Subject: Re: [TN] HELP! Conformally coating  on no clean flux pcb

     Mike,



     I was going to ask a similar question.  We have a situation where an

     assembly house that we are looking at only has a no-clean process and

     we then need these PCB's conformally coated.  The same question came

     up about adhesion and reliability.  What I have found out  is that

     people have done test but you can't make any generalizations when it

     comes to these tests.  Different flux chemistries may or may not work

     with different coatings.  Another side of this issue is how clean are

     your raw circuit boards when they come in from your board house?  Do

     your people use rubber gloves while handling the PCB's? I doubt it.

     Human finger grease, dirt, etc, in my opinion, is worse than any flux

     residue.

     So you have to worry about that plus the flux compatibility. Give me a

     call if you want to discuss this further...



     Mark Pozorski

     Sr. Mfg. Eng.

     ADC Telecom.

     612-936-8395









______________________________ Reply Separator _________________________________

Subject: [TN] HELP! Conformally coating  on no clean flux pcb

Author:  "TechNet E-Mail Forum." <[log in to unmask]>           Mike Waters

<[log in to unmask]> at Internet-Mail

Date:    8/3/98 7:12 AM





TechNet,

I need advice badly.  In our wave solder process we use no clean flux.

We have an application where the assembled pcb has to be conformally

coated to withstand up to 100% condensing humidity and 95% non

condensing humidity in ambient temp ranges from -20deg C to +85 deg. C.

A concern has come up with the long term reliability of the conformal

coating based on cleanliness of the pcb prior to spraying the silicone

or polyureathene coating (from previous posts, I am assuming silicone

will be the best of the two solutions).  It has been suggested that we

water wash the pcb after solder before application of the coatings.  The

board is double sided with larger magnetics on the component side and

includes SMT.  In your experience, has anyone had problems using no

clean flux in conjunction with silicone coatings with respect to field

reliability?



Regards,



Mike Waters

Phone:  919-767-3815

Fax:    919-767-3966



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