Greetings all,
We have an urgent request from a 6012 user.  Product is being held up for
shipment.

The email below and attached photo is a request for interpretation
concerning a manner of exposed copper.  Does anyone recall the original
thinking behind the 3.5.4.6 on how to property apply the percentage of
conductor surface.  My notes show no prior discussion on this paragraph.
See the question below in the original email.

I believe the cause resulted from a combination of selective tin strip and
solder mask clearance.   A small portion of the conductor is exposed with
bare copper.  Touchup would be cost prohibitive.  Does the specified
paragraph best cover this issue?  Anyone crossed this bridge before?

" 3.5.4.6 Final Finish Coverage Final finish shall meet the solderability
requirements of J-STD-003. Exposed copper on areas not to be soldered is
permitted on 1% of the conductor surfaces for Class 3 and 5% of the surfaces
for Class 1 and Class 2. Coverage does not apply to vertical conductor
edges. "

The bottom line is: "is this an acceptable condition"??????

Please reply to "all" to capture the discussion.

Thanks, hope everyone will be able to make Miami next week.


        C. D. (Don) Dupriest
        Lockheed Martin Missiles and Fire Control - Dallas
        Electronics Manufacturing Engineering
        Mgr. - PWB Process Development
        Ph. 972/603-7724 fax: 972/603-3548
        Email: [log in to unmask] <mailto:[log in to unmask]>


----------
From:  Cirtech [SMTP:[log in to unmask]]
<mailto:[SMTP:[log in to unmask]]>
Sent:  Friday, September 01, 2000 12:13 PM
To:  [log in to unmask] <mailto:[log in to unmask]>
Subject:  FW: Exposed copper




-----Original Message-----
From:   Mark Alexander
Sent:   Friday, September 01, 2000 8:30 AM
To:     'Don Dupriest'
Subject:        Exposed copper

Don,
I've attached a picture of an area that is typical of an exposed copper
area. This is The trace that leads into a SMT pad that is not covered by
soldermask. The actual dimension of exposed copper is approx. .003 to .005
mils. According to ipc-6012 section 3.5.4.6 there is an allowable amount of
exposed copper of 1% or 5% depending on what class the board is called for.
My question is, how do you calculate this. How do you translate 1% or 5% of
conductor surfaces. Is it total square inches of copper on board multiplied
by 1% or 5%? If so then the formula for a board with a total of 5 square
inches multiplied by 1% = .050". What then do you do with the .050'.? If it
was 5% then = .250'. What do you do with that?
Please fill me in
Thanks,
Mark Alexander
Engineering Mgr.
Cirtech Inc.
Orange, Ca.
714-921-0860 ext. 220
 <<copper.bmp>>