Hi Doug! OSP is a wonderful surface finish in many situations but there are
some use applications where the other finish alternatives have an
advantage:
1) Field repair - OSPs don't provide the long term solderability on pwa's
which have been in the field for a number of years which sometimes are
subjected to upgrades/changes. It is typically an uphill struggle to have
good solderability for HASL for servicing an assembly which has been in the
field for 5-10 years anyway and OSPs just give up the ghost way to early in
comparison to metallic surface finishes.
2) Multiple thermal excursion processes - it is not uncommon on some
complicated assemblies to have 2 reflow excursions (top/bottom), an odd
form component attach excursion, an adhesive cure excursion, and possibly a
repair excursion. Add in a couple of cleaning steps and you really push an
OSP to the limit.
OSPs have a definite place in electronics assembly - I just look at them
as one "tool" in our toolbox of surface finishes for the different
soldering processes used in the industry. We use OSPs at Rockwell Collins
but in very specific applications/designs. We are also using Immersion
silver, Immersion tin, and ENIG very successfully as well.
Dave Hillman
Rockwell Collins
[log in to unmask]
Dougal Stewart <[log in to unmask]>@ipc.org> on 04/18/2002
04:56:52 AM
Please respond to Dougal Stewart <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: Re: [TN] Immersion Silver
I would like to know why people don't use OSP - from a board shop's
viewpoint, it is the best finish to put on a board - why ? because it is
very simple chemistry, puts no thermal shock on the product, is applied on
a
SHORT conveyor line, and can be easily reworked unlike ANY of the other
finishes. The assembly guys don't like it if they start assembling a
product
and then stop because they don't have the parts to finish the job, but
anyone that puts a board into assembly without the ability to finish it
within 6 hours obviously knows nothing about world class manufacturing
practise. As for shelf life, if your stock is even 2 years old, send the
boards back to the board shop and for a small fee they just put them back
down the line again and you have a finish that is good as new, without
having undergone a vicious chemical attack to remove the finish.
Just my thoughts !
Dougal Stewart
email: [log in to unmask]
phone: +44 1896 822204
mob: +44 7984 629667
----- Original Message -----
From: "Jack C. Olson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 17, 2002 4:22 PM
Subject: Re: [TN] Immersion Silver
> Hmmm,
>
> Well, at some point in EVERY new technology it was used by less
> than 3% of the world, eh? Guess I'm just a trailblazer....
>
> naw, just kiddin ya.
> I subscribed to a magazine called Circuitree, and the last issue
> came bundled with another publication called "The Board Authority"
> which has some very well written (and well researched!) articles
> on alternate finishes. I can't see any downside to using silver
> in our applications, and I've looked all through the archives for
> Technet, DesignerCouncil and PCDlist forums, still no show-stoppers,
> so we tried it for the first time on our last design. Yes, HASL and
> NiGold do work fine, but maybe we can get the same functionality
> for cheaper, and do our fab vendor a favor in the process, since
> they seem to prefer it (less steps? more reliable? not sure) maybe
> the fab guys can answer that one....
>
> Jack
>
>
>
>
>
> "WEEKES, MICHAEL HS-SNS" <[log in to unmask]>
> 17Apr2002 09:16 AM
>
>
> To: "'TechNet E-Mail Forum.'" <[log in to unmask]>
> "'Jack C. Olson'" <[log in to unmask]>
> cc:
>
> Subject: RE: [TN] Immersion Silver
> Retain Until: 05/17/2002 Retention Category: G90 - Information and
Reports
> Caterpillar Confidential: Green
>
>
> There must be some reason why less than 3% of the world has moved toward
> immersion silver. Why doesn't HASL or NiGold work for your application?
>
> Mike
>
> -----Original Message-----
> From: Jack C. Olson [mailto:[log in to unmask]]
> Sent: Wednesday, April 17, 2002 7:39 AM
> To: [log in to unmask]
> Subject: Re: [TN] Immersion Silver
>
>
> The PCD magazine list went down before I could get an
> answer to this question, does anyone have experience
> with silver and contact switches?
>
> ==============================================
>
> Most sources say a silver surface will not be solderable
> after a month or so unprotected. (Even in a baggie it will
> be okay a year later?)
> Anyway, you say it is good for switches, which would solve
> some of our hard gold plating problems.
>
> But I would think the "unsolderability" of the aged silver
> surface (unprotected in the unit and tarnished?) would
> affect the reliability of the switches, wouldn't it?
>
> Jack
>
>
>
>
>
>
> Rob Mongey <[log in to unmask]>@freelists.org
> 4Apr2002 06:08 AM
>
> Please respond to [log in to unmask]
>
> Sent by: [log in to unmask]
>
>
>
> To: [log in to unmask]
> cc:
>
> Subject: [pcdlist] Re: Immersion Silver
> Retain Until: 05/04/2002 Retention Category: G90 - Information and
Reports
> Caterpillar Confidential: Green
>
>
>
> Hi all,
> Good to see Immersion Silver is starting to take off. We've been
using
> it
> in here for about two years, and it is now our prefered board finish (We
> get silver finish unless we specify differently.) More common useage will
> mean that maybe more Far Eastern shops will start supplying it.
>
> We started to use Silver because it is so adaptable to what we need
> our
> PCB surface finish to do, namely:
>
> 1. Good solderability. (Silver excels at this, ask any vendor).
> 2. Flatness for fine pitch SMT. (Silver is as flat, if not flatter than
> Gold)
> 3. Mechanical strength for carbon pill switch contacts / Elastomer
> contacts. ( Flash Gold is weak, and hard Gold gives SMT solderability
> problems)
> 4. Stability for compression power contacts. (We have power contacts on
our
> PCBs that mate to battery contacts via a spring compression. We found
that
> the nickel under gold can cause problems with electrochemical migration
> toward our battery contact.)
>
> Immersion silver is the most suitable choice that can do all four. I'd
use
> gold as an alternative, but we'd have to compromise our designs somewhat.
>
> We specify our Silver finish as 0.1 Microns Min to 0.2 Microns Max, over
> bare copper. Anyone else do it differently? Or do we trust our board
shops?
> :)
>
> Regards,
> Rob Mongey.
> CAD Technician.
>
> Robert Mongey <[log in to unmask]> Tel : +353 (0)91 774300
> Bio Medical Research Direct : +353 (0)91 774338
> BMR House, Fax : +353 (0)91 774302
> Parkmore Business Park West, Mobile : +353 (0)87 2485262
> Galway
> Rep of Ireland.
>
>
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