That's sort of ironic...I mean, on the face of it, I'd be a lot more
concerned about a board with 2000 5 mil spots of exposed copper, than one
with completely bare copper!

Timothy Reeves
QA Manager/Process Engineer
ECD Circuit Board Division
13626 S. Freeman Road
Mulino, OR 97042
(800) 228-8198    Fax (503) 829-5482


|-----Original Message-----
|From: Hill, Mike E. [mailto:[log in to unmask]]
|Sent: Tuesday, September 05, 2000 9:31 AM
|To: [log in to unmask]
|Subject: Re: [IPC-600-6012] FW: Exposed copper
|
|
|All,
|
|I did not help write para 3.5.4.6 in 6012 but I assume the
|"percent" would
|be interpreted the same as we did measling by classes a few
|years ago.  For
|example:
|
|The total board area is the basis for the percentage.  To
|follow the example
|started by Mark below the 5 square inch board for Class III
|would allow .05
|square inches of exposed copper (1% of 5 sq. inches).  For
|exposed copper
|spots that average 5 mils by 5 mils (.005 in X.005 in  = .000025 square
|inches per spot) you could have 2,000 (counting both sides)
|such spots (.05
|sq. inches/ .000025 sq. inches per spot)  per board.
|
|Note:  To be conservative I would always use the largest
|dimension of the
|spot and square it in this calculation.
|
||>
|>
|> -----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

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