Black hole process (MacDermitt) for PCB fab| 30 May, 2000
More and more PCB fabs are switching from chemical copper to what is called a "black hole" process from McDermitt.In this process a very thin layer of carbon is put on the base material instead of chemical copper. Can anyone tell me about the advantages and disadvantages of this new system in respect to chemical copper? Does anyone have some experience with using PCB's with this process? Are there any restrictions on the # of layers (ML4,6,8 or higher) that can be used with this process?
Re: Black hole process (MacDermitt) for PCB fab| 30 May, 2000
Dennis: Direct metalization is more of an European phenomena than a US one. Not to say that good things don�t come out of Europe. As background:
Direct Metallization. In circuit board fabrication, an alternative to electroless plating makes the non-conductive areas conductive to enable pattern plating on boards with a conductive material. In contrast to electroless copper, direct metallization can not be inspected for complete hole coverage - this occurs only after copper electroplate. Direct metallization processes are: (1) Easily conveyorized in horizontal process equipment, except palladium processes. (2) Use little, if any, hazardous chemistry - especially chelated copper that may be difficult to waste treat. (3) Operate fast - processing takes a matter of minutes, compared to ~ 90 minutes for the entire electroless plating line. Alternate direct metalization processes are: (1) palladium (e.g., EE-1, DPS, Crimson, ABC, etc), (2) graphite / carbon black (i.e., Shadow / BlackHole), and (3) conductive polymer (i.e., Compact CP, DMS-E).
From Coombs: Since PTH hole metalization constitutes only 2-3%, at most, of the total cost of manufacturing a PCB, the direct saving is small from water conservation, no noxious chemicals, improved panel handling, reduced waste treatment, lower labor costs, better productivity, etc.
US EPA funded a study of electroless process alternatives. Although the focus of the study was environmental impact, it includes useful information on Making Holes Conductive (MHC) processes. Much is available on line: http://www.epa.gov/opptintr/dfe/pwb/pwb.html
If the thought of printing a 400 page booklet makes your eyes glaze over, the National Service Center provides them free (order online). Consider: * EPA 744-R-97-001 Implementing Cleaner Technologies in the PWB: MHC * EPA 744-R-98-004a PWB Cleaner Technologies Substitutes Assessment: MHC * EPA 744-R-98-002 Alternative Technologies for MHC
Recognize that operating a DM line "builds character." � Care needs to be taken with processes leading up to DM, like: drills, re-points, number of hits, hole roughness, desmear, degree of etch back. � Aspect ratios, and hole sizes of the product require reconsideration. � As with any new process, the three main ingredients (ie, process engineer, chemistry, equipment supplier) have to mesh well for a successful process implementation.
Think about: � Reviewing your designs, make sure power and ground did not run up to your previous nonconductive, nonplated holes. � Level of experience your supplier has with DM? Have they gotten past their "teething problems"? Is this what they say, or what customers, similar to you, say? � If your supplier has a tendency to get a little negative etch back? If so, be aware that DM seems to go into this area and remain there, creating problems in getting under it to remove it as planned.
Earl: Are you lurking around out there? What�s to add?