WO2024132158A1

WO2024132158A1 - A pin for semiconductor packaging

Info

Publication number: WO2024132158A1
Application number: PCT/EP2022/087532
Authority: WO
Inventors: Kongjing LI; Yangang WANG
Original assignee: Dynex Semiconductor Limited; Zhuzhou Crrc Times Semiconductor Co. Ltd
Priority date: 2022-12-22
Filing date: 2022-12-22
Publication date: 2024-06-27

Abstract

A pin (200) for use in power semiconductor packaging, the pin (200) comprising: a head (202) being shaped to allow a connection to an external connector; a base (204); a barrel (210) comprising a hollow cylindrical shaft, the barrel (210) being located between the head (202) and the base (204); and a pressure means (302) being located in the barrel (210), wherein the hollow cylindrical shaft of the barrel (210) surrounds the pressure means (302); wherein the head (202) and the base (204) are connected to opposite ends of the pressure means (302), such that the head (202) and the base (204) are able to move relative to one another and to the barrel (210).

Description

A Pin for Semiconductor Packaging

FIELD OF THE DISCLOSURE

The disclosure relates to a pin, particularly but not exclusively to a press-fit pin for use in power semiconductor packaging.

BACKGROUND

Semiconductor devices are often enclosed in packaging to protect delicate components. Pins are generally provided to allow connections between semiconductor components within the packaging and other external devices, each pin including a head and a base joined by a rigid body. These pins must be attached to the internal device somehow, typically by soldering the base of the pin to a substrate. The body of the pin generally then protrudes through a hole in the packaging so that the head is outside the packaging, allowing connections to be made between the head and external devices. The pin is not generally soldered or attached anywhere except at the base.

Within this context, press-fit pin heads are commonly known for their ease of use in making additional connections to a power semiconductor device. However, issues can arise wherein a force applied to the head of a press-fit pin - for example, rough handling while attaching a connector - can result in the solder at the base of the pin being broken. Once this happens the pin cannot be used until the semiconductor packaging is opened to permit access to the soldered connection for repairs.

Press-fit technology is widely known in the inverter production industry due to easy fixing to the driver board. The technology has mainly been used for electrical connections between a PCB board and the auxiliary terminals of the power modules. Generally speaking, pin bases are soldered on Direct Bond Copper (DBC) substrates, with pin heads inserted into the board without soldering. This raises several challenges in power module applications, the most critical one being how to fix the pin on the substrate given press/stretch forces arising while connected to the driver board. In Electric Vehicle (EV) applications, frequent vibrations are another important reliability issue needing to be considered, requiring the pin to have a stress releasing design. The current press-fit pin design principle of power modules for EV applications is to solder a rivet (a short hollow cylinder) on the substrate first, and then insert the pin bottom tip into the rivet. This solution doesn’t have stress/strain realising features, leading to high failure risks.

Fig. 1 shows a packaged semiconductor module 100 according to the prior art, including a press-fit pin 102 protruding through a hole 104 in the module lid 106 allowing for external connections to be made to the pin head 108. The base 110 of the pin 102 is bonded to the semiconductor substrate 112, commonly using solder, ultrasound welding, or laser welding. The press-fit pin 102 may commonly be made from a material such as copper, while the substrate 112 may commonly be made from copper-ceramic-copper and the module lid 106 is commonly made from a polymer material.

There have been various attempts to alleviate this issue, for example by designing pins that have a degree of flexibility in a lower portion of the body of the pin. This may allow the body to flex somewhat, so that a force applied to the head may be accommodated by such flexion without damage to the pin base. It is noted that these attempts have often involved a degree of directionality, such that the pin has some ability to flex in a particular direction but not necessarily in other directions.

US10559905B2, US8087943B2, and US7867016B2 could be considered as prior art.

SUMMARY

The inventors have recognised that there is a need for improved robustness of press-fit connectors or pins for semiconductor applications. In particular, it is desirable for the pin to be able to tolerate greater forces applied to the pin head without breaking the solder applied to the pin base, so that the failure rate of such pins is reduced.

Implementations of the present disclosure provide a press-fit pin with enhanced resistance to external forces and a reduced chance of becoming detached during use.

