Re: [CAD_CAM_EDM_DRO] Re: Stepper motor speeds

In a message dated 11/6/2002 10:23:05 AM Central Standard Time,
antonio-ximenez@... writes:

> How do you make the plated holes ????
>

This is done BEFORE etching. The holes are ALL drilled first, then the board
is "sensitized" in a bath of chemical that makes the ENTIRE surface
conductive, i.e., the "walls" of the holes, too, electrically-connected to
the copper on both surfaces. Then the board is ELECTROPLATED in copper.
Yes, this not only puts copper INSIDE the holes (on the walls of the holes),
but it THICKENS the copper surfaces, too. Thus, some (all?) PC-shops use
"half-ounce" copper, since it gets thickened when "plating-through".

Then, a "negative" image is laid on, so that the exposed copper is the
"tracks" you want, and then that is "solder-plated" (yes, a tin-lead alloy is
actually electro-deposited on the exposed copper).

Then this image-resist is removed, and . . .

Then that is placed in an etchant-bath (I am NOT a PC-manufacturer, so I am
not sure, but I THINK they us ammonium persulfate. NOT ferric chloride, as
we "one little PC every few weeks" folks use.) This etchant attacks copper
just fine but does NOT "eat the solder".

Once the "unwanted" copper is etched away, the boards are "reflowed", meaning
HEATED to the melting point of the solder, so that "solder-plating" flows
nicely over the copper tracks and "rounds over, nicely".

Then, epoxy "solder-mask" and then "silk-screening" showing which transistor
goes which way, where, etc.

Sorry, I have NO clue how the process for "multilayer" is done, at least not
sufficiently to describe it here!

Lotsa luck! Jan Rowland, Troll


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