How to hand-solder a Micrel module (don’t)


I’ve been developing a RF transceiver for use with my Kadet.  I really like these Micrel RadioWire modules, but they basically must be reflow soldered.  They’re also about $16/ea. in single unit quantities, so I want to make sure that the carrier PCB works before I solder on the module (I’ve made that mistake already!).  With that in mind, I had to figure out how to solder the module on after all the other components were installed.  This means hand soldering.  Looking on the datasheet, they say that it can be done, using solder paste.  So, here’s documentation of my attempt.

PCB ready for module

PCB ready for module

This is the starting point.  I cleaned the surface with isopropyl alcohol (IPA).

Solder paste applied

Solder paste applied

I applied the solder paste as normal, and cleaned the module with IPA as well.

Module seated, waiting for heating

Module seated, waiting for heating

This is just before heating the pads with a soldering iron.  I heated each one until the solder melted, but it didn’t bond with the module.  Before I got too far, I removed the module and examined the results.

Results of the first attempt

Results of the first attempt

I cleaned all the surfaces with solder wick and IPA, and tried again.

Results of attempt two

Results of attempt two

This time, I held the soldering iron on each pad for much longer.  The solder bonded to the module and the PCB, and it held tight.  However, I took a multimeter to it, checking for continuity.  Nearly every pad was shorted with it’s neighbor.  This sucks.

Another view of try two

Another view of try two

With the module throughly bonded with the PCB, and no way to remove it and try again, I decided to try the hail-mary.  I figured that at this point, unless I could think of something, the whole thing was ruined.  With that in mind, I decided to try to reflow the whole thing.  I really had no idea if it was going to screw everything up, especially the FTDI chip on the bottom of the board.

During reflow

During reflow

The reflow went well, I’m pleased with the look of everything.  I also confirmed that the pins are electrically isolated.  Also, on first glance, everything seems to work.  The microcontroller and USB-to-serial chip still work.  I really just need to verify that the transceiver module works, and it will be a complete success.

The moral of the story is:  Don’t attempt to hand-solder the Micrel module.  It probably won’t work.  On the other hand, if you do get it to work, drop me a line, I’d like to know how.

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