According to one aspect of the present disclosure there is provided a pin for use in power semiconductor packaging, the pin comprising: a head being shaped to allow a connection to an external connector; a base; a barrel comprising a hollow cylindrical shaft, the barrel being located between the head and the base; and a pressure means being located in the barrel, wherein the hollow cylindrical shaft of the barrel surrounds the pressure means; wherein the head and the base are connected to opposite ends of the pressure means, such that the head and the base are able to move relative to one another and to the barrel.

This has the advantage that there is no rigid connection between the head and base of the pin, such that a force applied to the head of the pin is not directly transmitted to the base, but is transmitted only through extension or compression of the pressure means. When the base is soldered to a substrate during use, the soldered connection is consequently highly resistant to breaking during use. It is particularly noted that this robustness applies regardless of the direction of the force applied to the head, as the pressure means merely extends or compresses as necessary to account for the applied force.

The pressure means may be configured such that, when a force is applied urging the head towards the base, the pressure means compresses such that the head and base move nearer together.

The pressure means may be configured such that, when a sufficiently large force is applied urging the head towards the base, the head and the base each make contact with the barrel, thereby preventing further compression of the pressure means.

This feature has the advantage of providing an end stop to the compression of the pressure means. If too large a compressive force is applied, a rigid stop prevents the pressure means from, for example, compressing until the pin is entirely inside the semiconductor packaging and can no longer be accessed.

The pressure means may be configured such that, when a force is applied urging the head away from the base, the pressure means extends such that the head and base move further apart. The head may comprise a first stopper, the first stopper comprising a widened portion of a lower part of the head, wherein the first stopper is wider than the hollow shaft of the barrel such that the barrel does not move past the first stopper.

The barrel may comprise a second stopper, the second stopper comprising a widened portion of the hollow shaft of the barrel.

The second stopper may be towards a lower end of the barrel.

The base may be wider than the hollow shaft of the barrel, such that the base does not pass through the barrel.

This feature has the advantage of providing an end stop to the barrel’s downward motion when the pressure means is subjected to a compressive force. In particular, the barrel is unable to pass around the base and make direct contact with the semiconductor substrate, potentially causing damage.

The barrel may comprise an extrusion feature near to at least one end of the barrel, each extrusion feature comprising a portion of the barrel with a reduced diameter.

One of the extrusion features may be a head extrusion feature near to the end of the barrel nearest the head, the head comprising a head stopper feature, the head stopper feature comprising a portion of the head with a diameter wider than the head extrusion feature, such that in use the head does not fully withdraw from the barrel.

This feature has the advantage of preventing the head from being pulled out of the barrel during use.

One of the extrusion features may be a base extrusion feature near to the end of the barrel nearest the base, the base comprising a base stopper feature, the base stopper feature comprising a portion of the base with a diameter wider than the base extrusion feature, such that in use the base does not fully withdraw from the barrel.

This feature has the advantage of preventing the base from being pulled out of the barrel during use. The barrel may comprise two extrusion features, one near to each end of the barrel, each extrusion feature comprising a portion of the barrel with a reduced diameter.

The lower surface of the base may comprise a recess, such that when liquid solder is applied to the lower surface, the liquid solder climbs into the recess.

This feature has the advantage of allowing a stronger soldered bond between the base of the pin and a semiconductor substrate, reducing the risk of failure during use.

The pin may be a press-fit pin.

The pressure means may be a spring.

The pressure means may be a helical spring, a disk spring, or a leaf spring.

The base may comprise a lower surface suitable for soldering to a substrate of a semiconductor package.

According to a further aspect of the present disclosure there is presented a semiconductor packaging module comprising: a substrate; a module frame enclosing the substrate, the module frame comprising a hole; and the pin of any preceding claim; wherein the base of the pin is soldered to the substrate; wherein the barrel of the pin extends through the hole, such that the head of the pin is outside the module frame.

The second stopper may be wider than the hole, such that the barrel of the pin is unable to pass its entire length through the hole.

This feature has the advantage of providing an end stop to upward motion of the barrel when the pressure means is subject to a large extending force. In particular, the second stopper may ensure that the pressure means is not made to extend so far that the barrel entirely emerges from the semiconductor packaging. This limit of the extension of the pressure means also limits the tension of the pressure means that may pull on the base, thereby avoiding damage to the soldered bond at the base due to excessive pulling by the pressure means. According to a further aspect of the present disclosure there is presented a method of manufacturing a pin for use in power semiconductor packaging, the method comprising: forming a head shaped to allow a connection to an external connector; forming a base; forming a barrel comprising a hollow cylindrical shaft, the barrel located between the head and the base; and forming a pressure means located in the barrel, wherein the hollow cylindrical shaft of the barrel surrounds the pressure means; wherein the head and the base are connected to opposite ends of the pressure means, such that the head and the base are able to move relative to one another and to the barrel.

