, and the feed rate in the range from 20 to 40 mm / s.

The diameter of diamond disc working bodies used to separate the multiplied substrate is 50-60 cm. The thickness of the working body is less than 0.3 mm and is determined by the width of the required cut when separating the multiplied substrate. Usually saws with a thickness in the range of 0.2-0.26 mm are used to separate the substrate. When separating the substrate, the depth of cut usually does not exceed 1 mm, usually 0.6-0.7 mm, and is determined by the thickness of the multiplied substrate.

The characteristics (grain size and concentration) of the coating of the diamond disk working body under the same cutting conditions can significantly affect the quality of the cut / surface finish, the size and number of chips, and the nature of damage to the material microstructure. Cutting with blades with coarse abrasive particles (diamond grains) is generally more productive than cutting with blades with fine particles. However, this increases the number of microdamages in the material. When cutting multiplied substrates, diamond discs with finer abrasive particles are used, namely, with a maximum diamond grain size of no more than 40 microns and a concentration of about 3.3 carats / cm ³ .

Modern equipment makes it possible to provide a cutting speed with a diamond disk working body up to 160 m / s and spin the disk up to 60,000 rpm. Increasing the cutting speed improves the quality of the cut. It should also be noted that the used disk working bodies have a thickness of no more than 0.3 mm. With an increase in the cutting speed due to an increase in centrifugal forces, the rigidity of the working body increases, which is important when determining the feed rate, which in turn determines the magnitude of the cutting force.

However, increasing the cutting speed only to a certain value will increase the quality of the cut. Up to approximately 73 m / s (about 23000-27000 rpm for the used disk working bodies), an increase in the cutting speed improves the quality of cutting the multiplied substrate. This is due to an increase in the stability of the engine spindle, on which the disk working body is installed, and a decrease in vibration.

A further increase in the cutting speed over 73 m / s leads to a decrease in the quality of the cut. This is due to an increase in the amplitude of vibrations of the disc organ, especially in the horizontal plane. An increase in the amplitude leads to an increase in the number of chips on the surface. At about a cutting speed above 82 m / s (about 27000-31000 rpm), there are cases of displacement of the multiplied substrate, fixed on the working surface, during its separation due to partial destruction of the adhesive layer.

When the cutting speed drops below 73 m / s, the quality of the cut decreases, i.e. the number of chips and cracks on the surface of the multiplied substrate increases, and delamination of the substrate material is also observed. In addition, the stiffness of the disk working body decreases, which causes its deformation and ultimately leads to an increase in the negative impact on the quality of the substrate separation (increased vibration). At a feed rate from 20 to 40 mm / s, an acceptable quality of the cutting operation of the multiplied substrate is provided at a minimum cutting speed of about 44 m / s (about 14000-17000 rpm).

When using jigs, the feed rate (usually the table with the substrate is fed, and the saws are stationary) when dividing the multiplied substrate is in the range of 80-150 mm / s. However, at such a feed rate, it is difficult to select the required cutting speed and ensure reliable fixation of the substrate solely due to the adhesive layer of the film material and ensure the quality of the cut. Reliable fixation of the multiplied substrate at the selected cutting speed and characteristics of the film material is provided at a feed rate of 30 ± 10 mm / s, i.e. from 20 to 40 mm / sec. An increase in the feed rate leads to an increase in the required cutting force and, in the general case, an increase in the level of vibration and an increase in the likelihood of displacement of the multiplied substrate. It makes no sense to choose a feed rate of less than 20 mm / s, as it leads to a decrease in the productivity of the operation of separating the multiplied substrate. It is advisable to choose values closer to the upper limit of the specified range of feed rate, but not to exceed it. This will ensure an acceptable cut and will prevent the substrate from shifting.

In the process of cutting, the heated (due to friction during sawing) disk working body interacts with the adhesive layer of the film material when cutting the multiplied substrate. The adhesive enters the pores (the space between the diamond grains) and gradually fills them. In the pores, the adhesive also traps particles of the multiplied substrate and makes it difficult to peel off the spent diamond grains. The characteristics of the disk working body change and the "efficiency" of the selected cutting modes decreases: the number of chips, cracks and delamination increases, and the likelihood of displacement of the multiplied substrate increases.

To eliminate the influence of contamination, the disk working body is periodically abrasive processed. For these purposes, either the equipment for cutting substrates should be equipped with a station for straightening disk working bodies (a surface with a fixed plate made of abrasive material), or periodically feeding a plate of abrasive material fixed on the working surface into the cutting zone (an abrasive plate fixed instead of a multiplied substrate ). At the same time, the disc working body, in contact with the abrasive material, is cleaned and restores its original characteristics.

After the cutting process, particles of the substrate, compound, disk working body remain on the separated microcircuits. The microcircuits on the film material (cut) are transferred to the cleaning site, where they are washed with deionized water, and then the remaining moisture is removed with compressed air. Additionally, mechanical cleaning with brushes can be carried out before flushing.

Further, the microcircuits on the film material are moved to the next processing location for further operations related to the manufacture of microelectronic products. The film material holds the microcircuits on itself and allows you to maintain their orientation, as well as to provide group manipulation over them.

Thus, the proposed method makes it possible to reduce the complexity of the process of separating electronic packages, since it is not required to manufacture tooling for new microelectronic products. In addition, the production process is flexible. If it is necessary to produce large batches of microelectronic products, a conductor is made and a known method for separating a multiplied substrate is used. When a need arises for the production of a small batch of microelectronic products, the same equipment is used using the proposed technical solution.

Bibliography

1. Morkner G. Miniature GaAs-monolithic microcircuits for applications in the range of DC-45 GHz, made according to KP technology // Wireless technologies - 2010 - №4 - P. 24-28.

2. Patent for invention US 6165232 "Process for manufacturing semiconductor package and circuit board assembly", published 02.04.2002.

3. Patent for invention US 6413150 "Dual dicing saw blade assembly and process for separating devices arrayed a substrate", published 02.07.2002.

4. Patent for invention US 6087202 "Process for manufacturing semiconductor packages comprising an integrated circuit", published on July 11, 2000.

5. Patent for invention US 7438286 "Workpiece holding jig", published 09.21.2008

6. Patent for invention US 8011058 "Singulation handler system for electronic packages", filed on 26.10.2007.

7. Peel adhesion test: https://www.impact-solutions.co.uk/peel-adhesion-test/

Claims (1)

A method of dividing a multiplied substrate containing a plurality of crystals into separate microcircuits sealed with an epoxy compound, comprising fixing the multiplied substrate in a vacuum holder and separating it into separate microcircuits with a saw with a diamond disk working body, characterized in that before dividing the multiplied substrate into separate microcircuits, it is carried out lamination from the side of the compound layer with a film material with a carrier and adhesive layers, and the carrier layer of the film material is selected with a thickness of at least 120 microns, and the adhesive layer with a thickness in the range from 10 to 40 microns and a peel strength of at least 20,000 mN / 25 mm, and the separation the multiplied substrate on individual microcircuits is performed in such a way that the film material retains its integrity, and the cutting speed is set in the range from 44 to 82 m / s, and the feed rate is in the range from 20 to 40 mm / s, while periodically diamond disk work whose organ is abrasively treated.