Just a little delayed feedback on the subject...

I don't understand how a single orientation of PWB's in the array helps
during reflow. Wave, OK, but reflow? How do you know you've got them all
right vs. all wrong? I can't think of a board I've done where all instances
of all packages are in the same orientation on a given board anyway. so
even if all boards are the same in the array (which is still by far the
most common case), some parts will be in both a horizontal and a vertical
orientation. I'd think variation in location within the oven would matter
more than orientation, and you've always got that to deal with.

For what it's worth, we number each PWB in the array. So if something
starts popping up, like a cold solder joint, cracked cap, or whatnot, if it
always carries the same placemark #, it's very helpful in finding the root
cause.

As far as letting the CEM or boardshop do the array... don't I wish. We
don't necessarily stay with one boardshop or CEM through life-of-product,
and sometimes use more than one of each at any given time. So... we need to
control it if only for the sake of consistency. Also, we need to know and
approve EXACTLY how the boards are being singulated. If we don't control
the array, we can't control that.

Another FWIW: Sometimes you can simplify the singulation and/or conformal
coat by complicating the array.

It's not rocket surgery and we do try real hard to solicit and review input
from whoever we're dealing with at the moment.

As Jack said, the CEM doesn't have any big incentive to save YOU money.
Their aim is to save THEM money. You need to be sure it isn't going to COST
you money when they tell you what they'd like to change. If you at least do
a concept first, you ought to have a pretty good idea of what your
individual bareboard cost should be and you can keep them honest.

I say start with the best price for the things you can control. If they can
show you a lower overall cost with a higher per PCB price, jump all over
it.

-Chris

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------