Motherboard Design Process

MBRFan writes "MBReview has posted the latest revision of their 'Motherboards - The Designing Process' article. This article covers the design process for modern motherboards, and also goes over some of the most common components that can be found. Definite read for information lovers, though beware, it'll take a while to read!"

Comments

Not bad, but

[jimmyswimmy]

I used to design motherboard power system components, and the author spends a good bit of time talking about that. That is actually the most complicated part of the board design, as it is not at all automated. Most component vendors try to sell a complete solution to the motherboard vendor, easing their job somewhat while helping the sales of the component vendor.

One particularly interesting item of note: all those capacitors the author describes are absolutely crucial, and together form one of the largest cost items on the board. The system is tested using a processor-vendor-supplied "load tool" which simulates the worst case load transients one can ever expect to see. Most of that testing is done by the power system component vendor and then provided as a block to the motherboard vendor. Most motherboard vendors have no idea what they are doing there.

In fact, a lot of the foreign manufacturers (no names) cost-reduce their designs by simply pulling out caps until the system blue screens. Then they put the last one back in and sell it. Intel is the only manufacturer I am aware of that actually sells the worst-case performing design.

Note that I am only aware of products related to Intel-type motherboards. I never worked on the othe stuff.

Re:Not bad, but

[jimmyswimmy]

As another poster pointed out, until a complete shift in technology occurs, this will not happen. Power loss in a wire follows the law P=VI. The lower the CPU supply voltage, the higher the input current will be.

We continue to move to higher CPU switching frequencies and lower CPU voltages. Why? Well, higher frequency means higher clock speed, and greater processing power. Another way to increase processing power is to add complexity to the circuit, which means a larger chip. BUT, you can reduce the size of the chip by reducing the size of the features required to implement your changes. And that, my friend, means you need a lower voltage, or you will destroy those tiny, delicate features (breakdown the MOS gate oxide layer).

The relationship between power loss, switching frequency, and voltage, is straightforward:

P = C*V*f

You can't really work that out for a modern CPU but it is illustrative.

And with upwards of 100 A at less than 1.5V driving your CPU, motherboards will have an onboard VR (voltage regulator) for years to come. I used to test with an old ATX supply (before the ATX 2.0 spec added the tiny 2x2 12 V connector) and after pulling 12 A through the single wire supplying 12 V for fifteen minutes, the insulation became brittle and browned. You would need to more than double your existing wires just for DC... and don't get me started about all those capacitors again!

I've heard stories...

[Silverlancer]

I've heard stories of crappy motherboards blowing capacitors. Which is why its always better to get the 150 dollar one than the 30 dollar one. Because the 30 dollar one is effectively made out of scrap metal...

Re:I've heard stories...

[Anonymous Coward]

Nonsense! The capacitor issue you are talking about was due to defective manufacture of the capacitors. I see the effects to this day.

The thing is, capacitor failures were not limited to "cheap" motherborads! Although the more expensive boards may have had more effort in terms of worst-case design or more parts added to increase timing/noise margins, in the end they all send it overseas to be manufactured and those guys go out and buy the cheapest parts they can find. For a while, those were the badly manufactured capacitors mentioned above.

I reiterate: I have seen these capacitor failures in motherboards from major players as well as all the cheaper motherboard manufacturers. Buying a $150 dollar motherboard rather than a $30 one does not necessarily guarantee reliability.

Re:It would have been interesting

[bsd4me]

PC motheboards aren't terribly complicated as far as PWBs go. The don't really have a lot of components, and they don't have a lot of layers.

What is interesting about them, but I don't think it really complicates the manufacturing proces, is the effort that goes into reducing the number of layers (number of layers is directly related to cost). This compilcates both routing and signal integrity.

Re:Maybe someday they could get it right.

[Timesprout]

How does crap like this get modded insightful? There are many factors involved in a production process such as motherboards. In many cases trade offs will have to be made between engineering, manufacturing and cost. If the AC who feels maufacturers are not doing the job properly may I suggest he/she/it puts forward a better design than can be mass produced and afforded by the general population

Doesn't make sense to most people

[Anonymous Coward]

IANAMBD, but...

"trace" == Metal tracks carrying the current

"Prepreg" == insulating "silk" layer separating the metal tracks running above and below.

"static impedance" == "guess" they mean parasitic capacitances formed between the tracks crossing over each other, separated by the "Prepeg".

"Er, or dielectric constant" == See physics book for parallel plate capacitor, the 'E' is the "greek epsilon"

"height of the trace" == the plate separation ... I.e the thickness of the "Prepeg"

.

The guy who wrote this article has a glittering career in the Patent business.

FYI, 1 mils = 2.54e-05 metre

[joostje]

To save the other metric readers the trouble googling, 1 mils = 1/1000 inch = 2.54e-5 metre. conversion