All,
After reading all the responses which are all right on the mark, I wanted to
add a few more comments for the record and because business of PTH
reliability is the heart of the interconnect business.
1. The majority of etchback requirements go back to the military prints of
the 60's and 70's when copper plate was Pyrophosphate with an elongation of
1-2%, innerlayers where built with std foil copper and material TG's ranged
from 110C-125C. During this time, I saw many, many, thermal cycle
reliability reports by the late Roger Wild of IBM Owego that showed etchback
to have better reliability. I might have some of these in my attic but it
might take another decade to find them. Steve Korchynsky, who is now
retired (worked in Owego for 30 years) could shed some more light, if anyone
is interested. However, that being said, the results with pyro copper and
etchback were just barely beyond the 100 cycle thermal shock CYCLE
requirements in MIL-P-55110.
2. As the demand for more reliability increased, copper plate changed to
acid with elongation around 20%, foil changed to high temperature
elongation, laminate T/G increased to 170C,and desmear migrated to plasma.
3. Therefore, with so many variable changes, comparing data/reports from a
long time ago to today is next to impossible. The only way to answer the
question is the run a controlled reliability experiment with your design,
your material, your suppliers, etc.
4. In the last 3-4 year I have run IST samples with and without etchback
with the following results:
a. For internal layers 1 ounce and above there is no difference in
reliability. They both lasted a very long time.
b. For internal layers with 1/2 ounce copper and electroless copper,
etchback was much more reliable. The 1/2 copper with conventional
electroless copper lines typically ends up with negative "copper etchback"
in the hole and this results in lower reliability during multiple thermal
cycling. If the 1/2 ounce copper does not have negative "copper etchback"
the hole etchback is not a factor.
Summary: From my experience with today's materials, hole etchback is not a
major factor in hole reliability except for internal layers less than 1
ounce. The only good way to answer the question based on a specific design
is to make some IST, HATS, etc coupons with and without etchback and take
them both to failure.
Mike Hill
Colonial Circuits
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]]On Behalf Of John Perry
Sent: Friday, March 30, 2007 11:25 AM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Etchback vs. Desmear
Thanks Mahendra,
Would anyone agree with the statement that I read in a tech paper that
etchback is performed less frequently on standard materials due to the
advances in performance of desmear chemistries?
John Perry
Technical Project Manager
IPC
3000 Lakeside Drive # 309S
Bannockburn, IL 60015
[log in to unmask]
1-847-597-2818 (P)
1-847-615-7105 (F)
1-847-615-7100 (Main)
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Gandhi,
Mahendra (Space Technology)
Sent: Friday, March 30, 2007 11:08 AM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Etchback vs. Desmear
John,
Look up TP 119, 120, 273, 377, 393, 616, 670 and 943. Also WC7-123, and
WC3-37.
Mahendra
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of John Perry
Sent: Friday, March 30, 2007 8:56 AM
To: [log in to unmask]
Subject: [IPC-600-6012] Etchback vs. Desmear
Hi All,
I've been asked as to whether or not IPC has any technical papers or
data sets that discuss etchback vs. desmear. I am going to look through
some of our past Conference Proceedings to see if we have any past
papers but I was wondering if anyone on this forum can comment on the
topic or perhaps recalls a past paper or study.
Thanks,
John Perry
Technical Project Manager
IPC
3000 Lakeside Drive # 309S
Bannockburn, IL 60015
[log in to unmask]
1-847-597-2818 (P)
1-847-615-7105 (F)
1-847-615-7100 (Main)
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