Ramon,
The answer is YES!!!
Go to http://residues.com as a starting point.
Virtually all the labs can give you wonderful stories about
contamination induced failures.
David A. Douthit
Manager
LoCan LLC
================================
"Dehoyos, Ramon" wrote:
> Brian:
> My appologies for stretching this subject since I know very little
> beyond empirical experience. I was talking about different types of boards
> including boards that performed in the giga frequency. At one time we were
> producing about 20K boards per month and several thousands were of the high
> frequency application type.
> Are there any reports or articles that indicate field failures
> from boards not being properly cleaned?
> Beat Regards,
> Ramon
>
> > -----Original Message-----
> > From: Brian Ellis [SMTP:[log in to unmask]]
> > Sent: Monday, September 08, 2003 10:19 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Ionograph
> >
> > It can depend on the application. Obviously, high-impedance, high
> > frequency applications, used as portable equipment with a high
> > reliability required, cannot be considered in the same breath as the PC
> > driving the screen you use to read this.
> >
> > However, be aware that salt is not usually the problem but solder flux
> > residues and general handling contamination. This is why the correct way
> > of expressing the unit is n µg/cm2 eq. NaCl, the "eq." meaning the
> > electrical equivalent, not that there is actually NaCl present.
> >
> > Brian
> >
> > Dehoyos, Ramon wrote:
> > > Brian:
> > > Besides biomedical electronics in which boards need to be
> > > super clean, it has been my experience that any thing under 10 micro
> > grams
> > > of NaCl per square inch is passable. So far I have not heard of a case,
> > > while tallking to my co-workers in several companies, where there has
> > been
> > > any problems releted to salt contamination. Could you expand on this
> > matter.
> > > Regards,
> > > Ramon
> > >
> > >
> > >>-----Original Message-----
> > >>From: Brian Ellis [SMTP:[log in to unmask]]
> > >>Sent: Saturday, September 06, 2003 3:29 AM
> > >>To: [log in to unmask]
> > >>Subject: Re: [TN] Ionograph
> > >>
> > >>IMHO, to say 1.56 ug/cm2 eq NaCl or any other figure is useless without
> > >>qualification. Would it be reasonable to use this figure on both a
> > >>through-hole circuit with conductor spacings of 0.5 mm and no
> > >>significant traps under components and a high density interconnect
> > >>structure with shadowing components and gaps under them equal to the
> > >>copper thickness? Of course not, it is ridiculous. The figure quoted was
> > >>derived from conditions in the first case, in the 1970s, before SMDs
> > >>were current. IMHO, the figure, for equal reliability, must be
> > >>proportional to the maximum voltage gradient. In the first case, we are
> > >>talking of e.g. DILs working at 5 V, so we have a voltage gradient of 10
> > >>V/mm. I agree my example is perhaps extreme, so let's say 50 V/mm, for
> > >>the sake of a more practical argument. Your HDIS may be using
> > >>semiconductors working at 3.0 V with minimum track/pad spacings of 25
> > >>µm, ie a voltage gradient of 120 V/mm (roughly the maximum advisable
> > >>with FR-4, before dissociation starts), so if 50 V/mm and 1.56 µg/cm2
> > >>are OK, then you would want 1.56 * 50/120 = 0.65 µg/cm2, assuming equal
> > >>accessibility of cleaning fluids under the components. As this is not
> > >>the case, I suggest we have to weight the figure to compensate. I
> > >>propose a factor of 3 (from experience, we know that a tight SMA is 3
> > >>times more difficult to clean to an identical level than a 1970s style
> > >>assembly). It would therefore seem that 0.2 to 0.25 µg/cm2 eq. NaCl
> > >>would seem the most judicious figure to get an identical level of
> > >>reliability, all other things being equal. Empirically, this argument
> > >>would extend to ~0.5 µg/cm2 eq. NaCl for a tightish non-HDIS SMA.
> > >>
> > >>That having been said, these arguments apply only to cases before
> > >>conformal coating is applied (MIL-P-28809n is specific on this point) to
> > >>avoid vesication and to apply the same arguments to circuits without
> > >>coating is totally unreasonable, because the conditions of operation are
> > >>totally different. Specifications have never considered this and are
> > >>therefore useless. IMHO, the only thing to do is to determine your
> > >>figure empirically. Unfortunately, this cannot be done overnight and
> > >>requires great knowledge of how your products are going to be used and
> > >>under what climatic conditions. You can try accelerated tests but they
> > >>are difficult, even impossible, to correlate with real-life conditions,
> > >>but they may give you a starting point. If products coming back for
> > >>subsequent repair show any signs of environmental damage, then you have
> > >>to tighten the figure. If they come back in a pristine condition or
> > >>don't come back at all, then you may be able to relax your figure
> > >>slightly.
> > >>
> > >>Again, IMHO, no one here can advise you, without knowing a lot more
> > >>about your products, the required reliability over a length of time and
> > >>the conditions of assembly, cleaning and use with a specific figure. It
> > >>may be that your 20 µg/cm2 is OK for you (although I very much doubt it,
> > >>as this figure is outside my knowledge of acceptable figures - and I am
> > >>one of the pioneers of ionic contamination testing, having worked for
> > >>over three decades on this and related subjects).
> > >>
> > >>Please do not assume any figure is correct for you, without
> > verification.
> > >>
> > >>Brian
> > >>
> > >>Angela Gregor wrote:
> > >>
> > >>>First I wanted to thank you all for the gasket information you gave.
> > >>>Evidently this forum is very much respected because I didn't get any
> > >>>arguments from anyone here. Here's another one. At our company we are
> > >>>currently using Ionograph 500m version 3.02 to test our assembled
> > boards
> > >>>after wash. Our pass/fail limit is 20 micro grams of sodium per square
> > >>>centimeters. I'm not sure our calculation is correct, and I was
> > >>
> > >>wondering
> > >>
> > >>>what other companies pass/fail limits are for comparisons. I called
> > >>
> > >>about
> > >>
> > >>>three places in my area and got three different answers. If this helps
> > >>
> > >>most
> > >>
> > >>>of our boards are double sided. I would appreciate any feed-back.
> > Thanks
> > >>
> > >>in
> > >>
> > >>>advance.
> > >>>
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