Keith
I disagree strongly with your last sentence. I was there when it all
started. I can remember when electronics consisted of a wooden board or
box on which bakelite mounted component holders were mounted and the
interconnections were made by screwing solid wire under screw-and-nut
terminals. The great breakthrough came when I was very young and the
components were mounted on a metal chassis with solder tags, usually
direct point-to-point; where this was not possible, barettes of tags
were used to help out. This was the first use of solder in electronics.
At first, no special precautions were taken. It was only in the 1930s
that it took off, with the advent of cored wire. The PCB took off
commercially only in the 1950s and, as these were most frequently
hand-soldered, no change was made to the soldering technique. This was
entirely empirical and no reliability studies were made, up to this
time, so we had the confidence from 20 years experience in cored wire
solder. Wave soldering started in 1956 - and I witnessed the first
commercial prototype being put into service with initially disastrous
results: yes, I've known Rolf Strauss nearly 50 years. Initially,
exactly the same chemistry was used (halide-activated rosin). I also put
into service the first wave soldering machine in commercial service in
Switzerland and, two years later, converted it to water-soluble
chemistry (the company that employed me at that time are still using
water-soluble chemistry for hi-rel goods). The reliability questions
date only from the 1960s, so the confidence pre-dates the science. These
stem from the two problems of solderability and the effect of residues
(these had practically no effect with point-to-point wiring, other than
corrosion, which was mastered in the 1930s by limiting the weight of the
activators added to the rosin: there were standards to this effect).
Furthermore, I would say that the requirements of a solder joint
critical to keeping a 777 in the sky would be far different to those of
a Walkman. IMHO, we still have a long way to go before an avionics
assembly soldered with LF will have the same reliability as one soldered
with SnPb. In fact, I would hazard a guess that the most critical parts
will be soldered on ceramic-substrates as sub-assemblies within a decade
because of this mess, and it is a stupid mess generated by NGOs,
technocrats and politicians who know NOTHING except that lead is a dirty
word.
Brian
[log in to unmask] wrote:
> Dave,
>
> You are right that there is a difference between general and consumer
> electronics and "high performance" electronics. That does not mean, however, that
> experience gained in general and consumer electronics is totally irrelevant to
> high performance electronics. A solder joint does not "know" whether it is
> in a walkman or a jet fighter. All it "knows" is the mechanically and
> thermally induced stresses and strains to which it is subject and there can be some
> overlap in that range of "experience". In fact given the intrinsic weakness
> of tin-lead solder part of the design of joints for high performance
> electronics has been to try to ensure (e.g. by building in stress relief and reducing
> thermal mismatch) that the solder joints are not subject to stresses and strains
> that are too much more extreme than those experienced by a soldered joint in
> a walkman. The rapidly accumulating experience in consumer and general
> electronics can provide a foundation on which high performance electronics can
> build. As I have mentioned previously that is how confidence in tin-lead
> solder was developed.
>
> Keith Sweatman
> Nihon Superior Co., Ltd
>
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