Hi:

I built the M3 Semiconductor Analyzer from a kit.  But it failed to pass the 
short circuit calibration.  [PIC]  Uses 16F876 and three 4052 analog switches 
in a very cleaver circuit that recognizes many 3 terminal devices and measures 
key parameters.  http://www.prc68.com/I/MTE.shtml#Xistor

Radio Shack no longer carries flux remover.  But why would flux bother a short 
circuit calibration.  But after getting some alcohol and cleaning the board it 
passed the calibration.  The other problem is that the copper is extra thick 
and my SMT sized soldering iron was not able to heat the joints.  I saw the 
dull color and thought it must be a RoHs lead free PCB.

The M3 SA can connect any device pin to either +5 V or to ground and insert a 
resistor of 100, 1k, 10k or 100k in series with each device pin.  The device 
always has at least a resistor to ground and another resistor to +5.  So 
measuring the voltage at all the device pins allows the computation of both the 
voltages across the device and the current through each pin.  The voltages for 
the currents are small and a flux path to +5 or ground is very disruptive.

Working with solder wick on SMT parts I learned THE major reason for using 
flux.  It's not to  clean the joint, but rather to provide a good thermal path 
to heat the joint.  Prior to using a flux pen to wet the solder wick my results 
were spotty.  But when using flux to wet the wick it works great each and every 
time.

In a similar manner applying a very small amount of flux bridging the parts to 
be soldered gets the heat to them, which is not easy to do with a dry iron on 
dry parts.  Flux pens come in different flavors so you can get one with the 
type of flux you like.  Highly recommended.  Get 2 or 3 since shipping them is 
a hassle.

-- 
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com

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