[TenTec] Omni VI - soldered joints. Caution.

[Ken Brown]

Hi Mike,

Properly made solder joints should not deteriorate enough to cause a 
failure in your lifetime, except perhaps in a corrosive environment. If 
the soldering was not done properly in the first place failures may 
occur. Anything that causes the current density through the solder to be 
excessivly high, or the resistance through the solder joint to be high, 
could cause the solder to partially melt from the I squared R heat 
produced. If the solder melts and flows in such a way that an even 
smaller cross section of solder is carrying the same amount of current, 
then the heating and melting will get worse, and the joint could 
eventually fail. These kind of current density problems are probably 
more likely in higher power RF circuitry. "Skin effect" makes the 
current not evenly distributed through the solder. Insufficient solder 
applied, or incomplete cleaning of the surfaces of the printed circuit 
board or the components are all possible beginnings of this problem. A 
design that does not use sufficiently sized solder pads on the printed 
circuit board could be asking for trouble too. If the PCB has a solder 
resistant coating between traces, and the silk screening process for 
applying this coating was out of registration, less than the whole 
solder pad area could be in use.

DE N6KB