These and other aspects will be apparent from the implementations described in the following. The scope of the present disclosure is not intended to be limited by this summary nor to implementations that necessarily solve any or all of the disadvantages noted.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure and to show how embodiments may be put into effect, reference is made to the accompanying drawings in which:

Fig. 1 shows a schematic diagram of a packaged power semiconductor device according to the prior art;

Fig. 2 shows a side view of a pin for use in power semiconductor packaging;

Fig. 3 shows a cross-sectional view of the pin of Fig. 2;

Fig. 4 shows a schematic close-up view of the pin of Fig. 2 protruding through a hole in semiconductor packaging;

Fig. 5 shows a side view of another pin for use in power semiconductor packaging;

Fig. 6 shows a side view of the pin of Fig. 5 with the barrel removed; and

Fig. 7 shows an angled view of the pin of Fig. 5.

DETAILED DESCRIPTION

Implementations will now be described by way of example only. Fig. 2 shows a side view of a press-fit pin 200 suitable for use with a packaged semiconductor device. The pin 200 includes a head 202 and a base 204. The head 202 of the pin 200 is shaped to allow press-fit connections, while the base 204 has a lower surface 206 suitable for soldering to a substrate as part of a packaged semiconductor device. A hollow barrel 210 is disposed in between the head 202 and the base 204, but is not attached to either, such that the head 202 and base 204 are each able to move with respect to the barrel 210. Within the barrel 210, the head 202 and the base 204 are joined by a pressure means 302 (such as a spring) that is not visible in Fig. 2 (see description of Fig. 3 below).

The pressure means or spring 302 may offer the benefit of being able to extend and compress in response to an external force exerted on the head 202, allowing the head 202 to move closer to the base 204 or further away, or indeed to move laterally with respect to the base 204. This allows any force applied to the head 202 of the pin 200 to be mitigated by the extension and compression of the spring, rather than being rigidly applied to the base 204 of the pin 200.

It is particularly noted that if a primarily horizontal force (with respect to the barrel) is applied to the head 202, this may be accommodated by the head 202 moving laterally with minimal extension of the spring 302, so that minimal force is transmitted to the base 204. This is described further below with reference to Fig. 3.

The lowest part of the head 202 generally includes a widened or flared region referred to herein as a first stopper 212. The first stopper 212 is generally designed to be wider than the upper opening of the barrel 210, thereby preventing the head 202 from entering the top of the barrel 210 if too large a compressive force is applied. Similarly, the base 204 is generally formed to be wider than the lower opening of the barrel 210. This then imposes a limit on the maximum compression of the spring 302, so that when both the head 202 and the base 204 are pressed against respective openings of the barrel 210, no further compression is possible.

The barrel 210 may likewise include a widened portion 214, referred to herein as a second stopper 214. The second stopper 214 is discussed in more detail with reference to Fig. 4 below. The lower surface 206 of the base 204 of the pin 200 may comprise a recess 208 that generally acts as a solder climbing feature. That is, such a recess may allow solder disposed between the lower surface 206 and a substrate to more firmly bond with the lower surface 206 by presenting an increased surface area for contact with the solder.

Fig. 3 shows a cross-section through the press-fit pin of Fig. 2. The pressure means or spring 302 can be seen contained with the barrel 210 of the pin 200. As described above, the spring 302 is connected to both the head 202 and the base 204 of the pin 200.

In some implementations, the spring 302 may not be a helical spring, but may rather be a crown spring, a leaf spring, or any other elastic object capable of providing spring-like flexibility and storing mechanical energy. It will be appreciated that such an elastic object may be formed of many materials, including metals, polymers, and composite materials.

It is noted that the hollowness of the barrel 210 affords a degree of lateral freedom to the pressure means or spring 302. This is generally advantageous if, for example, the base 204 is imperfectly soldered to a surface such that the pin 200 stands at a slight angle. In this instance, an external connector connected to the head 202 may exert a lateral component of force on the pin 200 rather than purely vertical. The spring 302 can compensate for this lateral component of force by adopting a slight angle inside the barrel 210. This prevents the lateral component force from being rigidly transmitted directly to the base 204, as would happen if the head 202 and base 204 were joined by a rigid body, potentially resulting in snapping of the imperfect soldered bond at the base 204.

