Brian,
I think you should check the chemical resistance data on Polyimide. The acrylic adhesive
might break down in high pH, but the resist strippers we use are >pH12 and they never
attack the Polyimide film.
I am currently testing new resist stripping solutions and have left Polyimide in the
solution for hours at elevated temperatures with no obvious breakdown of the film.
Chuck Brummer
Acuson
[log in to unmask]
Brian Ellis wrote:
> Whoa, Kelly! Saponifiers and polyimide flex are a big No! No! combination. That is,
> unless you want to etch holes in the substrate. OK, I may exaggerate, but polyimide is
> chemically degraded at pHs above about 9,5.
>
> My recommendation: water-soluble flux/paste (not too aggressive), hold flexes in
> fixtures with stainless springs looped in holes for that purpose, so that they remain
> taut, load fixtures in baskets at c. 20° to the vertical, high-throughput batch washer
> (not dishwasher, unless you have very low throughput of just a couple of circuits per
> hour), dry in machine with rotary air knives. This will comfortably meet all specs
> without damage.
>
> Brian
>
> "Kelly M. Schriver" wrote:
>
> > Hi Nancy -
> >
> > To begin with, the cleaning media is driven by the particular flux you are
> > using. This, in turn, will drive the issue of what equipment you may be
> > able to use for the process. I have had good success removing RMA residues
> > from flex circuits with quite a number of blended solvents in vapor
> > degreasers and conveyorized spray systems. Size of the flex assembly must
> > obviously be considered - there are a number of suppliers who can provide
> > cleaning baskets to restrain small flexes for processing thru conveyorized
> > cleaning systems. Manual cleaning would not be my first choice if I were
> > dealing with a high reliability article, particularly if it were to be
> > conformal coated.
> >
> > Another possibility might be one of the saponifiers, in either a heated bath
> > or a "dishwasher" type system.
> >
> > If you are not currently using a low residue ("no clean") flux, might that
> > be a possibility? If this is a consideration, and you plan to conformal
> > coat or use adhesives on the assembly, be sure to verify full compatibility
> > of the flux residues and the specific coating material you intend to use
> > before proceeding.
> >
> > Contact me directly if I can be of assistance.
> >
> > Regards - Kelly
> >
> > -----Original Message-----
> > From: Nancy M. H. Holloway <[log in to unmask]>
> > To: [log in to unmask] <[log in to unmask]>
> > Date: Tuesday, January 04, 2000 10:57 AM
> > Subject: [TN] cleaning flex circuits
> >
> > >TechNet,
> > >
> > > What is the best technique to clean flux off of a polyimide flex circuit
> > >after population? Thus far, we have been cleaning the flex circuits with
> > >alcohol but it is time consuming and tedious. We use a machine to clean
> > >rigid boards, but I am hesitant to use it for our flex circuits. How are
> > >you all cleaning your soldered flexible printed circuit boards.
> > >
> > > Thanks,
> > > Nancy
> > >
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