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 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************