If you look at the original Bellcore (now Telcordia) documents you find

that one of the worse things you can do for mixed technology PCBAs is to

use rosin based solder pastes for surface mount and then use water

soluble flux and aqueous clean for wave soldering.  Bellcore GR78 Core

has a set of procedures for determining if a rosin based flux is

"compliant" (i.e., compliant to their requirments).  Bellcore liked

compliant rosin based fluxes because they were not a reliability issue

if left behind.  In fact, reliability was usually improved by leaving

them behind in that they trapped ionic material so it wouldn't be mobile

and they also coated the PCB surface with an insulating rosin keeping

water off the traces. 





Regards, 

George 

George M. Wenger 

Senior Principle FMA / Reliability Engineer 

Wireless network Solutions 

Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531

[log in to unmask] 





-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden

Sent: Monday, April 09, 2007 9:08 AM

To: [log in to unmask]

Subject: [TN] Cleaning rosin flux with DI water..



Anyone have data as to what can happen if you remove (should actually

say ATTEMPT to remove) rosin flux residues with DI water?

 

Long story short, we buy a transformer that the mfr told me is soldered

with rosin, medium activity flux.  Their cleaning process is  "scrape

flux residues with a knife"....enough said about that...  We solder with

organic high activity and clean with DI water.  Guess what - return from

field with fire on the pcb...burned out a trace through the PCB under

the power pin of the transformer.  Since learning of the above info, I

am inclined to think maybe the rosin residue could have trapped water or

OR flux / flux residues and created a nice little corrosion spot.

 

Anyone have opinions or experience on what can happen if you try to

clean the "no clean" with just water?

 

 



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