Semiconductor module with serial bus connection to multiple dies

Abstract

A semiconductor module is provided which includes a beat heat spreader, at least two semiconductors thermally coupled to the heat spreader, and a plurality of electrically conductive leads electrically connected to the semiconductors. At least one of the electrically conductive leads is common to both of the semiconductors The semiconductor module also includes a termination resistor electrically coupled to at least one of the semiconductors. A method of making a semiconductor module is also taught, whereby a plurality of electrically conductive leads are provided. At least two semiconductors are electrically coupled to the plurality of electrically conductive leads, where at least one of the electrically conductive leads is common to both of the semiconductors. The semiconductors are then thermally coupled to a heat spreader. Subsequently, a termination resistor is electrically coupled to at least one of the semiconductors.

Description

This application 1115 (FIG. 10) to protect the semiconductor from electromagnetic forces. In addition, adhesive may be placed between the tape and the base of the heat spreader to cushion the contact points and ensure contact between the contact points and the PCB.

The semiconductor module of the invention eliminates the need for a separate heat spreader. The invention reduces overall cost and weight through shared common contact points or nodes. The common contact points also allow for a constant footprint to be maintained independent of the size or number of semiconductors used. Furthermore, the module is reliable as the semiconductors are not exposed to as high thermal stresses. The module also substantially improves heat dissipation by exposing greater surface areas to the surrounding air.

Multi-Chip Modules

As explained above in the background section of this specification, many existing semiconductor modules position their embedded semiconductors relatively far from the circuit board to which they are attached. Each semiconductor in such semiconductor modules connects to a transmission channel via its own electrical lead. A signal passing along the transmission channel from lead to lead is degraded by a load placed on the signal by each successive lead. The longer the stub, the more the signal is degraded. Each successive lead further degrades the signal, until such time as the signal has been degraded so as to be useless. Most semiconductor modules also include a termination resistor at the end of each transmission channel on the printed circuit board. The present invention addresses the problem associated with signal degradation in semiconductor modules having relatively long electrical leads.

Impedance matching of an electrical load to the impedance of a signal source and the characteristic impedance of a transmission channel is often necessary to reduce reflections by the load, back into the transmission channel. As the length of a non-terminated transmission line increases, reflections become more problematic. When high frequency signals are transmitted or passed through even very short transmission lines, such as printed circuit board (PCB) traces, a termination resistor may be inserted at the load to avoid reflections and degradations in performance.

In the multi-chip modules of the present invention, termination resistors are preferably internal to the MCM's. The use of external termination resistors presents a number of drawbacks. The placement of a termination resistor outside an MCM results in an additional stub or short transmission line between the termination resistor and the integrated circuit device. External termination resistors also require significant circuit board space, and increase circuit board layout complexity and cost.

FIG. 12 shows a side view of a semiconductor module 1200 according to yet another embodiment of the invention. A number of semiconductors 1204 are electrically coupled to a plurality of traces or electrically conductive leads 1202 (only one is shown) by any conventional method such as wire bonding or thermocompression bonding. The electrically conductive leads 1202 are preferably incorporated into a flexible circuit or tape 1210, which preferably consists of copper traces within a thin dielectric substrate (such as polyimide, epoxy, etc.).

The semiconductors 1204 on the flexible circuit 1210, are preferably bonded directly to a heat spreader 1218. Alternatively, as shown and described in relation to FIG. 2, the flexible circuit 1210 may be bonded directly to the heat spreader 1218. The bond may be made by any means but is preferably made by gluing the semiconductors 1204 or flexible circuit 1210, with an epoxy or the like, to the side of the heat spreader 1218. The glue is chosen to closely match the thermal expansion properties of the semiconductor 1204, heat spreader 1218, and flexible circuit 1210. The glue should also have good thermal conduction properties. This embodiment, where the semiconductors 1204 are bonded directly to the heat spreader 1218 is favored due to the direct conduction of heat from the semiconductors 1204 to the heat spreader.

