Jeff Liebermann wrote in message
...
On Thu, 08 Dec 2011 18:37:06 -0500, Boris Mohar
wrote:

Took apart a Volvo 850 fuel pump relay. Cracks everywhere.
http://www.viatrack.ca/Misc/FP%20Relay/

What year Volvo? The Volvo 850 was made from 1992 to 1997. This was
somewhat before RoHS solder was introduced en masse. Looking at the
photos and guessing by the age, methinks it's just a typical lead-tin
cracked solder joint produced by excessive vibration. It's not that
unusual for fuel pumps:
http://www.volvoclub.org.uk/faq/EngineFuelinjection.html
Scroll down to "Testing or Repairing Bad Fuel Injection Relay".
Also:
http://www.tegger.com/hondafaq/mainrelayoperation/badmainrelay.html
and others. Note the relay boards which look much like your photos.

In a past life, I used to design marine radios. We had solder
cracking problems on unsupported heavy parts (xformers, power
resistors, big electrolytics, etc) due to engine vibration and shock.
Oddly, the solution was NOT to support the part, because the load was
too great and would crack the glue. It was to decrease the size of
the PCB hole down to a tight fit. That would cause the vibrational
loads to be transferred to the PCB and therefore reduce the stresses
on the solder joint. With a large hole and fairly soft solder, the
solder tends to get extruded out of the hole eventually forming a
annual ring around the lead. (Hint: copper leads are harder and
stiffer than solder).

Somewhat later, we started using rubber washers and preforms under the
heavy components to help absorb the load. Imported electronics often
uses yellow acrylic goo to support top heavy parts, but makes rework
and quality control a PITA.

If you want to see how such a joint is formed, shove a heavy copper
component pin into a loose PCB hole and solder the pad. Find a
vibratory scraper or ultrasonic scaler that will accept a chuck. If
you have time, a vibrating toothbrush will do it after a few hours.
Connect the chuck or clamp to the wire lead. Vibrate until the lead
comes loose. You'll find that the crack somewhat resembles the
annular ring crack.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS


PCB holes somewhat larger than the component pins always, given time, would
cause ring cracks in solder but with PbF occurs in just a year or two. For
things like pcb mounted multi-terminal transformers they could have an extra
machining stage. A conical grinding or milling stage, per hole, on the side
that accepts the component so that larger holes could be avoided and still
not mess-up the hand alignment/placement due to microscopic , but in spec,
misalignment of the pins