Fabrizio Magistrali (Telettra at that time) wrote already 1990 in a 60 page paper about GaAs rel, that there is an increasing interest for more or less direct chip mounting, caused by higher encapsulation price (and some more reasons). This will require a much higher awareness and knowhow about environmental impact on semiconductors. Brian and David have given me some valuable inputs that way. Nearly all of our applications work well all over the planet, cross fingers, but the few that occur can still cost a lot of money. The few means many million dollars. So, we try to have a reasonable readiness for taking care of environment based failures, encouraged by such characters as per above.
(The electrical field is motor in some environment-driven activities, and the field is magnitudes higher in a modern semi chip, than on the board itself. E.g. even <5V chip will locally experience up to 5-50V/um. So, when something starts, it will accelerate faster than on the board. A consequence may be that the chips should also be magnitudes cleaner. Which I hope they are...)
/Ingemar Hernefjord
Ericsson Microwave Systems
> > >
> > >
> > > You have landed in a very nasty area. You are correct to be concerned
> > > about
> > > contamination issues.
> > > Even if the residues from the flux do not create migration/leakage
> > current
> > > problems they may
> > > collect other airborne contaminates that can cause problems.
> > >
> > > Process, shipping, and storage control are critical to the reliability
> > of
> > > the circuitry.
> > >
> > > If you wish I have a paper I presented in May of 2001 titled
> > > "Avionics Systems, Reliability, and Harsh Environments"
> > > that I could e-mail you. The information in the paper will
> > > give you a good idea of what type of airborne contamination
> > > issues you may have to deal with.
> > >
> > > David A. Douthit
> > > Manager
> > > LoCan LLC
> > >
> > > Bogert wrote: 6/20/2002 Folks is anyone manufacturing military PWAs
> > using
> > > no-clean flux and not cleaning the PWAs prior to shipment? If so, what
> > is
> > > your reliability experience with this process? We are considering a
> > > military application (Class 2) where mixed technology (SMT and PTH) PWAs
> > > will be soldered using no-clean flux and then not conformal coated
> > > (assuming the uncoated PWAs can pass our temperature/humidity
> > > qualification
> > > testing). Although the no-clean flux we will use should be benign (we
> > are
> > > having SIR testing performed to confirm this and Omegameter testing), I
> > am
> > > concerned that contamination may be introduced by other shop processes
> > > such
> > > as mechanical assembly, testing, etc., even if one uses gloves or
> > fingere
> > > cots during handling. One could argue that after shipment, since the
> > PWAs
> > > are not conformal coated, you can introduce contamination in the field
> > and
> > > therefore, why not not clean prior to shipment. We may be performing
> > board
> > > testing (boundry scan, bed-of-nails, etc) on PWAs that have been
> > soldered
> > > using no-clean flux. I understand that certain noclean flux can impede
> > > this testing, and also, may cause problems in event we need to conformal
> > > coat the PWAs. Any comments on this subject will be appreciated.
> > >
> > >
> > >
> > >
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