The heat spreader 1218 is preferably made from a material with good heat dissipation properties, such as a metal. In a preferred embodiment, the semiconductors 1204 are positioned on opposing sides of the heat spreader 1218. The electrical leads 1202 connect the semiconductors 1204 to electrical contact points 1216 at the base of the semiconductor module 1200. In use, electrical contact points 1216 may for example comprise solder balls or bond pads. The electrical contact points 1216 electrically couple the electrical leads 1202 to a transmission channel 1214 on a printed circuit board 1212. Electrical signals are transmitted along the transmission channel 1214 to electrical contact points 1216. The electrical signals are then passed from the electrical contact points 1216 through the electrical leads 1202 to each of the semiconductors 1204.

In this embodiment, the semiconductors 1204, on opposing sides of the heat spreader 1218, are connected to one another in series by the electrical lead 1202. It should be noted that multiple (i.e., more than two) semiconductors 1204 may be connected together in series. The final semiconductor in the series, remote from the transmission channel, electrically couples to a termination resistor 1208. The termination resistor 1208 is preferably thermally coupled to the heat spreader 1218 so that any heat built up in termination resistor 1208 can dissipate through the heat spreader.

The termination resistor 1208 connected in series to the semiconductors 1204 substantially reduces any degradation of the signal caused by a load placed on the signal from the electrical leads 1210, as the signal is not being split as is the case with stubs in existing semiconductor modules. A signal is transmitted from a signal source along the transmission channel 1214, along an electrical lead 1202, to each semiconductor 1204 connected in series, and is terminated at the termination resistor 1208. Furthermore, by incorporating the termination resistor 1208 into the semiconductor module 1200, the need for a termination resistor on the printed circuit board 1214 is eliminated.

This embodiment of the invention is particularly useful now that the memory capacity of individual semiconductors has increased to a point where only a few semiconductors are needed for many applications.

FIG. 13 is a front view of the semiconductor module 1300 according to a further embodiment of the invention. This semiconductor module 1300 is identical to the semiconductor module 100 shown in FIG. 1, except for a termination resistor 1302 disposed on the heat spreader. FIG. 14 is a side view of the same semiconductor module 1300 shown in FIG. 13. In this embodiment, the semiconductors 1304 are not connected in series, but rather each semiconductor connects to its own transmission channel. Likewise, each termination resistor 1302 connects to a single semiconductor. In use, a signal is transmitted along each transmission channel, to its respective semiconductor, after which it is terminated at a termination resistor 1402 to eliminate reflections.

The resistance value of the termination resistor 1208 (FIG. 2) or 1302 (FIGS. 13 and 14) is selected such that its impedance substantially matches the impedance of the transmission channel and signal source to which it is connected. Furthermore, any form of termination may be used, such as parallel termination, Thevenin termination, series termination, AC termination, Schotty Schottky-diode termination or the like.

FIG. 15 is a flow chart of a method 1500 of making a semiconductor module according to another embodiment of the invention. According to the method 1500 a plurality of electrically conductive leads are provided (step 1502). At least two semiconductors are electrically coupled (step 1504) to the plurality of electrically conductive leads, where at least one of the electrically conductive leads is common to both of the semiconductors. The semiconductors are then thermally coupled (step 1506) to a heat spreader. Subsequently, a termination resistor is electrically coupled (step 1508) to at least one of the semiconductors.

The semiconductors may be electrically coupled in series, where the semiconductors are capable of being electrically coupled to a transmission channel. Moreover, an additional termination resistor may be electrically coupled to the semiconductor not already connected to the termination resistor, where each of the semiconductors is capable of being electrically coupled to a separate transmission channel.

While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the present invention as defined in the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other specific forms, structures, arrangements, proportions, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and not limited to the foregoing description.

Claims

1. A semiconductor module, comprising:

a heat spreader;

at least two semiconductors thermally coupled to said heat spreader;

a plurality of electrically conductive leads electrically connected to said semiconductors, where at least one of said electrically conductive leads is common to both of said semiconductors; and

a termination resistor electrically coupled to at least one of said semiconductors.

