Hi Steve:
- At the risk of being irresponsible for offering advice when nature of the
pwb (single sided, double sided, multilayer, laminate type, etc.), product
environment (vibration, mechanical shock, thermal excursions [number/rate])
and lead material are unknown, the following come to mind (this is called
shooting from the hip).
- 1) Get the pwb fixed at the fab house to eliminate the problem, or
- 2) If the pwb is single sided, double sided or multilayer and the diodes DO
NOT connect to an internal layer, then go get a drill and relieve the holes to
accommodate the diameter of the lead. Presuming the leads are Kovar, Alloy 42
or something similar, mount the diodes vertically with a straight through
(stud) termination and solder from the bottom (solder side) of the pwb. If
the diode leads are something other than Kovar, Alloy 42 (e.g. can be formed)
then mount the diode as above, but use a partial or full clinch of the leads
and solder. In either case above you might want to use a spacer to keep the
body/coating meniscus out of the hole and thereby assure the maximum possible
wetting of the solder to the lead. Depending on the mass and aspect ratio
(location of CG above pwb surface) you may need to additionally stabilize the
diodes with an appropriate adhesive if shock or vibration will be seen in
field service.
- 3) If the pwb is multilayer and the diodes need to make connection to the
inner layers your best hope (real estate available) is to mount the diode
laying down on the pwb as follows: a) Solder bifurcated terminals into the
offending holes. Orient the terminal forks so that the diode leads can be
laid into the forks and soldered. Secure the diode to the pwb surface with an
appropriate adhesive for mechanical reinforcement. (Note, this method
engenders a minor reliability risk to the integrity of the pth if thermal
cycling will be a fact of field use.) or, b) Form bus wire into question-mark-
shaped jumpers, using appropriate adhesive, mount the diode laying down on
the pwb surface and (after the adhesive sets) put the hook of the question
mark over the diode leads with tail of the question mark in, and extending
well through, the pth. Use a full clinch of the bus wire on the bottom
(solder) side of the pwb. This method is slower, will be more labor-
intensive, but will not pose a risk of pth damage and the attendant
reliability impact.
Hope this helps some, I'll reholster now ;-). Jim Moffitt, Moffitt
Enterprises Consulting
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