Be careful in price comparisons when concerning OSP's.  Unlike metallic 
finishes, its price is frequently figured for board surface square feet(6' 
for 18"x24")due to relatively high dragout losses, not finished square 
feet(in most cases, <3').

There are definite benefits in processing for the board shop. It is 
possible, not recommended, to re-work the product forever, or until you 
(10's of microinchs a time) etch your copper below spec.

Additionally, since it is recommended as the final step prior to bagging, 
images are processed as images, not panels of 4 of more(for other methods). 
With every extra image per panel, handling at the board shop will increase, 
causing non-material operating costs to increase.

Once ALL costs are figured, OSP's could be equal to (or better than) HASL 
dollarwise(depending on product). They do seem better environmentally and 
have much better planarity than HASL, but I do not think it will warrant 
cost reduction until it replaces HASL as a board shop's primary 
solderability preservative.

Charles Stuber
Chemical Process Engineer
Automata
703-450-2600
[log in to unmask]
http://www.automata.com

 ----------

From: TechNet-request
To: rbormann
Cc: TECHNET
Subject: cost of OSP vs HASL PWB coating
Date: Monday, September 11, 1995 5:55PM

you said in your CircuitWorld Sept 95 newsletter:

>Fabrication Costs ... estimated HASL costs $ .75 - 1.00 per square foot
>                      estimated OSP costs $ .35 per square foot
>The costs to the PWB fabricator are significantly reduced and the assembler
>benefits from increased yields and better product reliabilty.

At the recent Surface Mount International Conference, a paper was presented
by Ray, Artaki, Wenger, and Machusak of AT&T Bell Labs. They offered the
following fab cost comparisons ($/sq. ft.)

        Imidazole  immersion tin   HASL   Pd/Cu    Pd/Ni   Au/Ni
min     .020         .75           1.40    1.40     2.30    2.80
max     .050        1.10           2.40    2.40     3.70    4.00

These numbers are actually my interpretation of the graph shown in the
paper as published in the proceedings.

These figures are a little higher than what your Newsletter showed.

I would interperet that for a typical 3 sq ft panel, the cost savings to
the fabricator might be 1.90 to 1.20 per sq ft switching from HASL to OSP.
If that is the case, a 4 unit per panel might cost the fab supplier say
$0.40 less to produce.

If I knew I could save $0.50 per unit on buying PWB's (as a PWB assembler),
I would be a hero. To date, no supplier of our Company is offering such
price reductions. Maybe they will soon, let's hope.

Based on early testing we have done of these coatings, I am ready to change
when the savings justifies the relatively minor process changes, but
probably not until that time.

Jerry Cupples
Interphase Corporation
Dallas, TX