Fig. 4 shows a schematic of the press-fit pin of Fig. 2 inserted through a hole 104 in a semiconductor packaging module lid 106, in an arrangement comparable to that used for the prior art pin 102 of Fig. 1. The lower surface 206 of the base 204 of the press-fit pin 200 is generally bonded to a substrate 112 of the module, for example by solder.

The second stopper 214 is generally designed to be wider than the hole 104, so that the second stopper 214 cannot pass through the hole 104. This has the function of limiting the maximum extension of the spring 302. In particular, if a sufficiently large extensive force is applied that the second stopper 214 meets the module lid 106, the spring 302 cannot extend any further. The maximum extension can be chosen such that the largest possible tension in the spring 302 is not sufficient to break or otherwise damage the solder bond between the base 204 and the substrate 112.

It is noted that, in implementations, the semiconductor packaging module may be narrower than is shown in Fig. 4, so that the second stopper 214 is nearer to the module lid 106.

If the lower surface 206 of the base 204 comprises a recess 208 as described above with reference to Fig. 2, solder generally climbs into the recess 208 to strengthen the bond between the substrate 112 and the lower surface 206.

Fig. 5 shows a further pin 500. The pin 500 has many features in common with the pin 200 discussed above, and the same reference numerals are used for these figures as were used above. The pin 500 additionally includes two extrusion features 502 and 504 near the ends of the barrel 210. Each extrusion feature 502, 504 is one or more regions of reduced diameter of the barrel 210. For example, one or more of the extrusion features may take the form of a tighter ring formed into the surface of the barrel 210. However, each extrusion feature 502, 504 may alternatively take a different form provided that at least one region of reduced diameter of the barrel 210 is provided. For example, one or more of the extrusion features 502, 504 may take the form of a series of indentations in the barrel 210 that do not form a continuous ring of the kind shown in Fig. 5. It will be further appreciated that it is not necessary for both extrusion features 502, 504 to be present, and a barrel 210 could be provided with only one of the two.

One of the extrusion features 502 may be near the end of the barrel 210 that is nearest the head 202, and this extrusion feature 502 is otherwise referred to herein as the head extrusion feature 502. The other extrusion feature 504 may be near the end of the barrel 210 that is nearest the base 204, and this extrusion feature 504 is otherwise referred to herein as the base extrusion feature 504.

Fig. 6 shows the pin 500 with the barrel 210 removed so that the interior spring 302 (discussed above with reference to Fig. 3) is visible. It can be seen that the head 202 of the pin 500 generally comprises a head stopper feature 602, which may take the form of at least one portion of the head 202 with increased diameter. For example, as shown in Fig. 6, the lowest part of the head 202 may flare outwards to form the head stopper feature 602. Alternatively, as discussed above with regard to the extrusion features 502, 504, the head stopper feature 602 may take any form that provides an increased diameter, such as for example a series of protrusions that do not form a continuous ring of the kind shown in Fig. 6.

The head stopper feature 602 is generally wider than the head extrusion feature 502. It will be appreciated from Fig. 6 that, when the barrel is in place around the spring 302, the head stopper feature 602 will be prevented from leaving the barrel by the head extrusion feature 502, due to the generally wider diameter of the head stopper feature 602. As a result, the head extrusion feature 502 prevents the head 202 from being pulled out of the barrel 210 during use, for example if the head is pulled during the detaching of a connector. This further prevents excessive stretching of the spring 302 that may result if the head 202 is pulled entirely out of the barrel 210.

Fig. 6 further shows that the base 204 of the pin 500 generally comprises a base stopper feature 604, which may take the form of at least one portion of the base 204 with increased diameter. For example, as shown in Fig. 6, the uppermost part of the base 204 may flare outwards to form the base stopper feature 604. Alternatively, as discussed above with regard to the head stopper feature 602, the base stopper feature 604 may take any form that provides an increased diameter, such as for example a series of protrusions that do not form a continuous ring of the kind shown in Fig. 6.

In analogy with the head stopper feature 602, the base stopper feature 604 is generally wider than the base extrusion feature 504 such that, in use, the base 204 cannot be entirely withdrawn from the barrel 210 by excessive force.

