Terry- much of what you say is correct. But we have to look at some of the  

details.

1. The ionic cleanliness test was originally developed to determine if  

conformally coated military equipment would survive the  harsh temp/humidity 

conditions of S.E. Asia. In the words of the day, is the  floor clean enough so we 

can put down the wall-to-wall carpet? 

2. While most of the PWAs were assembled with RMA moderate to high solids  

rosin fluxes, many of the electronics makers wanted to use stronger fluxes to  

cope with the marginal component solderability of the era. Thus we soon had the 

 RA-Mil activity level fluxes to help with that issue.

3. The designs were generally through-hole, surface mount wasn't in common  

use until much later, esp. for mil use. Thus flux residue entrapment wasn't the 

 issue then that it became after the adoption of low clearance restricted  

cleaning agent flow SMT parts.

4. The Task Group work you have cited pointed out other concerns that  

weren't big issues with PTH/high solids fluxing agent designs; such as the  'dead 

band' in cleaning instrumentation response. 

5. All in all, these deeper investigations helped us all to understand some  

of the nuances of ionic cleanliness testing, which had taken on a standing 

that  was interpreted as an absolute guarantee of reliability, when it was really 

 developed as a process monitoring tool. Now in the test's favor, the level 

was  set to reflect ionic contamination levels based on clean and failed PWAs 

from  the field (U.S.Navy MRR-3-72), and confirmed by the lab work of W.  B. 

Wargotz at Bell Labs (see my previously offered SMT column  for the reference) 

so the pass/fail was not arbitrarily chosen.

6. To address your point about spot or localized high levels on  ionics, 

Wargotz has published on his work of making mini-cells on the PWA  surface by 

gluing a piece of Pyrex tubing to the surface using RTV, then putting  in a 

controlled volume of test solution, a micro conductivity or  resistivity cell to 

obtain spot readings in known entrapment areas.  Hopefully, such work would 

result in design changes so the overall average ionic  contamination level would be 

indicative of good field performance. (This paper  may have given at one of 

the IPC World Conferences, I'll have to check my files  to see if I still have 

a copy).

7. Terry- thanks for bringing your points up, so they can be discussed in a  

way that helps members of the TN community better understand ionics and 

testing.   



Bill  Kenyon

Global Centre Consulting

3336 Birmingham Drive

Fort Collins, CO  80526

Tel: 970.207.9586   Cell:  970.980.6373









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