[Elecraft] (OT) Baking PC boards in the toaster oven...

[Larry Phipps]

All that is undoubtedly true... but if you still want to try it, I would 
think you would get better results with a convection kind of toaster oven.

Larry N8LP



Henry Gardiner wrote:

>   SMT soldering was designed to obtain high volume and high quality 
> solder joints with great uniformity so that detailed inspection and 
> rework are not necessary.  It does this at considerable investment 
> expense up front.
>   The paste solder must be applied in a precise amount.  This means a 
> stencil printer (most use optical alignment) and multi-hundred dollar 
> stencils, or a robot that applies dabs in precisely metered amounts.  
> Hand application will not work adequately.  Smear the solder on those 
> narrow smt ics even slightly and a solder short results.  Not enough 
> solder, and the lead won't wet.  Too much, and the joints short or are 
> hard to inspect.  You end up with the extra step of inspecting every 
> joint (which is not done often in the industry) and doing a lot of 
> touch-up by hand.
>   Then the component must be placed precisely on the pads of solder 
> without lateral motion that would smear the solder and cause solder 
> joint problems.  In industry, robots do this at high speed and 
> precision using software that determines from coordinates and optics 
> where to put each component.  Just about impossible to do by hand 
> unaided at any speed.  But a person could rig up some very slow manual 
> pick and place device.
>   Circuit boards that have been sitting around for months start to 
> lose their wettability.  This adversely affects the uniformity of the 
> solder joints.  The high volume of a factory provides considerable 
> protection against this problem.
>   Most smt ovens heat the air and blow the air around the boards at 
> high volume.  Compared to radiant heating this provides much better 
> regulation of component temperature-time profiles despite differences 
> in component colors and geometries, and the biggest factor, the 
> thermal mass of the circuit board itself.  The circuit board forms 
> half the joint.
>   To obtain the temperature vs time profile needed, most factory smt 
> ovens are actually a chain of several ovens connected together 
> linearly over a moving belt.  Each oven operates stabilized and 
> uniform at a different point in the temperature profile.
>   Unless you want to buy good equipment, you will be inspecting every 
> joint, doing a lot of touch up and replacing fried components.  You'll 
> have a lot of field failures from intermittent joints.  Toaster ovens 
> don't make sense.  Single cavity ovens could be made to work well if 
> there's a lot of moving air and if the walls of the oven and the air 
> can be kept very close to the temperature profile, including the 
> cool-down phase.
>   For experimenters, it makes much more sense to stick with the larger 
> smt sizes and solder them in by hand with a soldering iron and 
> hand-held solder.
>
> Henry AC5LA
>
>
>  
>
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