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flux on PCB's after cleaning

jsk

#29590

flux on PCB's after cleaning | 21 July, 2004

problem: Too many solvents and boards are not clean

Flux remains on the board after vapor degreaser and "Powdery" white residue after vapor degreasing

Flux type is kester 186

Process: hand solder High Temp alloy, spot clean after hand solder

equipment: Vapor degreaser and spray wash batch cleaner

solvents used: proclean, Flux off-Rosin, BioACT EC-7R, vigon-A200, hydrochlorofluorcarbon (hcfc in vapor degreaser), Isopropyl alcohol

Possible problems that could be contributing to the situation are: Mixing the flux off chemical with proclean [using both (one after the other) to spot clean] QC stamp (white ink) from board house is smearing all over the pcb when you scrub with alcohol. Use bioact to clean the flux and then alcohol to clean the bioact.

After all this, it appears that brushing the board with alcohol and a kimwipe then loading in the degreaser yields the best results. The ole' wash the dishes before you load them in the dishwasher technique. I am not the process engineer nor am I the one who makes the decisions on what solvents to use but I am the one who has to deal with the problem as I am over the cleaning area. Changing to water soluable or no-clean is not an option. Why is this flux difficult to clean? Is anyone else using RMA flux having trouble getting thier boards clean if not what are you using to clean your PCB's?

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#29629

flux on PCB's after cleaning | 23 July, 2004

Consider your flux suppliers recommendations when determining the proper cleaning method for your boards.

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Steve Stach

#29634

flux on PCB's after cleaning | 23 July, 2004

Dear JSK,

It sounds like the root causes of your problem are two fold.

First, excessive heat will polymerize the abietic acid found in rosin forming neo-abietic diamers and polymers which are much less soluble than the parent monomer. There are several things you might try. To confirm this is what is happening, apply new RMA flux and reheat the area with the white powdery residue using moderate heat exposure (to boiling, not dry). Then, immediately clean the area and if the white residue is gone confirmation is gained. Corrective action here would be to (a) reduce the heat/time to make the solder connection, (b) add more RMA when making the connection to minimize polymer conversion, (c) hand clean the connection as soon as possible (while warm).

The second possible cause is the HCFC solvent. This is a poor solvent for removing ionic materials (activators) found in RMA fluxes. Hand cleaning can leave flux and activators behind if allowed to dry. Spot check for this problem by cleaning the area with hot DI water. If the ionic residue is removed, this is most likely your problem. Corrective action here is to change your cleaning process.

If you like to discuss further, please don't hesitate to contact the Austin American Technology team.

Steve Stach Austin American Technology (+1) 512-335-6400 ext. 20 sstach@aat-corp.com

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Sue PH

#29663

flux on PCB's after cleaning | 26 July, 2004

We use Kester 186 flux and the STU people would sometimes find white residue after cleaning with Isopropyl at the solder station. We have Lenium (Petroferm)in our vapor degreasers, and now they use Lenium at their stations as well as final clean, and we don't see that problem anymore.

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