[Discuss] PC Build

[blu at nedharvey.com (Edward Ned Harvey (blu))]

> From: Discuss [mailto:discuss-bounces+blu=nedharvey.com at blu.org] On
> Behalf Of Steve Litt
> 
> "dry build" it outside the case first

Woah - that's a terrible idea. When you screw the motherboard down to the case, you'll see that some of your anchor points are nonconductive and ok to anchor using nonconductive materials (little plastic snaps) but some of your anchor points are lined with brass or aluminum, and must be screwed down to ensure multiple points of ground.

Yes, of course, your motherboard will be grounded by the ground wire in the power harness, but something people often don't realize is that the speed of light crossing the distance of the CPU is actually significant - You've got a CPU doing 3 * 10^9 instructions per second, and the speed of light is 3 * 10^8 m/s. Which means light travels 10cm in the period of time your CPU does each instruction. So if some particular instruction gobbles a bunch of power and dumps it onto ground, those electrons haven't even had time to reach the ground yet. So you get a noisy ground.

The manufacturers of your CPU and motherboard have to contend with individual wires interfering with each other by capacitance, inductance, and RF burst. They put multiple ground points on the motherboard for a reason.


> Obviously, use static protection. I'm not going to tell you to wear a
> wrist strap, because that can put you in danger in a shock situation,
> but certainly touch the case every few seconds, and never walk across
> the floor holding a part, and when you've been walking, touch the case
> before anything else.

Don't touch the case every few seconds. Touch the case literally constantly (never let your hand leave the case) as long as your other hand is touching any of the electronics. The main purpose of the strap is to ensure 100% constant contact with the case, while enabling both hands free. You don't have to worry about getting shocked, if you remove the strap every time you connect power. These two should be mutually exclusive.

Of course, touching the case does precisely jack shit, if you have your motherboard not inside the case, or not grounded to the case. The thing that matters is NOT that you're in static equilibrium with the case. The thing that matters is that you're in static equilibrium with the electronics. Normally we solve this problem by grounding the electronics to the case, and then touching the case (or wiring ourselves to it.)

There's the catch-22 of "How do I get the electronics into the case without touching them first?" Keep the electronics in the antistatic bag, set it on the antistatic mat, touch both the case and the electronics with your hand for a few seconds to slowly discharge any static. Carefully remove the electronics from the bag, touching *only* designated ground contacts. So your body is always in static equilibrium with the frame of reference that the electronics consider to be ground.

Normally, ESD is not a static shock lightning bolt; normally it's not even something you can feel or see. It's also not normally something you notice after you power on the device. Normally, ESD is very subtle, like you just reached across the table and in doing so your clothes rubbed on each other and created a static charge in your body, which degraded the life of one transistor somewhere in some chip. It only takes a few volts to exceed the specs of your device and cause damage, whereas it takes like 20,000 volts to generate a spark. So the symptom of *typical* ESD, which most people don't notice, is a shorter system life and/or increased flakiness. Only the most dramatic and extreme ESD results in a catastrophic failure, where some chip is rendered instantly nonfunctional.