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Method for a wave-soldered structural reinforcement solution for motherboard chipsets

IP.com Disclosure Number: IPCOM000008377D
Publication Date: 2002-Jun-11
Document File: 5 page(s) / 116K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a wave-soldered structural reinforcement solution for motherboard chipsets. Benefits include improved thermal performance.

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Method for a wave-soldered structural reinforcement solution for motherboard chipsets

Disclosed is a method for a wave-soldered structural reinforcement solution for motherboard chipsets. Benefits include improved thermal performance.

Background

              As microprocessor speed increases, the cooling requirement increases and the mass of CPU heatsinks continues to increase. A mass of 450g is typical of an ATX motherboard architecture. The ball grid array (BGA) to board interconnect of the chipset (next to the CPU) is being damaged from shock and vibration due to severe board flex.

              To mitigate the damage to the chipset interconnect, a structural reinforcement solution is required to reduce the amount of board flex and stress to the chipset and BGA solder joints. This task is complicated by the fact that the CPU/chipset core is the area with the highest trace density. Dedicating keep-outs (component or trace) to a mechanical solution typically causes the board layer count to increase, effectively pricing the motherboard out of the competitive market.

              The heat from the chipset must be dissipated by a thermal solution. A structure that cannot be a platform is not useful in the motherboard core area.

              Conventionally, a popular drop-in mechanical solution for motherboards is the addition of stiffening bars. They are essentially small I-beams that are wave soldered to the board through-holes at regular intervals. These bars are placed at strategic locations and orientations on the board to reduce deflection in selected directions. The stiffening bars, however, drastically change and constrain component placement. In addition, the regular through-holes required are large. In the typical desktop motherboard architecture, stiffening bars are not feasible. They are mainly used in workstation and server segments that already have high layer-count boards.

              Stiffening plates and load-transfer plates are common (see Figure 1). These conventional solutions attach a plastic or metal plate to the backside of the motherboard in the CPU/chipset core area. They are typically attached to the motherboard by rivets and require relatively large through-holes that are difficult to accommodate. Both solutions require access to the backside of the motherboard and a backside assembly step during manufacturing. Backside assembly is not a process that typically occurs in desktop-motherboard manufacturing and can increase assembly cost, depending on assembly-line design.

              Stiffening plates usually have sufficient stiffness to reinforce the motherboard. Load-transfer plates capture the motherboard and lock to a point in the chassis for mechanical stiffening. Load transfer plates are additionally limited because motherboard and chassis design must be coordinated and tooled. Load transfer plates are typically only an option for systems manufacturers that control the design of their own boards and chassis.

              Another conventional solution is a compressive preload. This solution puts the BGA u...