We began using gold over nickel PCBs on a trial basis over 2 years ago.
It was so successful that we now have all boards with mixed or all SMT
content made that way. We have always used no-clean fluxes. The finish
was available from our PCB supplier at no extra cost from previous HASL
finish.

Actual process spec is 3-5 microns nickel with 0.05-0.1 microns gold
over.

Benefits are:

* maximally flat finish which is vital for fine pitch SMT
* error free fiducial recognition on assembly machines
* good contrast between pasted and no-pasted lands which aids inspection
* long shelf-life


Nigel Burtt
Production Engineering Manager
D - European HQ
Email: [log in to unmask]
Tel: 01793 842132
Fax: 01793 842101

----Original Message-----
From: Paul Klasek [mailto:[log in to unmask]]
Sent: Tuesday, August 11, 1998 1:42 AM
To: [log in to unmask]
Subject: Re: [TN] Gold Immersion and planarity


Hi Matthew

Muddy waters all right ; don't paint them too rosy ; No Clean on gold is
tight window .
Matthew , myself being a great fan of NiAu versatility ;
I still wouldn't say it's wetability is "far superior than HASL's" .
However without dissecting it over measurability and applied methods and
standards ;
something must have prompted you (usually folks struggle on NC gold) ;
if you have that good supplier of immersion I'd appreciate if you'd let
me know ;
in the process of establishing periodic benchmark system for immersion
finish presently .

Thanks a lot Matthew

Paul Klasek
http://www.resmed.com

> ----------
> From:         Matthew Park[SMTP:[log in to unmask]]
> Sent:         Saturday, 8 August 1998 9:18
> To:   [log in to unmask]
> Subject:      Re: [TN] Gold Immersion and planarity
>
> Dhawan,
>
> So, you try to skip all research headaches and jump right into the
> muddy water.  Check Enthone and kester web sites.    They have
> many excellent technical articles written on the subject of OSP's
> - www.kester.com
> - www.enthone-omi.com
>
> Also check July 1997 & August 1998 editions of Printed Circuit
> Fabrication for OSP and electroless immersion gold/nickel
> articles.  If you don't have them, name your fax, I will try my best
> to
> fax them on Monday.
>
> If you plan to use no-clean in near future, I recommend
> immersioin gold/nickel finish coating.  This is a drop-in
> replacement for HASL boards.  You don't have to fiddle
> around with the existing process.  Wettibilty of gold is far superior
> than HASL and solder joint fillet formation is far better.
> One major solder appearance change from HASL is all solder
> joints are dull-looking.  Solder joint embrittlement due to too
> much gold content (usaully 3/5% more) are unfounded.
> Immersion gold/nickel provides consistent gold thickness of
> 1um.
>
> One problem you might encounter (depending upon who your
> board vendor is for immersion gold)  is gold fall-out around SMT
> pads.  This could cause shorts especially for QFP pads.  Gold
> fall-out (fine gold dusts) is usually caused by too much plating.
> The problem can easily fixed by fine-tuning gold plating process
> by the board vendor.
>
> OSP coated board provides the same or better flatness than
> gold.  But the manufacturing process requires some fiddlings
> and the handling of boards are more sensitive.  It provides a
> superior  solder joint shininess and less intermetalic and cold
> joints.  This is because there are no oxidized and contaminated
> solder from HASL.
>
> Some of issues you might tackle when using OSP coated
> boards:
>
> Watch out how many heat cycles a product go  thru, and boards
> should be assembled and completed within a limited time.
> Don't leave them out on the floor too long when they have to go
> thru next assembly and heat cycle.  I guess I am talking about a
> few days..  Non or de-wetting could be a problem if not
> processed within a given time.
>
> Cleaning of mis-printed board could cause non-wetting problem
> as well.  This tends to remove a fraction of OSP coating.  0.35um
> thickness is indeed thin.
>
> Solder filling of thru-hole in the wave is another issue.  It will
> never get filled fully the way HASL coating.  Usually solder wicks
> up to about 50% or 75% of hole.  This is acceptable under IPC
> 600  class 2 and 3.
>
> You also have to deal with exposed copper area.  I don't think it
> will be a quality issue.
>
> Training of assembly people for the proper handling of OSP is
> also important.
>
> More active flux (Water-soluble) works better with OSP, and there
> are no-clean flux formulated for OSP.  I tested one no clean flux
> type but the result isn't better than the one I am using.
>
> I guess I am telling OSP is not a drop-in replacement for HASL
>
> regards
> Matthew Park
> SMT Manufacturing Engineer
> NII-Norsat International Inc.
> Surrey, BC.
>
> sorry I can not help you with surface flatness.  I don't think there
> is any guideline for that.  But the pad surface level  should be
> within a twice thickness of  leaded pin for QFPs.
>
> >>> "Dhawan, Ashok" <[log in to unmask]> August
> 7, 1998  1:48 pm >>>
> For fine pitch devices 15.7 mils and small chips 0603 ,do we
> have any
> IPC standard stating that what kind of surface leveliing /planarity
> required for placement of FPDs and 0603/0402 chips.Even
> accurate
> placement can go offline once the surface is not flat. the situation
> is
> worse when we are trying to place 0603 components on glue
> dots.
>
>
> Also, there are no. of options for HAl alternatives . We are
> comparing
> gold immersion and OSPs.Our circuit boards are having fine
> pitch devices
> extendable to 12 mils QFPs and 50/60 mils BGAs and chips
> down to 0402
> package size.We also intend to implement No-Clean process in
> near
> future.  We have limited experience with Au immersion/Ni
> electroless
> and OSPs.
> What are  views of experts who had some point of time decided
> course of
> action. What you think we go for?We want to go for process
> where we do
> not have to modify /readjust our current process based on water
> soluble
> soldering. Pro and Cons?
>
> Not to mention that I consider technet as my vital tool for problem
> solving. I will appreciate comments on this asap as I am running
> out of
> time and our process meeting is scheduled on Monady morning.
>
> thanks
>
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