Vectronics VEC-1500K - Manual (Page 36)

31
Not Enough Just Right Too Much
Common PC Board Problems: The three most frequent problems occurring
with soldered connections are:
Cold Solder Joints: The "cold solder joint" is a catch-all term for connections
that fail to make a reliable electrical contact. This could be due to one of the
following:
1. A "grainy" or fractured joint formed because it was disturbed during the
plastic phase of cooling.
2. One solderable surface on the connection was heated insufficiently, and
bonding failed.
3. Retraction due to oxidation caused the joint to fail due to insufficient contact
area.
Cold solder joints can often be repaired by re-heating and re-activating the joint
surfaces with the introduction of more flux and some fresh solder.
Solder Bridges: These short circuits are usually the result of "gapping" between
two adjacent pads or tracks (60/40 solder is more likely to gap than 63/37).
Usually, removing some of the solder with wick or a solder vac will eliminate the
problem.
Lifted Pads: A pad lifts when its bonding to the PC board fails due to excessive
heat. A lifted pad, by itself, may not cause an immediate malfunction. However,
sooner or later, a track break usually occurs at the junction of the lifted pad and
the still-secured pc track. The fastest repair technique is to install a new part,
and then solder the unclipped lead to a point further down the incoming track.
Cold-Solder Joint
Solder Bridge
Lifted Pad
Looking for trouble (or excellence) in a solder connection is a little like going on
an archeological expedition! The story is virtually always there, recorded for the
ages in the solder itself. All you need do is look closely and read the signs!