To all,
Besides having time to poke fun at Doug and offer Mike a chance to
practice on his comedic relief, there have been many valid points made
on what's the ultimate surface finish. Of course the correct answer is
copper. Unfortunately until nano-technology improves the current crop of
OSPs that is not a reality, but still should be the goal. I default to
HASL for all the aforementioned reasons, knowing full well the potential
assembly limitations with some designs. If someone asks me what is the
current finish that I would recommend where there would be no worries
other than potential cost disparities, I would say ENEPIG.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Thursday, June 02, 2011 10:01 AM
To: [log in to unmask]
Subject: Re: [TN] Best Board Finish - beyond gold
To illustrate Scott's point about HASL causing poor stencil gasketing
I've sent Steve a file I'm hoping he will post. HASL may look flat to
the naked eye but look at the second slide in the file I've sent and
you'll get a good idea of why stencil printing to fine pitch features is
a problem with HASL surface finish.
Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Post, Scott E
Sent: Thursday, June 02, 2011 12:33 PM
To: [log in to unmask]
Subject: Re: [TN] Best Board Finish - beyond gold
It can be really difficult to get solder paste to release consistently
on very fine features with HASL. Also, the domed shape of HASL can
cause poor stencil gasketing that leads to solder squeezing down the
sides of the land and bridging. Every company seems to have a different
threshold where they won't use HASL. I know some people won't use it on
boards that have 0402s and 0.5 mm pitch QFPs. I personally think HASL
is OK for those feature sizes but below that causes too much grief. In
fact, last month I ran an experiment using a board design with 0.4 mm
pitch QFPs and BGAs as well as some resistor arrays with very fine
apertures. I had the same board design with OSP and SN100 HASL. The
difference in print quality was dramatic even though the HASL boards had
what I consider very good HASL. I'd hate to think how bad the print
quality would have been with some of the variation we see in Pb free
HASL quality.
Scott Post
Staff Manufacturing Engineer
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana 46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Thursday, June 02, 2011 11:37 AM
To: [log in to unmask]
Subject: Re: [TN] Best Board Finish - beyond gold
Bob,
As for flatness: once a PCB has paste printed can you even tell what
the
finish is? I have never been able to figure out this flatness thing.
As for reliability I think solderability wins every time. Are you
telling
me these other finishes have better solderability than, well solder, as
found only in a HASL finish? Has anyone ever seen "Black Pad" with HASL?
There is no Ni so the P cannot be wrong, ever. Right?
I fell like a stick in the mud on my bias towards HASL, I am open to
ideas
here.
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob METCALF
Sent: Thursday, June 02, 2011 11:18 AM
To: [log in to unmask]
Subject: Re: [TN] Best Board Finish - beyond gold
When considering finishes, if the ultimate in reliability and surface
flatness are key considerations, you must give electroless nickel,
electroless palladium, immersion gold (ENEPIG) some consideration.
Regards,
Bob Metcalf
Western Regional Manager
Atotech USA Inc
1750 Overview Drive
Rock Hill, South Carolina 29730 USA
Mobile: 714-334-7667
e-mail: [log in to unmask]
Internet: www.atotech.com
Managing Director: Kuldip Johal
This e-mail and any attachments hereto are business documents of Atotech
USA
Inc. and may contain CONFIDENTIAL OR PROPRIETARY BUSINESS INFORMATION.
Unauthorized disclosure and/or use of information contained in this
e-mail
are prohibited. If you are not the intended recipient, you should
dispose
of it and not use, disseminate or copy this message or any other files
transmitted with it.
.
From: "Stadem, Richard D." <[log in to unmask]>
To: <[log in to unmask]>
Date: 06/02/2011 07:46 AM
Subject: Re: [TN] Best Board Finish - beyond gold
Sent by: TechNet <[log in to unmask]>
I agree with everything you say, Barbara. It sounds like you are now on
your
way to making the correct choice.
Stay away from immersion tin.
If you choose immersion silver, refer to both IPC 1601 and IPC 4553 for
storage and handling considerations. They can be managed.
The double-sided process can leave a slight reduction of solderability
with
immersion silver PWBs by the time you are ready to hand solder any PTH
parts, making that more difficult to do, sometimes.
That is why I asked.
Also, if you select Immersion Silver, make sure that your PWB
fabricator
has a good plating product, a well controlled process and some
experience
with it.
Ditto with ENIG. Especially with ENIG.
Regarding immersion silver, it is susceptible to environments that are
heavy
in sulfides, such as automotive exhaust, rubber processing, or paper
processing. Keep some of these things in mind both from an end-use
environment standpoint and from a storage standpoint. Do not store in
areas
where there are open containers of soaps, fluxes, etc., nearby.
From: Barbara Burcham [mailto:[log in to unmask]]
Sent: Thursday, June 02, 2011 9:22 AM
To: Stadem, Richard D.
Cc: TechNet E-Mail Forum
Subject: Re: [TN] Best Board Finish - beyond gold
Thanks everyone for you imput. What a great group of people!
Richard,
The application will be double sided, fine pitch array components, some
through hole components and going into a shock environment.
I will need to connect with the assemblers to check on flux and paste
compounds. Does this information help? You make an excellent point.
Must
have the total picture. I do not know, yet, how long boards will sit on
the
shelf before moving into assembly, either. I do know that shelf life
will
also impact this decision.
I do not think that I want to use tin...that hairy growth stuff.
Barbara
On Thu, Jun 2, 2011 at 8:01 AM, Stadem, Richard D.
<[log in to unmask]<
mailto:[log in to unmask]>> wrote:
Barbara,
What is the application, board type, component types, etc?
Immersion silver is my personal favorite, but that is completely
irrelevant.
You should choose a board finish dependent upon the application of the
CCA,
whether it has fine-pitch array components, including CSPs, whether it
is
double-sided with PTH parts or hand-soldered components, the environment
the
CCA will be used in, the flux type to be used, the alloy that is
required,
and several other factors that go into the decision.
Without complete knowledge of all these factors, it is hard for anyone
to
answer that question. I can tell you that IAg beats ENIG in cost, but
each
finish has strengths and weaknesses. Some definitely have more or less
than
others.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf
Of
Barbara Burcham
Sent: Wednesday, June 01, 2011 8:17 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [TN] Best Board Finish - beyond gold Hey Y'all, I am looking
for a
reliable bare board finish that beats the cost of gold.
What experience is out there?
What would you recommend?
Thanks,
Barbara Burcham
pcb Trace Design
[log in to unmask]<mailto:[log in to unmask]>
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