Our final rinse is fed from a recycling unit that produces DI water. We use
.5 mohm-cm resistivity as the low limit. With fresh resin beds we get 17.5
mohm-cm water into the final rinse and then it goes downhill from there.
When we hit .5 we change the beds. The .5 limit was based on input from the
recycling unit vendor and what their customers typically use. This is how he
broke it down:

The semiconductor industry needs 17 mohm-cm.
High purity for high reliability (military, life-support) boards would be 1
mohm-cm.
High purity for commercial boards would be .5 mohm-cm. He considered .5 to
still be DI.

Of course, you need to look at your application and determine what will be
acceptable for it. I think there was a recent thread on TechNet regarding
using conductivity vs. resistivity as a measurement of water quality. You
may want to search that out and read it. Since the meter on our equipment
measures resistivity, that is what we use.

Bob


Robert Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020 x3035
Fax: 856-234-6679
email: [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Alain Savard
Sent: Tuesday, June 05, 2001 11:44 AM
To: [log in to unmask]
Subject: [TN] Minimum requirements for final rinse in assembled boards


Hi netters,

A question from a colleague of mine. Subject: Water soluble flux rinse
water.

What is the minimum water cleanliness level of the final rinse for
assembled/soldered PCB?

Reference?

Thanks a lot,


Alain Savard
CAE Inc.

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