Are you convinced Pb-Sn are self healing at room temp after regular thermal cycle (4 season x some 50 years)? What's prediction if it is Leadfree ugly solder joint?
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----- Original Message -----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Sunday, May 08, 2011 06:47 AM
To: [log in to unmask] <[log in to unmask]>
Subject: [TN] Prehistoric solder joints
Sorting out some old junk, I came across the first object I ever made
with a transistor, dating back to 1955. In order to calibrate some
telecomms gear in the field, I needed something portable. I made a
couple of signal generators producing 0 dBm into 600 ohms at what was
then 1 kc/s (now 1 kHz). These were 100 x 64 x 25 mm, including a 4.5 V
"flat" battery. This was before PCBs (or even transistors) became
mainstream, so the wiring was component to component. The transistor was
a point-contact germanium type, made by a company in Newmarket, that
cost a fortune, at the time (£20, if I remember correctly, half a
graduate engineer's monthly salary!) and was so delicate that they
failed if you looked at them hard. They had to be soldered in at the end
of 30-50 mm leads with special short-circuiting heat sinks clipped to
the wires. Looking at it, I was astounded at the appearance of the
solder joints, somewhat corroded, but VERY ugly. Then I remembered the
100 W soldering irons we were using at the time, bare copper chisel bits
from about 8 mm diameter stock, filed into shape several times per day.
I thought it was a wonder I could solder anything so small with those
tools. Of course, thermostats were not even thought of in those days.
Temperature? Goodness knows, it was never measured, but I would
guestimate close to 400°C.
I know this device was used in several countries and my colleagues and I
used them for several years. The brass case of the survivor is bashed
and the paintwork reflects a hard life.
I thought to myself that it was undoubtedly buggered. I couldn't find
the right battery locally but asked my daughter to bring one out from
Switzerland at her next visit. I could see the switch was physically
broken, so I short-circuited it. I then reassembled it with the battery
and found that IT WORKED! I made up a load of a 560 ohm + a 39 ohm
resistors in series. Checking the output, it was amazing: 0.775 V RMS,
spot on 0 dBm at 995 kHz!!!! Not bad after 56 years! Maybe rotten, ugly,
uncontrolled, overheated, solder joints are not so unreliable as one
would imagine!
Brian
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