[Elecraft] Resistor and capacitor installation techniques: trim before or after soldering?

[Don Wilhelm]

Actually one of the important points in soldering with thru-hole 
components with plated hole boards is to watch the solder flow as you 
solder.  You should see the solder wick down into the hole which 
minimizes the chances that the lead trimming process will cause a 'shock 
wave' that will fracture the solder.

Put the soldering iron in contact with both the component lead and the 
solder pad (and keep it there).  Apply the solder to the joint on the 
opposite side from the iron (a very small bit of solder at the iron tip 
will aid heat transfer).  Then watch the solder flow.  It should flow 
out to an almost invisible edge on both the component lead and the 
solder pad, then keep the heat on just a bit longer and the solder will 
wick down into the thru-plated hold.

The entire process should take at least 2 seconds, but likely 3 seconds. 
  With heavy leads on components, it can take up to 5 seconds.

One thing that can help with fractured solder is the use of 'eutectic' 
solder alloys - the 63/37 alloy is one of them.  Those have no plastic 
state - they go directly from molten to solid, and there is little 
danger of a "cold solder joint" if anything moves during the plastic 
state.  The more commonly available 60/40 alloy does not have that 
property, and must not be moved while the solder is cooling.

73,
Don W3FPR

On 3/24/2018 6:51 PM, Howie WA3MCK wrote:
> When I went to “mil spec soldering school” at Sanders Associates in Nashua
> NH back in the 80’s we were taught to install the component and
> mechanically secure it BEFORE soldering. This included clipping the leads
> of resistors, capacitors, and so forth.
> Why?
> When you clip a component lead it creates a very small “shock wave” that
> passes through the lead and on to the component. In some rare cases this
> MIGHT weaken the solder joint.
> Our boards were even weighed before and after assembly to estimate the
> total amount of solder applied.
> ALL joints were inspected under a stereoscope.
>   All of this (and more) was part of the quality control and assurance
> program.
> This helped to reduce MTBF (mean time before failure) for our circuit
> boards.
> In my case I installed BRD-6/7 RDF surveillance receivers on Nuclear Attack
> Boats.
> Failure was not tolerated.