Richard Cownie (tich@pobox.com) on 9/18/09 wrote:
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>My point was that the *motherboard* itself is not rigid,
>and indeed will expand and contract and distort in
>various ways. It's not obvious that attaching an
>expanding and contracting motherboard to a rigid case
>is the best way to reduce stress and minimize failures.

First, the primary methods of preventing cracking due to thermal expansion are the use of thick PCBs which are more rigid and resistant to warp, epoxy underfills which adhere packages to boards, and tensioned heatsinks which put pressure on a package. Reducing stress doesn't come in the form of, "just let it bend and twist as it wants to."

Second, I never said that directly screwing a motherboard to a flexible or rigid chassis is a good idea. I said that mechanical isolation is desirable, and that a rigid chassis in conjunction with mechanical isolation is superior to a flexible chassis in regards to reducing stress caused by picking-up and moving the laptop around.


>It isn't even obvious that the rigid case helps you
>when you drop the machine. After all, the way you build safe cars is not to have a rigid structure, but to have
>crumple zones that can absorb the energy of an impact
>without causing excessively high deceleration to the
>fragile stuff inside.

Yes - mechanical isolation. However, you are conflating the rigidity of a chassis with it's durability under point, shock stresses. I'd probably prefer an aluminum chassis if dropped, anyway:

http://i.gizmodo.com/5215296/unibody-construction-helps-macbook-air-survive-plane-crash


>What's definitely true is that the solid aluminum case
>*feels* nice, and *looks* nice, and the lack of flexing
>and squeaking is reassuring. But that's about psychology
>and marketing, not actual reliability ... like the
>leather seats in business class.

Business class is personally worthwhile because there's a heavily reduced risk of being placed next to a crying baby.


>Aha! All failing at the same rate is about what I would
>expect, when the chips are all the same, and the
>motherboards and disks come from the same few suppliers
>in China and Taiwan.

What we are missing is the reason that each system was brought-in.