Methods and electronic board products utilizing endothermic material for filling vias to absorb heat during wave soldering

• US 6,651,869 B2
• Filed: 09/21/2001
• Issued: 11/25/2003
• Est. Priority Date: 09/21/2001
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Aspandiar, Raiyomand F., Pearson, Tom E., Combs, Christopher
• Primary Examiner(s): Dunn, Tom
• Assistant Examiner(s): EDMONDSON, LYNNE RENEE
• Application Number:
  US09/957,532
• Publication Number:
  US 20030057265A1
• Time in Patent Office: 795 Days
• Field of Search: 228/260, 228/37, 228/36, 228/216, 228/259, 228/180.1, 228/175, 228/180.22, 228/215, 174/263-265
• US Class Current: 228/180.21
• CPC Class Codes: B23K 1/085 Wave soldering
• CPC Class Codes: B23K 1/20 Preliminary treatment of work or areas to be soldered, e.g. in respect of a galvanic coating preparation of surfaces in particular ways, see the relevant classes for the treatments or the materials treated, e.g. C04B, C23C
• CPC Class Codes: B23K 2101/42 Printed circuits
• CPC Class Codes: B23K 3/085 Cooling, heat sink or heat shielding means
• CPC Class Codes: H05K 2201/0129 Thermoplastic polymer, e.g. auto-adhesive layer; Shaping of thermoplastic polymer
• CPC Class Codes: H05K 2201/0959 Plated through-holes or plated blind vias filled with insulating material
• CPC Class Codes: H05K 2201/10734 Ball grid array [BGA]; Bump grid array
• CPC Class Codes: H05K 2203/0455 PTH for surface mount device [SMD], e.g. wherein solder flows through the PTH during mounting
• CPC Class Codes: H05K 2203/0776 Uses of liquids not otherwise provided for in H05K2203/0759 - H05K2203/0773
• CPC Class Codes: H05K 2203/122 Organic non-polymeric compounds, e.g. oil, wax, thiol using solvent H05K2203/0783
• CPC Class Codes: H05K 3/3436 having an array of bottom contacts, e.g. pad grid array or ball grid array components
• CPC Class Codes: H05K 3/3468 Applying molten solder
• CPC Class Codes: H05K 3/3494 Heating methods for reflowing of solder using integral heating means H05K1/0212
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A method of wave soldering a circuit board while avoiding reflow of a solder joint on the topside of the board from heat conducted from the solder wave through at least one via in the board in heat conducting relation with the topside solder joint, comprises subjecting the circuit board to a solder wave and absorbing heat being conducted from the solder wave through the at least one via with an endothermic material in the via hole which undergoes a heat absorbing reaction. The heat absorbing reaction of the endothermic material is preferably a phase change, such as melting. The melted endothermic material is retained in the via hole during wave soldering by capillary forces and a cap on the lower end of the via hole. A disclosed method of making the circuit board includes locating the endothermic material in the via hole by inserting a preform of the endothermic material into the via hole or hot dispensing the endothermic material into the via hole. An electronic board product for practicing the method/made by the method is also disclosed.

Claims

1. A method of wave soldering a circuit board having a solder joint on the topside of the board and at least one through via in the board formed by electrically conductive plating in a via hole, the via being in heat conducting relation with the topside solder joint, the method comprising:

subjecting the circuit board to a solder wave; and

absorbing heat conducted from the solder wave through the at least one via with an endothermic material located within the via hole which undergoes a heat absorbing phase change to heat being conducted from the solder wave through the at least one via during wave soldering.

2. The method according to claim 1, wherein the phase change is melting.

3. The method according to claim 2, further comprising solidifying the melted endothermic material in the via hole when the temperature reduces after wave soldering to cause the endothermic material to give up the heat it absorbed during the wave soldering.

4. The method according to claim 2, including retaining the melted endothermic material in the via hole.

5. The method according to claim 4, wherein the melted endothermic material is retained in the via hole by a cap over the lower end of the via hole.

6. The method according to claim 4, wherein the melted endothermic material is retained in the via hole by capillary forces.

7. The method according to claim 1, further comprising retaining the endothermic material in the via hole after it undergoes the heat absorbing phase change.

8. The method according to claim 1, wherein the endothermic material undergoes the heat absorbing phase change in the temperature range of 50°

C. to 200°

C.

27. The method according to claim 1, wherein the endothermic material is selected from the group consisting of gutta-percha, iodides, and waxes, and has a melting temperature in the range of 50°

C. to 200°

C.

30. The method according to claim 1, wherein the via hole has a diameter less than 22 mils.

9. A method of making a circuit board comprising:

providing a circuit board having at least one via formed by electrically conductive plating in a via hole, the via extending through the circuit board in heat conducting relation with a surface mount pad on the topside of the board; and

locating an endothermic material in the via hole of the via, the endothermic material having a characteristic of undergoing a heat absorbing phase change to heat being conducted from a solder wave through the via during wave soldering of the circuit board.

10. The method according to claim 9, including capping the lower end of the via hole to retain the endothermic material therein during wave soldering.

11. The method according to claim 9, wherein the locating includes inserting a preform of the endothermic material into the via hole.

12. The method according to claim 9, wherein the locating includes hot dispensing the endothermic material into the via hole.

13. The method according to claim 9, further comprising surface mounting a component to the pad on the topside of the circuit board after the endothermic material is located in the via hole.

14. The method according to claim 13, wherein the component mounted on the topside of the board on the pad is a ball grid array component.

15. The method according to claim 9, wherein the at least one via is located in the pad on the topside of the board.

16. The method according to claim 9, wherein the at least one via is located between adjacent pads on the topside of the circuit board.

17. The method according to claim 9, wherein the phase change is melting.

18. The method according to claim 9, including filling the via hole with the endothermic material.

28. The method according to claim 9, wherein the endothermic material is selected from the group consisting of gutta-percha, iodides, and waxes, and has a melting temperature in the range of 50°

C. to 200°

C.

31. The method according to claim 9, wherein the via hole has a diameter less than 22 mils.

19. An electronic board product comprising:

a circuit board having at least one via formed by electrically conductive plating in a via hole, the via extending through the circuit board in heat conducting relation with a pad on the topside of the board;

a component which is mounted by way of a solder joint to the pad on the topside of the board; and

an endothermic material located in the via hole of the via, the endothermic material having a characteristic of undergoing a heat absorbing phase change to heat being conducted from a solder wave through the via during wave soldering of the circuit board.

20. The electronic board product according to claim 19, further comprising a cap over the lower end of the via hole to retain the endothermic material therein during wave soldering.

21. The electronic board product according to claim 19, wherein the endothermic material fills the via hole.

22. The electronic board product according to claim 19, wherein the component is a ball grid array component which is mounted to the pad on the topside of the board by way of the solder joint.

23. The electronic board product according to claim 19, wherein the electronic board product is a mother board.

24. The electronic board product according to claim 19, wherein the electronic board product is a server board.

25. The electronic board product according to claim 19, wherein the phase change is melting.

26. The electronic board product according to claim 19, wherein the endothermic material undergoes the heat absorbing phase change in the temperature range of 50°

C. to 200°

C.

29. The electronic board according to claim 19, wherein the endothermic material is selected from the group consisting of gutta-percha, iodides, and waxes, and has a melting temperature in the range of 50°

C. to 200°

C.

32. The electronic board according to claim 19, wherein the via hole has a diameter less than 22 mils.