Pete
you wrote:

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
----- Original Message -----
From: "Pete menuez" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, December 16, 2004 8:53 PM
Subject: Re: [TN] I have a question

On the topic of etchback/desmear - this is all based on the degree of resin
removed.

Negative Etchback can occur in both a desmear or an etchback process.
Depending on dwell time in microetch.

It really does not have a preference for desmear or etchback - it will etch
the copper foil on the innerlayer.

On the explanation of no resin removed - this - 90% of the time will cause
innerlayer sep - due to the fact that you are now trying to plate over
resin. If it is electrolized in the electroless (smear/resin) - this usually
does not hold up to the force applied from the stress of the copper deposit.

In woodworking terms - bad joint!


Permanganate etchback/desmear is still the choice of processing - unless the
fab shop is working with exotic material or usually with high Tg material
and small through-holes will they go to plasma.


regards

Rich Fudalewski

> 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
> >
> >---------------------------------------------------
> >Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> >To unsubscribe, send a message to [log in to unmask] with following text in
> >the BODY (NOT the subject field): SIGNOFF Technet
> >To temporarily halt or (re-start) delivery of Technet send e-mail to
> >[log in to unmask]: SET Technet NOMAIL or (MAIL)
> >To receive ONE mailing per day of all the posts: send e-mail to
> >[log in to unmask]: SET Technet Digest
> >Search the archives of previous posts at:
http://listserv.ipc.org/archives
> >Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16
> >for additional information, or contact Keach Sasamori at [log in to unmask]
or
> >847-615-7100 ext.2815
> >-----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
> -----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------