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December 2004

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From:
Pete menuez <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Pete menuez <[log in to unmask]>
Date:
Thu, 16 Dec 2004 20:53:30 -0500
Content-Type:
text/plain
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text/plain (78 lines)
Bill,

Positive etchback or etchback, as you know, is where the resin in the hole
is removed (commonly by plasma etch)  thus exposing the top and bottom of
the pad.  This exposed surface will be plated and you end up with a 3 point
connection, the top, front and bottom of the pad.  If we were talking lumber
this is the equivelant of a tongue and groove joint.

No etchbadk is when you drill a hole and don't remove any resin.  Panels are
run through a desmear cycle that removes any resin that might have 'smeared'
on the surface of the pad. (This is really hard to explain without
pictures). Now when the hole is plated the plating will only attach to one
surface; the front of the pad.  Another wodworking term. This would be the
equivalent of a  butt joint.

So imagine looking at a cross sectional view of a hole with no etchback -
The resin and copper are in the same plane. When the panel is run down the
electroless line one of the chemistries is micro-etch.  The micro etch is
desiged to remove copper. You can imagine (I hope) that when a panel with no
etchback (butt joint) goes through the micro-etch the copper some  of the
pad will be removed.  So the copper pad will be recessed slightly - below
the plane of the resin.  (No woodworking term) This is negative etchback.

Having said all of this and re-reading I decided to find some pictures on
the web.  (I just did a Google Search - I know Delson is a lab but I am not
associated in any manner. )

There are  pictures of both Positive and  Negative etchback.

http://www.delsen.com/gallery.html

Hope this helps.

pete

Click on this link and there is a picture titled Negative Etchback.

>From: Bill Dworak <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>,              Bill Dworak
><[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] I have a question
>Date: Thu, 16 Dec 2004 15:36:08 -0800
>
>Hi everybody I have a question that I hope is not a stupid one that I was
>just asked it is about the etch back process.
>What does a positive etch back mean? And what does a Flush etch back mean
>and what is the typical spec on these?
>I know what etch back means but not up on the two of these??? Please
>forgive me I am just a sales guy.
>  Thank you in advance.
>
>    Bill Dworak
>
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