Re: Soldering bypass caps to QFP possible?
- From: Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 26 Jan 2008 17:09:18 GMT
John Larkin wrote:
On Sat, 26 Jan 2008 01:55:57 GMT, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:
John Larkin wrote:On Fri, 25 Jan 2008 23:43:13 GMT, JoergBoth, but mostly because the micro often dies during thunderstorms.
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:
Ok guys, got a client's system here, to see what can be done to save the day. Among other (easier) things I discovered a serious layout booboo. The usual, opened up the Gerbers and my toe nails curled. Too late for a relayout at this point, must be reworked :-(
Is it reasonably possible to solder a bypass cap to adjacent pins on a 0.5mm pitch QFP chip or would that just open up a can of worms? Shorts, opens, etc. I mean, can a good rework house do that reliably, in your experience (not by what they'd tell me)? To throw another curve, these boards are clear-coated.
And no, I did not do that layout ;-)
Does it need bypass caps? For emi compliance, or just to work?
Can't they be kluged on the board somewhere?Nope. The next pair of vias and the lone bypass cap is two furlongs down the fence.
I'm guessing that some skilled person could solder 0201 caps acrossPossibly, although 01005 may be better in order for the solder to wick up properly. But I'd need some serious capacitance there, at least 0.1uF. 0201 comes in that capacitance range and 6.3V is enough, even 4V would.
those pins. I think maybe even I could. I've been soldering some
really outrageously tiny stuff this week. The coating would have to be
scraped off, of course.
You could certainly solder wires and run them up to 0402's right onMaybe we have to, as long as the reowrk shops are able to.
top of the chip.
How many boards did they build?About 2500 :-(
YIKES!
What WERE they thinking?
You have your own R&D plus manufacturing so designs have to exceed the Larkin quality threshold before they go into production. So you know it's all good. But when you are consulting stuff like this is a fairly common thing you'd see :-(
Sometimes I have clients who want a new design from scratch. Others come with existing ones that plain don't work. Consulting is like architects and building contractors in one person. We get to design/build someone's dream home but we also have to restore flood or fire damage. In many cases we have to serve a company specialized in their field but not electronics. And if problems creep up they often don't after some substantial field exposure. For example storms only happen during a very short season and the usual ESD pistol tests at TUEV or UL won't reveal too many problems up front (it passed all those).
Definitely make a small pc board to glue on top of the chip, with
little wires hanging down, to solder to the ic pins.
Sort of like this one:
ftp://66.117.156.8/883A.jpg
I might have to :-(
--
Regards, Joerg
http://www.analogconsultants.com/
.
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