How do you place QFN32 parts?

funnynypd:
I used hot air removing parts before, curious can it be used for soldering? Anyone tried?

Greetings (No Name Supplied),

Sure! Its my prefered construction method for PCB prototypes.

I use an ordinary heatshrink gun after placing the parts

on solder paste hand applied from a syringe.

There no automation so the results are based on skill and

practice, much like soldering with an iron. The only learning

was to use such a small amount of paste (compared to

TH soldering with an iron).

Solder wick is a good tool for removing excess solder.

Hot air gives better results than a soldering iron as there is

no ‘tail’ caused when the hot iron is pulled off the solder

bump.

If the hot air is too strong or the gun held too close to the

PCB it is possible to ‘blow’ the parts off the pads or have

them tip up (aka “tombstoning”).

So far I’ve stuck to 1206 and SOIC footprints where possible

but also done well with TQFN32 packages.

Problem parts are those with large mass (in particular

inductors) and parts with little or no exposed pads (most

SMT electrolytics, trimmer caps). I have changed the

pad geometry for some of the parts I use often. Doing

these and any TH parts after hot air soldering and with

a hand iron works.

There is a risk of damaging the PCB if the hot air is

stationary for too long. The skillet method probably

gives more even heating.

Comments Welcome!