In a past life, when I was director of a PCB factory, we also made Al
front panels. These were slightly different, because the dying (3
colours) was selective and was done between anodising and what Rudy
calls hydrating (we called it sealing, because it was an essential part
of sealing the dyes into the anodic layer). Without it, the dyes would
leach out and smear slightly if the panel was subsequently wetted.

We used a special grade of Al sheet with a fine finish for panels,
because appearance was important. With "ordinary" sheet, you will get
blemishes which may or may not be important for you. No abrasive was
used, as any implanted particles caused visible blemishes. Cleaning was
done in a heavily buffered alkaline detergent solution which did not
attack the surface, followed by a cathodisation bath which did,
producing a matt finish. Deep anodisation took 30 minutes in H2SO4
solution. The image masks were silk-screened on, using a cellulose type
pale yellow ink, easily stripped in a methylene chloride/amyl acetate
mixture. Dyeing was by immersion in cold aqueous solutions. Sealing was
more serious than Rudy mentioned: 30 minutes in boiling DI water.

For prototypes (single colour), we had a slightly different process.
After anodisation, we dyed the whole panel and then applied a dry film
photoresist (solvent type). After exposure and development, we leached
out the dye in a dilute caustic solution, stripped and sealed it. It was
not perfect but adequate, and easier, cheaper and faster (we kept a
small stock of photoresisted panels).

However, anodisation may not be necessary in your case: you may obtain
better and cheaper results by a chemical conversion coating, such as
phosphatision or chromatisation, which is done by immersion. It is
cheaper and quicker. Many (but not all) of the black radiators for power
semiconductors are dyed phosphatised aluminium. (This is why the colour
leaches badly in saponifiers, which would not happen in a properly
sealed anodic coating.) These coatings are extremely adherent, although
less mechanically resistant to scratching.

Brian

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------