[Oberon] Updated RiskFive FOM schematics

Skulski, Wojciech skulski at pas.rochester.edu
Wed Jan 17 03:07:30 CET 2018

Paul Reed wrote:

> On the other hand, I've watched with interest and admiration as what is
> now called the "maker" community grapples with the unavailability of
> through-hole parts.  They even have great success hand-soldering ball-grid
> array chips these days.  Maybe the way forward is to use SMD, but design
> for hand-re-workability wherever possible.

I assembled most of my prototypes by hand, including QFN parts with 0.5 mm spacing and a ground pad hidden under the chip. An interesting exercise was soldering power nano modules whose pads are entirely under the chip (part number LMZ10500SIL, take a look at the data sheet). Another interesting exercise was AD9650, which is a QFN part costing about $150 a piece. With time and practice I became pretty good at this kind of assembly, though reworking 0201 parts gives me goosebumps. If you ever looked at these then you will know what I mean. 

I would never assemble a BGA myself. I witnessed a couple horror stories in the university lab equipped with professional tools, but without proper infrastructure. After watching the failures I know where to stop tinkering and when to turn to professional services. Some reflow processes require nitrogen gas flow, for example. I would not try this at home using a toaster oven. I would not try BGAs with a chinese reflow oven, which I have used for the QFN assembly. It is a fine device which I used more than once. But one has to know where to stop. 

 I have had my share of disappointments with some American assembly houses, including one from Silicon Valley whose name I do not even want to mention. I have had a horrific experience with the original manufacturer of the BeagleBone. They went bankrupt soon after they screwed up my boards. 

RiskFive boards will be assembled professionally. I have had good experience with chinese companies. Their work is reasonably priced and they are very professional. There are number of fine companies out there who focus on short runs. I have had good experience with these. I will use their services again.


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