2. A semiconductor module according to claim 1, wherein said semiconductors are electrically coupled to one another in series, and where said semiconductors are capable of being electrically coupled to a transmission channel.

3. A semiconductor module according to claim 2, wherein a final semiconductor in said series, remote from said transmission channel, is electrically coupled to said termination resistor.

4. A semiconductor module according to claim 1, wherein one semiconductor of the semiconductors is not connected to said termination resistor, and an additional termination resistor is electrically coupled to the one semiconductor not connected to said termination resistor.

5. A semiconductor module according to claim 1, wherein a resistance value of the termination resistor is selected such that an impedance of said termination resistor substantially matches an impedance of a transmission channel and a signal source to which said termination resistor is connected.

6. A semiconductor module according to claim 1, wherein said termination resistor's form of termination is selected from a group consisting of: parallel termination, Thevenin termination, series termination, AC termination, and Schotty-diode termination.

7. A semiconductor module according to claim 1, wherein said termination resistor is thermally coupled to said heat spreader.

8. A semiconductor module according to claim 1, wherein said termination resistor is bonded directly to a side wall of said heat spreader.

9. A semiconductor module according to claim 1, wherein said two semiconductors are mounted on opposing side walls of said heat spreader.

10. A semiconductor module according to claim 2, wherein each of said semiconductors are bonded directly to said side wall of said heat spreader.

11. A semiconductor module according to claim 1, wherein said leads form part of a flexible circuit at least partially attached to said heat spreader.

12. A semiconductor module according to claim 11, wherein said flexible circuit is a flexible dielectric tape.

13. A semiconductor module according to claim 12, wherein said flexible circuit is bonded directly to said side wall of said heat spreader.

14. A semiconductor module according to claim 1, wherein said common electrically conductive lead is selected from a group consisting of a voltage supply node, a reference voltage node, and an electrical ground node.

15. A semiconductor module according to claim 1, wherein said heat spreader is a solid block of heat dissipating material.

16. A semiconductor module according to claim 1, wherein said heat spreader is “u” shaped.

17. A method of making a semiconductor module, comprising:

providing a plurality of electrically conductive leads;

electrically coupling at least two semiconductors to said plurality of electrically conductive leads, where at least one of said electrically conductive leads is common to both of said semiconductors;

thermally coupling said semiconductors to a heat spreader; and

electrically coupling a termination resistor to at least one of said semiconductors.

18. A method according to claim 17, initially comprising electrically coupling said semiconductors in series, where said semiconductors are capable of being electrically coupled to a transmission channel.

19. A method according to claim 17, further comprising electrically coupling an additional termination resistor to the semiconductor not already connected to said termination resistor, where each of said semiconductors is capable of being electrically coupled to a separate transmission channel.

20. A method according to claim 17, including bonding said termination resistor directly to a side wall of said heat spreader.

21. A method according to claim 17, including mounting said two semiconductors on opposing side walls of said heat spreader.

22. A method according to claim 17, including bonding each of said semiconductors directly to a side wall of said heat spreader.

23. A method according to claim 17, wherein said leads form part of a flexible circuit at least partially attached to said heat spreader, said method including bonding said flexible circuit directly to a side wall of said heat spreader.

24. A semiconductor module, comprising:

a heat spreader comprising a first vertical member spaced apart from a second vertical member and a horizontal member joining the first vertical member and the second vertical member to define an inverted channel between the first and second vertical members;

at least two semiconductors each containing integrated circuitry, wherein each semiconductor of the semiconductors is thermally coupled to a respective one of the first and second vertical members;

a flexible circuit bonded to at least a portion of a surface of the inverted channel defined by the heat spreader, wherein the flexible circuit is electrically coupled to the semiconductors; and

a plurality of electrical contacts including a first set of electrical contacts disposed on a portion of the flexible circuit that is proximate to an end of the first vertical member and is remote from the horizontal member, and a second set of electrical contacts disposed on a portion of the flexible circuit that is proximate to an end of the second vertical member and is remote from the horizontal member, wherein the plurality of electrical contacts are configured so that a signal enters at the first set of electrical contacts and exits at the second set of electrical contacts.

