Charles

I'll try and answer some of your questions

I've not seen this particular problem on heat sinks before but on lots of other
engineering hardware. The quality of finish achieved can be very variable
depending on the quality controls used by the processor. If done properly a good
finish will withstand 168 hrs salt fog test. However, Alodine is a chromate
conversion coating which will be bleached and eventually removed by an alkaline
solution, also temperatures above 60 centigrade will degrade it.


As to overcoming the problem try solvent cleaning or if this isn't feasible look
for a cleaner with a neutral pH chemistry. Couple this with a better quality
Alodine finish and you should get a serviceable product.

Regards

Chris Evans
Matra BAe Dynamics
England




______________________________ Reply Separator _________________________________
Subject: [TN] Fwd:Alodine washing off
Author:  "TechNet E-Mail Forum." <[log in to unmask]>, [log in to unmask] at
INTERNET
Date:    04/09/98 19:51


*** TFS Evaluation Copy of module : cc:Mail ***


____________________Forward Header_____________________
Subject:    Alodine washing off
Author: CharlesC
Date:       9/3/98 6:02 PM

We are having a problem on a PCB which has an Aluminum stiffener/ heat sink
bonded on the component side=2E When we recieve the board the Alodine is quite
dark but after aqueous cleaning the finish lightens enevenly and after three or
four washings we have what appears to be bare aluminum=2E The board manufaturer
tells us that indeed the finsh has come off=2E This is only happening on one
part
number PCB, the other board from the same manufacturer does not exhibit the
problem=2E We do try to minimize washings but due to the nature of the assy=2E
fo=
ur
washings is about as low as we can go=2E We use an inline aqueous cleaner our
saponifier contains monoethanolamine, the water is R=2EO=2E and the temperature
i=
s
160deg=2EF

I have the following questions:
1=2E Has anyone else had this happen=2E?
2=2E Does a high PH remove the Alodine?
3=2E Do you know of any reference sources?
4=2E Got any other ideas?

Thanks
Charles Caswell
Process Lead, Printed Circuit Board Dept=2E
Frontier Electronics Systems

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