Steve, it sounds like you will try to do an ambitious designed 
experiment.  Are you acquainted with experimental design techniques, or 
do you have access to someone with such experience?  A few weeks ago I 
did a small designed experiment to test methods or cleaning unpopulated 
circuit boards.

Here are my comments on your questions.

1.  Significant differences, if any, should show up in the statistical 
analysis of your designed experiment  data.

2.  I used an Alphametals Omegameter 600R.  An isopropyl alcohol solution 
flows around the board and the resistivity of the solution monitored.  
People tell me a heated alcohol ionograph is better.

3.  Gauge R & R (repeatability and reproducibility) is a good question.  
Even if you could put a known amount of contaminant on a board, in 
measuring it you would destroy (clean) the sample.  For our Omegameter, I 
would think of doing a so-called "chemical verification" of its 
performance by adding a fixed quanitity of standard salt solution 
multiple times and using the data for R & R analysis.  Of course, that 
would not be the same thing as using real PC boards.

For your information, one piece of information that came out of the 
experiment here was that there were big differences in cleanliness or 
ability to be cleaned between dry film solder resist and liquid 
photoimageable solder resist.

Contact me if you want more information.

Lou Hart 412-858-6117


.

On Sun, 2 Jun 1996, Steve Mikell wrote:

> We are reviewing our alternative cleaning process for application of SPC
> methodologies.  The first system to be subjected to the microscope will be
> an in-line water cleaner using a water miscible solvent in the wash.  During
> the course of our evaluation we will attempt to determine the variation in
> the temperature, spray pressure, bath concentration, bath loading, belt
> speed, and incoming water quality.  We also intend to attempt to determine
> the impact of the variation of each process element as well as determine any
> significant interactions.  We have the following questions for comment:
> 
> 1.  What would be considered a significant variation in the cleanliness level?
>      a.  What variation should I see board to board of the same part number
> coming off the same process?
>      b.  What variation should I see board to board of different part
> numbers, but using similiar parameters in the soldering process ?
>      c.  Has anybody studied their flux and soldering parameters to
> determine when they see large increases in residues due to adverse affects
> on the cleanibility of the flux caused by excessive heat and dwell ???
> 
> 2.  What test methodologies would be best used to determine cleanliness
> level for this effort?
> 
> 3.   Has anyone done a gage R & R on their test methods?
> 
> I would also appreciate hearing from anyone who has conducted such a study,
> with information on the engineered limits you established.
> 
> Your responses are appreciated
> Steve Mikell
> SCI Systems, Huntsville, ALA
> [log in to unmask]
> Steve Mikell, Process Engineer, Soldering & cleaning processes
> SCI Systems Plant 13
> [log in to unmask]
>