In a message dated 2/26/99 8:13:22 PM Pacific Standard Time,
[log in to unmask] writes:
<< Steve,
How much variation? I was a under the impression that 106A was self
limiting and that it was more of a manufacturing philosophy immersion vs.
conveyorized. As a user of boards this is what I've always heard from the
manufacturer. Evidently this might not be correct? Could you elaborate?
Best Regards
Corey Peterson >>
Hi Corey!
Sure...now what I'm about to pass on is what I've read over the years
here on the TechNet, not totally from direct experience. Most of my experience
with -106 has been in a water soluble, organic acid, solder to dirt type of
environment...and that's why I prefaced what I said with; "I've heard of
people having problems..." Here's a couple of blasts from the past from the
archives, and a differing view on the "when bed of nails testing should be
done" issue. From my experience though, I would occasionally see solderability
issues even in a water soluble environment, it would only occur when I was
dealing with pitches down around 15-mil ( ya gotta admit there's not much
paste and flux printed on a 15-mil pitch pad), but they were relatively minor.
I have seen fabs that I could see with my own eyes that had a varying coating
thickness, I could tell it had been done by dipping by the runs in the coating
surface that I observed on the panels...they were all towards one edge as if
they were suspended from the other end while drying during the coating
process. So it would just seem that if one were using very mild fluxes, you
could easily have some problems if the OSP coating was too thick and wasn't
consistent.
-Steve Gregory-
Date: 1 Feb 1996 16:29:46 -0500
From: "Greg Bartlett" <[log in to unmask]>
Subject: Re: REQ- Info on Entek Plus/
To: "[log in to unmask]" <[log in to unmask]>
Jon,
Excellent note regarding Entek Plus on flex.
We've used both Entek Plus and MacDermid M-Coat Plus for a couple of years
now with no-clean chemistries with generally no problems. (We tried a
couple of other formulations, as well.) A couple of initial problems,
though:
1) Defects (opens) at CBGA sites because of "locally thick" OSP coating.
The supplier claimed that the coating cannot exceed a certain thickness,
but I believe that this is on well-controlled flat coupons. On our boards
you could see how some of the pads developed a "shellac-like" finish
because of the excess thickness - lab measurements indicated that it was
~3x the max thickness. We attributed this to both the OSP application
process and the via geometry, which allowed residual coating to seep onto
the BGA pads toward the end of the process. Changing the application
process worked.
2) We found that the OSP-coated boards had to be *absolutely dry* prior to
bagging and shipping. Any moisture left in the vias would seep out and
destroy the OSP coating (it turns black).
The only real concerns to date are the lack of a good topside PTH fillet
and lack of good solder spread on pads.
Also: we have had customers question the reliability of exposed copper,
but there is a large volume of data within the industry which helped us to
successfully address these concerns.
Regards,
Greg Bartlett
Mercury Computer Systems
Chelmsford, MA
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Subject: Re [2]: Entec 106
Author: [log in to unmask] at !INTERNET
Date: 11/4/96 6:40 PM
Hi Ron,
Solderability:
- Solderability of OSP is affected by many factors. (Enthone- the maker of
Entek should be able to answer most of your questions) You can use
J-STD-003 to test the solderability of PCB.
Cleanliness
- In case you have a misprint during paste application, you should make sure
the cleaner chemistry compatible with your OSP.
Joint Integrity
- There is an interesting paper presented by Motorla at 1994 SMI Titled
"Manufacturability and Reliability of Products Assembled with New PCB
Finishes"
by Kingshuk Banerji and Edwin Bradley
Coating Thickness
- Entek 106+ is about 0.2 to 0.5 microns
Hope this helps
Michael Yuen
******************************************************************************
***************
Subject: Entec 106
Author: [log in to unmask] at !INTERNET
Date: 11/4/96 12:54 PM
Jeffery Harry, would you please expand on the "major problems" you
have seen by running Entek 106 in a dip mode.
Peter Blokhuis
PC World
[log in to unmask]
******************************************************************************
****************
If you use Entec 106, make sure that the PCB supplier has an in-line
process. Dip tanks will cause major problems. Also the PCBS need to
be thoroughly dried before packaging. If not, you will have
solderability problems.
Jeffrey_Harry @ 3mail.3com.com@ ugate
******************************************************************************
****************
From: [log in to unmask] [SMTP:[log in to unmask]] =
Sent: Friday, December 05, 1997 2:36 PM
To: [log in to unmask]
Subject: Re: [TN] entek plus process
Matthew:
From my perspective, the question that needs to be addressed FIRST is
where in the process is the ENTEK applied to the board.
1) ENTEK BEFORE or AFTER Bare Board Test By itself, ENTEK is an
insulator. Therefore, if it is applied PRIOR to bare board testing, the bare
board test probes can create "false opens" due to residue buildup on the tips
of the probes. This might indicate that ENTEK AFTER bare board test would be
better. On the other hand, a mild microetch is used to prepare the surface
prior to ENTEK application. If the dip process is used and the microetch is
fresh (i.e. strong solution), excessive etching can result. This can result
in circumferential barrel voids at the knee of the holes, where the copper is
the thinnest. If ENTEK is applied AFTER TEST, this type of defect will not be
discovered until the board has been populated with expensive components. Some
people subscribe to the policy "NO chemical operation shall be performed AFTER
bare board testing". Each vendor's process and controls must be evaluated to
assess the likelihood for this type of failure.
2) In-line vs. Batch In my opinion, in-line would be better and more
repeatable, if the total volume of boards that the vendor processes warrant
the equipment expense. Properly managed, the dip process will work.
3) "Spotted" Boards:Another "problem" to look out for is moisture spotting
during shipment. ENTEK uses a DI rinse in the process and, if vias are small
(0.013" dia.), moisture can be trapped inside the barrel of those vias.
Placing the "drip-dried" board in a plastic bag for shipment, can result in
residual moisture STILL residing in the bag. Shipment of the boards to the
final destination (shipping vibration, change in temperature, etc.) causes the
moisture to migrate to the inside surface of the bag and, in turn, back onto
the board. The thickness of the ENTEK on the board will be reduced where there
is intimate moisture contact. The appearance looks like "water spots" on a
drinking glass. They COULD result in localized ENTEK "voids" and potentially
cause solderability problems, if the boards are left on the shelf for an
extended period of time.
One test for "dryness" of a board is a deceptably simple one:
a) Take a piece of colored construction paper (or the cardboard stiffener on
the back of a pad of paper) that will darken when exposed to water and place
it on a flat surface (e.g. table).
b) Take a "dry" board and firmly slap the face of the board onto the
cardboard. If it shows dark spots on the cardboard when the fab is removed,
the fab is NOT dry and could caule spotting during shipment.
My suggestion is to have the boards BAKED after ENTEK to eliminate this
potential problem. I advocate the use of ENTEK for fine pitch QFP designs,
because of the resultant pad flatness, as compared with HASL.
However, it does have some "side effects" to watch out for. It is NOT the
"panacea for all ills", but it is better than some of the alternatives in
certain designs.
The above opinions are my own, etc.,etc., etc. =
Good Luck!
Bill Fabry
Plantronics, Inc.
(408) 458-7555
e-mail: [log in to unmask]
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