Another cause of photoresist adhesion problems is metal contamination of the
photoresist.  This occurs at the coating mill.  I believe DuPont contracts
with a coating mills to do this work in different regions of the world.  In
other words, the coating may not be done by DuPont.

By Coating I mean the process of spreading the liquid photoresist between
the two layers of plastic, and rolling it on a tube.

This problem was verified by my company in a past life using a SEM to detect
the Metal in the resist.  DuPont never admitted the cause of the problem was
theirs until we confronted them with SEM data. I was pretty upset that
DuPont blamed my shop for the adhesion problem (and every other shop in the
area), when the KNEW it was their film.  For me, it was an excellent chance
to try materials from other suppliers.  This was many, many years ago.  I am
sure DuPont has changed in many ways since then.

How can metal contamination in the film cause poor adhesion?  Glad you
asked!
In the Photoresist there is an adhesion promoter.  It is a long organic
chain with one end of the chain that really likes metal.  When the adhesion
promoter sees the copper on the board... it grabs and holds on to it.  Now
when there is metal in the photoresist, the adhesion promoter grabs onto the
metal in the film, and NOT the copper on the board.


George Franck
Raytheon Systems
Falls Church VA
"My Opinions are just that."
.... as are my feelings and past recollections... Raytheon just doesn't have
anything to do with them.  Really!... Just ask one of their Lawyers.


-----Original Message-----
From:   TechNet [mailto:[log in to unmask]] On Behalf Of Francis Lai
Sent:   Tuesday, July 13, 1999 3:29 AM
To:     [log in to unmask]
Subject:        Re: [TN] RV: Dry film adherence problems

> CIPSA wrote:
>
>
>
>
> Dear Sirs,
>
> The reason why we send this e-mail is because we are having
> problems of adherence of our dry film Dupont 4615.
> The problem always appears beside the track/pads, and in the final pcb
> you always can see a bigger track, because the adherence of the film has
> not good and some Sn/Pb has get on the base copper (the film has not
> protect correctly the base copper, beside the track).
>
> We have done the following corrective actions and there has not been
> any success at all:
> 1. We have increased the lamination temperature from 105 to 115ºC.
> The presion is about 4 bars. The lamination rolls speed is about 1,6-2
m/min.
> 2. We have checked the pH of the revelator solution and goes from pH
> 11 at the beginnig to 10,4 at the end of the solution live.
> 3. We are quite sure that is not a electrolitic line problem, because in
the
> same bath position, we have panels with and without problems.
> 4. We have checked all the insolation parameters and everything is OK.
>
> What we are doing now, is changing from Dupont film 4615, to 215.
> Maybe, it will solve the problem, but we don't know the cause of our
problem.
>
> Does anybody knows the cause of our problem ???
>
> Thank you in advance for your colaboration.
>
> Albert Varon
> Quality Manager.
>
>
> **********************************************************
> CIRCUITOS IMPRESOS PROFESIONALES,S.A..
> Pol.Ind.Els Bellots C/de l'Aigua, 28
> 08227 TERRASSA (Barcelona) SPAIN
> Apdo. de correos 597-598
> Telf. 34.937856793 Fax 34.937861905
> **********************************************************

Dear Albert :

It sounds like exposure problem. Probably exposure time for dry film was too
short.
or the film is not proper.
I recommend you to check your exposure time and the film you use (the track
width
on the film).
Please correct me if I am wrong!!!!!

Francis