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Comment by mi100hael | Hacker News Reader

    > In order to read the NVMe, I therefor developped a PCIe card with a Zero
    > Insertion Force reader. I brought the JTAG part to 20pin header. The hard
    > pard in here is the signal integrity of the differential pairs. In order
    > to do so, I had to use multi layer PCB, and have the impedence match by
    > knowing the stackup, materials used for prepeg and so on..

Posts like this are very humbling. They serve as a good reminder that no matter how far I've come and how much I've learned, there will always be someone out there who knows vastly more than me like the back of their hand.

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Don't feel too bad.

Fully understanding the complete stack of a modern computer system is outside the scope of almost everyone. These things are complicated and we've built abstractions, interfaces and modules to manage the complexity.

People specialize in their own fields. I am trained in digital integrated circuit design, but don't ask me to build a file system.

Exactly. This is super impressive work, but also very specialized. Even for non-EE majors, most IT people could at least understand the basics of what he was doing.

This side of the business is actually pretty straightforward to learn and be guided by your PCB assembly house and design software. Ask the PCB fab for the stackup, punch 90 ohms into the calculator, and get a number in mils for the PCB software.

And the dirty secret is that for short runs, testbeds and hacking tools you can often cheat on the controlled impedance a bit to produce abominations like USB-over-FFC and three-ended ethernet cables.

Now, hot air rework, that's a serious manual skill that I respect.

(I suppose the difference versus learning software development work is that failures are expensive...)

> Ask the PCB fab for the stackup, punch 90 ohms into the calculator, and get a number in mils for the PCB software.

This sounds like gibberish to me.

(I know it's not, just that the notion that it's "straightforward to get into" is maybe off the mark.)

The stackup is what controls the layers of a bare PCB; signal, power, ground, etc [1]. An engineer at your board supplier is likely involved in determining the stackup with the EE and PCB designer. The stackup and material selection of the bare board is one of the things that controls min/max trace width, proximity, etc. Once you have that info, you can plug it into your CAD tool of choice, for instance in Mentor Xpedition it's CES [2]. Makes things like differential pairs a lot easier.

1. http://blog.optimumdesign.com/hdi-layer-stackups-for-large-d...

2. https://www.mentor.com/pcb/xpedition/constraint-manager/

Good SMT rework is 60% flux, 20% isopropyl alcohol, 10% magnification and 10% practice. The trick is surface tension - if the surfaces are properly wetted, surface tension pulls the part into alignment as if by magic. Achieving good wetting is as simple as getting the solderable surfaces spotlessly clean and deoxidized, then using copious amounts of flux. If your preparation is good, the parts almost solder themselves.

Fine-pitch BGA rework can be genuinely challenging, but the core skills are remarkably straightforward. A complete novice can rework QFNs and 0603 passives with very little practice if they're taught the correct techniques. I actively prefer working with SMT over through-hole.

I teach a course (at various hacking events) titled "Surface mount electronics assembly for terrified beginners" and the thing that basically every participant reports after is that they expected it to be harder. We go from "never knowingly touched a PCB" down to 0.5mm pitch QFNs and 0402 passives in the space of an hour or so, so what you're saying about novices is absolutely correct. (if you want a course like that near you, contact me)

All these things are just different worlds. I'm the same when it comes to medicine or tree surgery or a multitude of different things. I have no idea how a security guard even works!

On this subject though, I did EE in the past and now software and it's roughly as complicated as throwing some code together after a few years of practice. Except that the design rules, physics and CAD software are perhaps ironically somewhat better defined than what the software industry has managed! Many an EE has looked in awe at the software that we write too.

It's not even that hard, I managed to design a simple PCB after only a few months of tinkering with hardware. It's really not bad, and very fun. I recommend it to everyone.

I enjoy PCB design too - through it results in me spending an inordinate amount of time tweaking trace placement and ground planes for mostly aesthetic purposes :)

That is 90% of the fun :P

Recommended too.

For one-offs you can entirely forgo the PCB design if you so desire as well and just use the PCB stock and rats nest it.

One of my creations: http://imgur.com/mcS79lU - fugly but very robust, functional, free of nasty parasitics and from paper to powered up and working is around 20 minutes work.

> I have no idea how a security guard even works!

Hm. Can someone shed some light on this?

I bet he plays jazz piano too.

That's the bread and butter of digital EEs. In fact a digital EE would be very happy if all he had to do was a 4 layer board with a single 70 ball chip :)

The layout here shouldn't be difficult at all - but the other feats are quite impressive, still :)

Some big words mixed in there, but if you try your hand at this I think you'd find that making impedance-controlled differential traces on a PCB isn't much of a trick at all. It's a difficult engineering challenge if you intend to mass produce, but it's not a challenge if you intend to make 10 boards and you aren't cost sensitive and you don't care if 9 boards don't work.

I help design PCIe cards and interfaces, and this guy's work is blowing my fucking mind.

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