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N_Cook

On 16/12/2016 19:11, wrote:
On Friday, December 16, 2016 at 12:07:12 PM UTC-5, N_Cook wrote:
Third time in as many months, usual PbF phantom problems, solder looks
fine but no wetting between eyelet and pin and grey (tinpest?) pin, even
after desoldring.

I will render an opinion here based on my experiences with conventional lead-containing solder of differing natures.

a) Non-Eutectic solders will solidify in a non-linear fashion as it cools.
b) My experience with 60/40 and 50/50 solders with wires is that the cooling is often based on the wire as it is a heat-sink.
c) Dynaco equipment uses a lot of eyelets set in circuit boards.
d) Using solders as described above, on more than one occasion I have gotten visually excellent connections that simply twirl in the eyelet, as the solder cooled (dumped heat into the wire) so fast that the shrinkage pulled it away from the eyelet before it was actually solid.

This is purely anecdotal.

Today, I use only truly eutectic solders on my electronics (37/63 lead/tin) - with a very few exceptions, when for one reason or another I need to use silver bearing solder. In those cases, I use 96/4 tin/silver, and great care not to move anything as it cools.

Peter Wieck
Melrose Park, PA

I suppose part of the problem, the pins are square cross-section , not
round. Then localised stressing edges for tinpest to develop.
Remedial action will start by grinding back to an axial surface on all
such pot pins, on the solder side of the pcb before resoldering. Then
what other components will be eyeleted as well will need such attention,
the main electros yes, minor electros will they be eyeleted , 1W and
above Rs also, difficult to visually tell. I suppose the rule is
anything big is likely to be eyeleted, plus any component resource with
smaller pins.