WOW, in one TechNet posting, you ask us chemical vendors to explain all the
hocus pocus we've developed over 30 years.   All I can say in our defense is
that the frequency of voids in pwb processing now must be less than one in
ten million holes, since shops preform to less than 0.1% of void failures of
boards having 10,000 holes each. Well, here goes:

1. The mechanisms of colloidal suspension between the very small
tin/palladium traditional catalysts and the suspension of carbon particles in
the direct metallization process is different (we supply both carbon based
direct metallization and traditional electroless copper.)   The carbon
particles are processed with a surfactant so the "marbles" don't agglomerate
and form "baseballs" which could no longer be held in colloidal suspension.
 We analyze the colloidal size for our customers who buy the "Blackhole"
carbon black based direct plate process from us. I believe the graphite
carbon vendors formulate similarly.  Particle size is not a major concern
with our traditional palladium based catalysts for electroless copper
plating.  Finally, there are vendors of palladium direct plate systems which
are chemically a cross between  electroless plating and carbon based direct
metallization.  One of those vendors needs to comment on their "conditioning
chemistry" as the colloid functions as the current conductor in
electroplating rather than catalyst in electroless copper.

2. Printed circuit board holes are not all the same.  Double sided boards are
plated as drilled.  I prefer to consider the epoxy/glass hole wall as "water
hating"  - (hydrophobic), even after the heat of drilling.   The conditioner
(surfactant) makes double sided holes water loving (hydrophilic).  ALL the
following plating steps are water based solutions, so printed circuit holes
had better be water loving!  

Multilayer holes are "desmeared" to remove any electrically insulating epoxy
drill smear across the interior copper surfaces (posts or interconnects).
 Today, hot alkaline permanagante solution oxidizes away some (0.1 to 0.3
mils) of the hole wall epoxy to be sure the interconnects are squeaky clean
for the subsequent copper electroplating.  This oxidation leaves the hole
wall epoxy with both a residual charge and creates a pock-marked surface that
tends to be hydrophylic (water wettable).

3. Cleaner (to remove fingerprints, drill machine oil, shop airborne dirt,
etc) is only important on double sided boards since permanganate is good at
removing that stuff through oxidation, too.  More multilayers are made today
than double side in the US.  But, I think all chemical vendors still put in
some cleaners as insurance to be sure both double sided and multilayer boards
can run in the same plating line.  

All of us electoless plating suppliers use "conditioner" to get maximum
tin/palladium colloid through the acceleration bath (stripping tin to make
palladium catallytically active) and into the electroless copper.  We want
electroless copper plating to initiate in 15 to 60 seconds after board
immersion.   

The conditioner in a carbon based direct metallization has an even bigger job
as it helps bind the carbon to the hole wall through the direct plate
microetch, board drying, dry film lamination, alkaline development, board
drying/inspection, pattern plate soak clean, and pattern plate microetch.
 Finally, the carbon is conductive enough to allow copper electroplate to
form a copper eyelet in the hole.

3. Various chemical vendors use different types of surfactants - anionic,
cationic, amphoteric, etc - as we have a variety of jobs - colloidal
suspension, making surfaces hydrophilic, etc.

4. The microetch in board manufacture is used to make clean copper for the
subsequent addition of more metal - ususally more copper as we build traces
or plate the copper eyelets in holes.  

A microetch is used in standard plated through hole lines to remove the
conditioner (surfactant) from the foil surface and the post/interconnect.
 Thick surfactant layers cause weak copper-to-copper boundaries which may
separate in thermal cycling (solder assembly or power up/down in use).  These
copper-to-copper failures show up as intermittant opens in the circuitry
-TRAUMA FOR THE USER,  DEVICE SELLER, OEM, ASSEMBLY SHOP, BOARD FABRICATOR,
AND OF COURSE - CHEMICAL VENDOR.  In polite pwb company - don't say
intermittent opens, it's kind of like the b___ word at the airport metal
detector.

In direct metallization, the carbon (or tin/palladium on the surface)
interfers with dry film adhesion and subsequent circuit formation.  Of
course, carbon on the post/interconnect can lead to intermittent opens, also.

The microetch in both technologies undermines the colloid/carbon particle on
copper and "floats" it away from the surface.  I think all direct
metallization vendors ask that the particles be filtered from the
recirculating microetch to prevent particle re-deposition as the board leaves
the bath.  No physical removal of epoxy occurs in the microetch, so the
conditioner holds the colloid/carbon tightly to the hole wall.

Hope this helps.  Incidentally, your e-mail address "siue.edu" is quite
familiar to me as my son is finishing a degreee at "siuc.edu" - Southern
Illinois University at Carbondale.  Didn't know of a printed circuit
technology group at SIU Edwardsville - is it new?
 
Denny Fritz
MacDermid, Inc
Waterbury, CT
203-575-5740

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