Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!wugate!uunet!ingr!phil
From: phil@ingr.com (Phil Johnson)
Newsgroups: sci.electronics
Subject: Re: Re^2: Through-plating PCB's
Message-ID: <6329@ingr.com>
Date: 1 Sep 89 15:47:25 GMT
References: <4003@csd4.csd.uwm.edu> <10040019@hprmokg.HP.COM> <6684@stiatl.UUCP>
Reply-To: phil@ingr.UUCP (Phil Johnson)
Organization: Intergraph Corp. Huntsville, Al
Lines: 58

In article <6684@stiatl.UUCP> john@stiatl.UUCP (John DeArmond) writes:

>Plated-through holes are done BEFORE etching.  The board is drilled on
>an NC drill.  Next the holes are coated with a conductive substance and 
>then the board is plated.  Metal is deposited on top of the conductive
>coating.  Then the board traces are applied and etched.

It is true that low quantity production houses may use the removal process,
but as the cost of this method increases (cost of copper, toxic chemical
handling, etc) even low quantity houses are switching to deposition methods.

Briefly the deposition process consists of four steps:

  NOTE: I use the term VIA for both true VIAs and hole.

1. Coating a substrate (fiberglass, pheno, ceramic, or whatever) with a photo-
   resist (either positive or negative - production house's choice).

2. Photoprocessing the trace layer.  This is the same as in the etch process.
   A pictue of the trace layer is made on the photoresist.  Once the layer of
   processed only the traces, etc are on the board.  These areas serve as the
   receptor of the next step.

3. A conductive material is deposited onto the receptor material.

4. The layers are then bonded together and the external layers and VIAs are
   processed.

The main deviation from the description is in step 1.  Some houses silkscreen
the patterns onto the substrate with receptor material rather than do the 
photoprocessing on the substrate.
 
>
>While the process is somewhat tedious and particular regarding chemistry 
>control, it is well within the capabilities a well-equipped prototype 
>or hobby shop.  Kepro, among others, sells desktop equipment and chemicals.
>Check your EEG or EBG for an address or phone.
>
>John De Armond, WD4OQC                     | Manual? ... What manual ?!? 
>Sales Technologies, Inc.    Atlanta, GA    | This is Unix, My son, You 
>...!gatech!stiatl!john    **I am the NRA** | just GOTTA Know!!! 

The Kepro lab is not what I would call an inexpensive hobby shop system.  I
haven't looked at it for several years but believe it cost several thousand
dollars to have it expanded to process anything but low density two-sided
boards.

I have made many two-sided boards at home, but would not try multilayered
boards or plated-through Holes.  The plating chemistry is more than my than
my CONVIENCE FACTOR can handle, so I send this type work outside.  There is
small prototype houses that will do this work cheaper than it can be done at
home.


-- 
Philip E. Johnson                    UUCP:  usenet!ingr!b3!sys_7a!phil
MY words,                           VOICE:  (205) 772-2497
MY opinion!