lördag 26 januari 2008

Why laptop computers keep on failing - the Ball Grid Array problem

The BGA is a popular method of attaching integrated circuit packages to printed circuit boards. The IC package has one face covered (or partly covered) with balls of solder in a grid pattern.

The printed circuit board has copper pads in a pattern that matches the solder balls. The assembly is then heated, either in a heater, or special oven, melting the solder balls and forming conductive connections.

Because of surface tension, the molten solder holds the package in alignment with the circuit board, at the right distance, while the solder cools and solidifies.

Whilst there are advantages, there are also snags. The main ones are that the solder balls cannot bend, for example if the components expand due to warming, or flex due to movement, for example, in a laptop computer which is moved around. The joints are therefore liable to break, and the problem is compounded due to the recent adoption of lead-free solder, which is more brittle. The system is also makes for difficulties in inspection, fault-tracing and repair.

These factors seem to be behind the crop of failures that have affected many makes of laptop computer.

Matters should improve with better lead free solders and the shrinking size of components, but if you have a laptop computer of between 2004 and 2006 vintage, don't be surprised if it proves troublesome.

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