Re: Soldering bypass caps to QFP possible?

John Larkin wrote:
On Fri, 25 Jan 2008 23:43:13 GMT, Joerg
<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?


Both, but mostly because the micro often dies during thunderstorms.


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 across
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.


Possibly, 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.


You could certainly solder wires and run them up to 0402's right on
top of the chip.


Maybe we have to, as long as the reowrk shops are able to.


How many boards did they build?


About 2500 :-(

--
Regards, Joerg

http://www.analogconsultants.com/
.

Relevant Pages

  • Re: Soldering bypass caps to QFP possible?
    ... Among other things I discovered a serious layout booboo. ... Is it reasonably possible to solder a bypass cap to adjacent pins on a ... opens, etc. ... I'm guessing that some skilled person could solder 0201 caps across ...
    (sci.electronics.design)
  • Re: Soldering bypass caps to QFP possible?
    ... Among other things I discovered a serious layout booboo. ... 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? ...
    (sci.electronics.design)
  • Re: Soldering bypass caps to QFP possible?
    ... John Larkin wrote: ... Among other things I discovered a serious layout booboo. ... 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? ...
    (sci.electronics.design)
  • Re: Soldering bypass caps to QFP possible?
    ... and that's also where the lone bypass cap dwelleth. ... the power pins. ... and drop down ground and vcc wires. ... it wouldn't be hard to solder wires to those pins. ...
    (sci.electronics.design)
  • Re: Soldering bypass caps to QFP possible?
    ... Among other things I discovered a serious layout booboo. ... 0.5mm pitch QFP chip or would that just open up a can of worms? ... those pins. ... although 01005 may be better in order for the solder to wick ...
    (sci.electronics.design)