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Method for rapid cure of thermoset heatsink adhesive using hotplate preheating

IP.com Disclosure Number: IPCOM000007145D
Publication Date: 2002-Feb-27
Document File: 5 page(s) / 86K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for rapid cure of thermoset heatsink adhesive using hotplate preheating. Benefits include improved reliability and improved thermal performance.

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Method for rapid cure of thermoset heatsink adhesive using hotplate preheating

Disclosed is a method for rapid cure of thermoset heatsink adhesive using hotplate preheating. Benefits include improved reliability and improved thermal performance.

Background

              High-speed microprocessors generate heat, which is conventionally dissipated by a heatsink. It must be attached quickly and inexpensively with minimum material cost, and with maximum quality and reliability.

              Thermoset heatsink adhesives, such as epoxies and silicones, have significant advantages over other thermal interface materials (TIMs) and attachment methods. Thermoset adhesives fulfill the dual function of being mechanical bonding materials in addition to TIMs. With greases and gels, clips or other mechanical attachments are required. These clips must be attached using holes in the printed circuit board (PCB). These holes take up space that could otherwise be used for trace routing on all circuit layers. Thermoset heatsink adhesives that cure thermally are stronger than adhesives that cure anaerobically. Thermally cured adhesives also have a significantly higher shear and tensile strength than two-part adhesives cured at room temperature.

              High-volume continuous-flow board assembly operations (such as PC motherboard assembly) have been unable to employ thermoset adhesives. Curing them thermally has required that the entire PCB assembly be heated to elevated temperatures for some significant amount of time, such as 30-60 minutes. Such a lengthy process step is very difficult and expensive to implement in an assembly operation. The thermal excursion can cause deleterious material effects in components, solder joints, and PCBs.

              The problem is conventionally addressed by a variety of solutions:

•             Use of greases or gels that do not require thermally activated or any other type of curing but do require clips or other mechanical attachments to hold the heatsink on the component

•             Use of adhesives that cure anaerobically

•             Use of thermoset adhesives that are thermally cured by placing the entire printed circuit board assembly in an oven at the specified temperature for the required time period (see Figure 1)

              Attachment with an oven-cured thermoset adhesive can be performed using the following steps:

1.           Attach the component to the board.
2.           Apply the thermoset adhesive to the component.
3.           Set the heatsink onto the adhesive.
4.           Place the entire PCB in an oven.
5.           Heat the oven to the required degree for the specified time period.

              Attachment with a TIM and a separate mechanical attachment method can be performed using the following steps:

1.           Attach the component to the board.
2.           Apply the TIM (such as gel or grease) to the component.
3.           Place the heatsink with the retention clip on top of the gel or grease.

4.           Attach the heatsink to the board holes or anchors (mounted in holes), clamping the board/ component/TIM/heatsink between the board and the heatsink clip (see Figure 2).

      A hotplate is a dev...