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February 1998

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Subject:
From:
Karen Tellefsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 17 Feb 1998 16:16:58 -0500
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> From: Kathy Palumbo <[log in to unmask]>
> To: [log in to unmask]
> Subject: [TN] Cleanliness Test
> Date: Tuesday, February 17, 1998 2:32 PM
> 
> I have been performing a cleanliness test on some product.  The method I
> used was as follows:
> 
> Mixed a solution of 25% DI water with 75% alcohol.

Do you check this by specific gravity?

> 
> Calibrated the Conductivity meter using a saline solution with a known
> conductivity level.

What is your conductivity solution?  How does it compare to low 
concentrations of NaCl in 75% IPA/25% H2O?
It might be a good idea to measure small concentrations of NaCl
in 75% IPA/25% H2O by your method. 

> 
> Measured the level of conductivity of the solution.

At what temperature?  Do you purify it with an ion-exchange column?
> 
> Soaked the test specimen for 15 minutes.

Solution temperature during soak? Aggitation, if any?
15 minutes at room temperature with no aggitation 
may not remove enough of the ionic soil on the board
to ensure a good cleanliness test.  If you don't, I'd suggest 
you aggitate, heat or both.  A starting point may be Phil 
Whittmer's "modified ROSE," which uses a non-
aggitated soak at 75°C in  75% IPA/25% H2O
for an hour with good results.

Aside:  For Ionographs, I recommend at least 15 minutes 
at 45°C (depending on the size of the board) for ionic 
contamination measurements.  Ionographs necessarily
aggitate.
> 
> Removed the test specimen from the solution.
> 
> Remeasured the level of conductivity of the solution.

At the same temperature as the intitial measurement?
> 
> My question is this:  Should this be a go, no go test?  If I measure any
> additional conductivity do I have a level of ionic contaminant which
> will cause issue later (we use a water soluable paste)?
> I measured .2uS/cm to .25uS/cm more than the initial reading.  Is this
> cause to be concern? 

It depends.  How big is your board?  What sort of components are on it?
What volume of solution do you use? What are the answers to my previous
questions?

> Should I send the boards out to a lab and have a
> more accurrate cleanliness test done (we build to Class II
> requirements)?
> 
If done with proper care and understanding of what you are doing,
this sort of test is as good as any Omegameter or Ionograph testing.  
It can be sufficiently good for a process control measure of your cleaning.
Now the marketing guys will kill me.  However, if you aren't doing this 
right, this test won't give you useful information, and you are better off 
with automated ionic contamination tester or sending your boards out
for testing, where there is much less possibility to mess up. 

> Thanks in advance for your input!
> 
> Kathy Palumbo
> Mfg. Engr.
> Viking Components
> 
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