A couple of questions:
How is adhesion after thermal stress? Is this a real problem or just an odd
occurance that has someone nervous/curious?
What is the etchrate of the bath?
A couple of comments:
Usually, we can see a condition called 'spearheadding' when an over-etch
condition is present on our products. The conductor length appears to be
sticking out into the hole as normal, but the width of the conductor is
about 1/2W and gradually increases as you move closer to the hole wall where
it is close to original thickness.
Another question may be has anything caused the material to swell into the
hole instead of shrink the conductor. A sweller chemistry from desmear, if
permanganate chemistry is used, can be over done to cause some materials to
swell into the hole wall.
Back to the etchrate question. We have several types of copper etchants in
production. One, non-persulfate based, is used on our electroless copper
line and has an etchrate of 30 microinches per minute. The process has been
set up to remove 50-100 microinches of copper. The chemistry, time and
temperature have been determined to maintain the total remove depth.
We also have another bath, persulfate based, used in several final finish
processes. If given that the persulfate and sulfuric acid chemistry are at
pre-established levels, the temperature and the copper concentration will
dictate the etchrate of this bath. Little or no copper in the bath will
reduce the etchrate tremendously. Too much copper and the rate will be to
aggressive. Its etchrate is 40 microinches per minute at a temperature of 95
degrees F and a copper concentration of 11g/L. The time is adjusted to reach
the desired etch depth. A bath with no copper in it will have an etchrate of
approx. 15 microinches per minute. Often a new bath is 'doped' with leftover
previous chemistry from the same tank, or copper sulfate pentahydrate is
added to provide the needed copper.
I hope this helps. Offline I can be reached at 602-276-1600 to talk of this
til I'm blue in the face (pun intended).
Russ Burdick, process engineer, printed circuit mfg.
>From: "Stephen R. Gregory" <[log in to unmask]>
>Reply-To: "TechNet E-Mail Forum." <[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] Inner Layer Issues...
>Date: Thu, 8 Nov 2001 21:12:38 EST
>
>Hi Everybody!
>
>I got a email from Rene Lopez who has a problem that want's looked at by
>the
>group. I've posted two pictures up on my web page at:
>
>http://stevezeva.homestead.com/
>
>Rene is having a bit of trouble getting posts from the TechNet, and I don't
>know if it's been solved yet, that's why I've included Rene's email address
>here, do a "reply all" so Rene receives your replies.
>
>(Thanks Rene for being patient with me...)
>
>-Steve Gregory-
>
>I've pasted Rene's email to me below:
>
>Hi Steve,
>
>Here are the two pics of concern. These boards were processed thru a sodium
>persulfate solution for 45 seconds at 72 F. We know that if we reduce the
>time in
>solution we may have problems on the surface of the board/adhesion issue.
>
>More time in solution may cause more negative etchback.The material next to
>the
>innerconnects is acrylic. Tank is agitated with enductors as opposed to air
>spargers.
>
>It also has good side to side mechanical agitation. Have tried running the
>tank with the enductors off and with them on with same results.
>
>As noted on the pictures, there is some sort of rounding off of the
>innnerconnects. Does anyone know what causes this and give some input on
>how
>it can be reduced or eliminated?
>
>Any input from your peers would be of great help.
>
>Thank you very much,
>
>-Rene A. Lopez-
>
>
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