25. The semiconductor module of claim 24, wherein the flexible circuit is flexible tape.

26. The semiconductor module according to claim 24, further comprising a termination resistor electrically coupled to the integrated circuitry of at least one of the semiconductors, where the termination resistor is thermally coupled to the heat spreader.

27. The semiconductor module of claim 26, further comprising one or more additional termination resistors, wherein each respective semiconductor contains integrated circuitry that is electrically coupled to a distinct termination resistor.

28. The semiconductor module according to claim 26, wherein one semiconductor of the semiconductors is not connected to the termination resistor, and an additional termination resistor is electrically coupled to the one semiconductor not connected to the termination resistor.

29. The semiconductor module according to claim 26, wherein a resistance value of the termination resistor is selected such that an impedance of the termination resistor substantially matches an impedance of a transmission channel and a signal source to which the termination resistor is connected.

30. The semiconductor module according to claim 26, wherein the termination resistor is thermally coupled to the heat spreader.

31. The semiconductor module according to claim 26, wherein the termination resistor is bonded directly to a side wall of the heat spreader.

32. The semiconductor module according to claim 24, wherein the heat spreader has an inverted “u” shape.

33. The semiconductor module of claim 24, further comprising a fastening mechanism for removeably anchoring the semiconductor module to a circuit board.

34. The semiconductor module of claim 33, wherein the fastening mechanism includes clamps.

35. The semiconductor module of claim 24, wherein the plurality of electrical contacts are an array of bond pads.

36. The semiconductor module of claim 24, wherein the plurality of electrical contacts are an array of metal points.

37. The semiconductor module of claim 24, wherein the semiconductors are bonded to the heat spreader using a bonding adhesive with thermal expansion properties similar to those of the semiconductors and the heat spreader.

38. The semiconductor module of claim 24, wherein the flexible circuit contains a plurality of electrically conductive leads.

39. The semiconductor module of claim 24, wherein at least portion of the flexible circuit that is bonded to the heat spreader is bonded using a bonding adhesive with thermal expansion properties similar to those of the flexible circuit and the heat spreader.

40. The semiconductor module of claim 24, wherein the portion of the flexible circuit that is bonded to the heat spreader is also bonded to the semiconductors.

41. The semiconductor module of claim 24, wherein the semiconductor module is configured to connect to a pin grid array (PGA) socket that in turn connects to a circuit board.

42. The semiconductor module of claim 24, further comprising shielding to protect the semiconductors from electromagnetic interference.

43. The semiconductor module of claim 24, wherein the two or more semiconductors are connected to one another by electrical leads in the flexible circuit.

44. The semiconductor module of claim 24, wherein the semiconductor module is a memory module.

45. The semiconductor module of claim 24, wherein each semiconductor is connected to a distinct transmission channel and each transmission channel is separately terminated.

46. The semiconductor module of claim 24, wherein the first and second vertical members of the heat spreader are substantially perpendicular to the circuit board when the plurality of electrical contacts disposed on the flexible circuit are removeably coupled to the corresponding electrical contacts on the circuit board.

47. The semiconductor module of claim 24, wherein a signal path length from a first semiconductor to the first set of electrical contacts is substantially the same as a signal path length from a second semiconductor to the second set of electrical contacts.

48. The semiconductor module of claim 47, wherein a distance between the first set of electrical contacts and the first semiconductor is substantially equal to a distance between the second set of electrical contacts and the second semiconductor.

49. The semiconductor module of claim 24, further comprising:

a first base member joined to an end of the first vertical member that is not joined to the horizontal member, wherein the first set of electrical contacts are disposed on a portion of the flexible circuit that is coupled to the first base member; and

a second base member joined to an end of the second vertical member that is not joined to the horizontal member, wherein the second set of electrical contacts are disposed on a portion of the flexible circuit that is coupled to the second base member.

50. The semiconductor module of claim 49, wherein the first base member and the second base member are parallel to the horizontal member and remote from the horizontal member.