Fig. 7 shows an angled view of the pin 500 to allow a better appreciation of the three- dimensional nature of the pin 500.

Thus, it can be seen that implementations described herein provide a press-fit pin that is more robust to external forces and less likely to become detached during use. The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘upper’, ‘lower’, ‘above’, ‘overlap’, ‘under’, ‘lateral’, etc. are made with reference to conceptual illustrations of an apparatus, such as those showing standard cross-sectional perspectives and those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to a device when in an orientation as shown in the accompanying drawings.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A pin for use in power semiconductor packaging, the pin comprising: a head being shaped to allow a connection to an external connector; a base; a barrel comprising a hollow cylindrical shaft, the barrel being located between the head and the base; and a pressure means being located in the barrel, wherein the hollow cylindrical shaft of the barrel surrounds the pressure means; wherein the head and the base are connected to opposite ends of the pressure means, such that the head and the base are able to move relative to one another and to the barrel.

2. The pin of claim 1 , wherein the pressure means is configured such that, when a force is applied urging the head towards the base, the spring compresses such that the head and base move nearer to one another.

3. The pin of claim 2, wherein the pressure means is configured such that, when a sufficiently large force is applied urging the head towards the base, the head and the base each make contact with the barrel, thereby preventing further compression of the spring.

4. The pin of any preceding claim, wherein the pressure means is configured such that, when a force is applied urging the head away from the base, the spring extends such that the head and base move away from one another.

5. The pin of any preceding claim, wherein the head comprises a first stopper, the first stopper comprising a widened portion of a lower part of the head, wherein the first stopper is wider than the hollow shaft of the barrel such that the barrel does not move past the first stopper.

6. The pin of any preceding claim, wherein the barrel comprises a second stopper, the second stopper comprising a widened portion of the hollow shaft of the barrel.

7. The pin of claim 6, wherein the second stopper is towards a lower end of the barrel.

8. The pin of any preceding claim, wherein the base is wider than the hollow shaft of the barrel, such that the base does not pass through the barrel.

9. The pin of any preceding claim, wherein the barrel further comprises an extrusion feature near to at least one end of the barrel, each extrusion feature comprising at least one portion of the barrel with a reduced diameter.

10. The pin of claim 9, wherein one of the extrusion features is a head extrusion feature near to the end of the barrel nearest the head, the head comprising a head stopper feature, the head stopper feature comprising at least one portion of the head with a diameter wider than the head extrusion feature, such that in use the head does not fully withdraw from the barrel.

11. The pin of claim 9 or 10, wherein one of the extrusion features is a base extrusion feature near to the end of the barrel nearest the base, the base comprising a base stopper feature, the base stopper feature comprising at least one portion of the base with a diameter wider than the base extrusion feature, such that in use the base does not fully withdraw from the barrel.

12. The pin of any of claims 9-11 , wherein the barrel comprises two extrusion features, one near to each end of the barrel, each extrusion feature comprising at least one portion of the barrel with a reduced diameter.

13. The pin of any preceding claim, wherein the lower surface of the base comprises a recess, such that when liquid solder is applied to the lower surface, the liquid solder climbs into the recess.

14. The pin of any preceding claim, wherein the pin is a press-fit pin.

15. The pin of any preceding claim, wherein the pressure means is a spring.

16. The pin of any preceding claim, wherein the pressure means is a helical spring, a disk spring, or a leaf spring.

17. The pin of any preceding claim, wherein the base comprises a lower surface suitable for soldering to a substrate of a semiconductor package.

18. A semiconductor packaging module comprising: a substrate; a module frame enclosing the substrate, the module frame comprising a hole; and the pin of any preceding claim; wherein the base of the pin is soldered to the substrate; wherein the barrel of the pin extends through the hole, such that the head of the pin is outside the module frame.

19. The semiconductor packaging module of claim 18 when dependent on claim 6 or 7, wherein the second stopper is wider than the hole, such that the barrel of the pin is unable to pass its entire length through the hole.

20. A method of manufacturing a pin for use in power semiconductor packaging, the method comprising: forming a head shaped to allow a connection to an external connector; forming a base; forming a barrel comprising a hollow cylindrical shaft, the barrel located between the head and the base; and forming a pressure means located in the barrel, wherein the hollow cylindrical shaft of the barrel surrounds the pressure means; wherein the head and the base are connected to opposite ends of the pressure means, such that the head and the base are able to move relative to one another and to the barrel.