Just pretest the troublesome parts, to avoid raising the labor cost aspect too high, that way a cost savings gain is accomplished, via the reduced cost of rework.
Just about anything can be tested well, if time and common sense is taken to look at what the device is supposed to do, and what happens during failure modes, just take your time. A lot of this is comes down to pure, basic, simple physics, such as the case about avoiding thermally shocking a tantalum caps (see other replies to this subject). Materials need time to expand evenly thus semi-slowly, making air heating ideal, or a momentary temperature gradient will form at the surface and outer layers, while the core remains momentarily cold, with this condition, internal fractures become a real possibility (try dropping an ice cube into tepid water). The effect is especially pronounced where dissimilar materials with significantly different coefficients of thermal expansion are bonded to each other. That is why, and I am inclined to go with the rules of physics, and the advise of the experts that build the components (they know what's in there), and also the feedback of those who try to put them to use, as to what type of test to perform, and what number to aim for. This is much more rational, rather using than a generic IPC or other standard, since rarely, can all situations be shoehorned into a catch all, generic standard, and cover all bases, needed!
Ronald J. Leckfor
BSAS-Electrical Engineering Technology
Youngstown State University, 1997
REM Electronics Supply
Value Added Division
Warren, Ohio
330 373 1300 X 240
-----Original Message-----
From: Raymond Klein [SMTP:[log in to unmask]]
Sent: Friday, June 04, 1999 1:15 PM
To: [log in to unmask]
Subject: Re: [TN] Tantalum caps and the big bang
Ron,
Nailed!!! Once again my quick-and-dirty approach is exposed for what it is!
You're right, hand-held multimeter will show a continuous current rather
than an exponentially dropping one. With an appropriate series resistor
capacitor heating is eliminated. I'm just an engineer (not a QA type). Are
there standard incoming inspection tests for cap's? The problem of
mis-labeled tant caps is not at all rare. I know that most of my assemblers
do not test incoming parts. Perhaps they should. Is there a IPC or other
standard I can refer them to?
Ray
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
