First of all, you need to clearly define whether you have resin smear
causing what appears to be post-separation, or if you have true
post-separation. You need to carefully prepare a microsection and
LIGHTLY microetch the section using a solution of 10 mls ammonium
hydroxide, 10 mls of DI/distilled water, and 10 DROPS of 35% hydrogen
peroxide (or 10 mls of 3% hydrogen peroxide from the pharmacy). If you
have polished the section correctly and do not overetch the section, you
should be able to clearly see your electroless copper deposit (assuming
that you are using electroless copper and not a DM system). If there is
smeared resin, you should be able to see it using a backfield setting on
your microscope; if there is separation rather that smear you should be
able to see if it is between the electroless copper and the post
(innerlayer) or between the plated copper and the electroless.
1. In the case of resin smear: consult with vendors and verify that the
desmear chemistry and cycle is working properly. When using
permanganate desmear, solvent/sweller life is a very important part of
making this process work properly, as is by-product/residue levels in the
permanganate bath itself. I would recommend requesting SEM work to
verify proper resin attack and topography.
2. In the case of electroless to post separation: in a somewhat
decreasing order of likelihood: a) excessive catalyst concentration or
dwell time; b) excessive rinse time following microetch, catalyst, or
accelerator; c) poor microetch quality or quantity (I would recommend
30-70 microinches weight loss, depending on the weight of the innerlayer
copper foil - the heavier the innerlayer foil, the more the weight loss
should be); d) incorrect conditioner (some conditioners use
polyelectrolytes that are very large and rinse very poorly, leaving
deposits on the innerconnect; and e) permanganate residues (only in the
case of using a persulfate microetch).
3) When the plated copper separates from the electroless deposit, if
there is a severe photoresist developing problem you should see
problems with peeling circuits, etc. Generally this problem is caused by
poor pre-electrolytic copper plating cleaning - I have had much better
success when using a two-step cleaning process; an acid cleaner
(non-hydrochloric acid-based) followed by a light microetch (generally a
non-proprietary peroxide/sulfuric at 5-8 microinches). There are other
causes of this problem, but they are generally rare.
I would expect a wide variety of quality within the same date code, due to
process variables in drilling, desmear, and pre-plate cleaning. You can
expect to always have some resin smear when drilling FR-4 type
materials; if you have resin smear as well as nailheading, glass pulls or
other roughness in the hole, etc. then you need to look at your drilling
process. In my experience, even the very worst resin smear can be
cleaned up with only a few minutes in the permanganate - the additional
dwell time is there to provide either etchback or topography.
One last thing - if you're that worried about your suppliers cheating you,
you need to seriously re-evaluate both yourself and your suppliers. As a
chemical field service person for eight years, I can assure you that most
people are out only to do their job, and not screw everyone in sight - the
supplier can't be successful if the customer is not successful first -
otherwise how can the customer purchase the suppliers stuff? It is of
course possible that you need some new suppliers, as there are some
jeks around, but you need to realize that some of the fabricators aren't
necessarily straight shooters, either.
regards, Fred J.
>>> Ken Patel <[log in to unmask]> 10/14/97 06:14pm >>>
Fab Gurus,
I have seen post separation on my assembled board and also resin
smear. I
have few question in that regards.
(1)Can any one provide me the possible causes for the defects?
(2)How much is a variation for this kind of defects within a same date
code?
(3)What about the reliability of my assembled boards?
Also being new in fab business, can any one suggest books that talk
about
the fab processes and also that talk about possible causes. I am of the
opinion that I should know more about the fab than the fab supplier so
that
no one can try to cheat you!!!
I would really appreciate anyone's help.
Regards,
Ken Patel
______________________________________________________
Ken Patel Phone: (408) 490-6804
575 Cottonwood Dr. Fax: (408) 490-6859
Milpitas, CA 95035 Beeper: (888) 769-1808
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