Jac,
Thanks for your reply.
Concerning alternatives,we are running in our company in production OSP and
ENIG apart of HASL.
As a manufacturer of PCB we are applying finishing according to the customer
request.
Most of assemblers are stating " I do not care how you call it as long this
is flat and run through my assembly line as tin-lead finishing".
I spoke with a lot of manufacturers of PCB about the manufacturing side the
the finishing ( Omnicron,Alpha-Level etc) .The cruicial point is good
cooperation between the manufacturer of PCB and the assembly people.As
manufacturer of the board I can control my process,but what the assembler is
doing,how long and under what conditions the boards are stored is complety
out of my control.This is very painfull point.
Coming back to your remarks,as you stated,the crucial point are registration
problems.What do you mean 100% registration? For photoresist 2 mills
missalligment is normal nad for LPI even 4 mills.So if deviation are in
opposite directions this requires 6 mills overlaping.
Another point is the issue of tracks highness:some of our customers insists
on 1 oz base copper and 35 microns plated copper inside the holes,what lead
to plated copper 45 micron on the surface.Together it lead to 75-80 micron
high tracks.lamination of such tracks to avoid leacking of chemistry is not
simple.We tried 2 and 3 mills photoresists applied with vacuum laminator,but
stripping chemistry still infiltrated along the tracks.
regards
Edward
Edward Szpruch
Eltek , Manager of Process Engineering
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: Jac Kroeker [SMTP:[log in to unmask]]
> Sent: ד ספטמבר 15 1999 18:16
> To: [log in to unmask]
> Subject: Re: [TN] Surface finishing -Reply
>
> Edward;
> Selective solder stripping is not an easy process to do consistently well.
> However in my opinion and the opinion of the customers that are prepared
> to
> pay for the added cost it is a superior finish to HASL or HASL
> alternatives. Our next best option is omikron white tin. What is your
> opinion of the HASL alternatives currently available? ENIG, SILVER, WHITE
> TIN, OSP.
>
> To answer your question below.
> I don't think the type of dry film photoresist is an issue. We use Dupont
> 9600. We found better results with a thicker emulsion than normal. 2
> instead of 1.5 mil. This will help to eliminate your leaking problem.
> Now you must be prepared to cheat a little.
> Unless you can produce 100% perfect registration at all stages of
> manufacture, you will have either bare copper at the pad edges or reflowed
> solder under the mask. We do an expansion/contraction of the solder
> mask/solder strip film which leaves a small annular ring of solder under
> the mask. Size of the ring will depend upon your registration abilities.
> Reflow the tin/lead after masking.
> If you are proceeding with further testing, I will appreciate your
> comments.
> Jac Kroeker
>
> At 10:34 AM 09/15/1999 +0200, you wrote:
> >Hi Jac,
> >I am just wondering how your selective stripping is working?Probably you
> are
> >using selective masking ( photoresist) to protect the areas destignated
> for
> >reflow.What kind of photoresist are you using and what about overlaping
> >between tin-lead stripped pattern and solder mask pattern?
> >In the past we made trials and we faced the following problems:
> >1) leaking of tin-lead stripping solution along lines.This resulted non
> >clear boundary between the sections that were destignated for reflow and
> >those destignated to be covered by solder mask.
> >2) as result of the previous,we got exposed copper ar the boundary of the
> >"reflow side" and tin-lead on the "solder mask" side.
> >Regards
> >
> >Edward Szpruch
> >Eltek , Manager of Process Engineering
>
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