Dennis
As one from the build 'em side, I have my preferences, but really the people
you should be asking are those who will build the boards. They will have
preferences based on their equipment set, and their experiences.
Assuming a board where there are a couple of through-hole parts like
connectors, my preferences are (in order):
1) all on one side (SMT reflow --> Wave)
2) on both sides, but bottomside laid out for partial wave fixtures (SMT
reflow --> SMT reflow --> Wave)
3) double sided, where bottom side parts have to be wave solder attached
(SMT reflow --> SMT glue on --> Wave).
Obviously #1 will give you the best cycle time as you only have to do one
pass through the SMT line. So it should be less labour to build. #2 will
normally give a better process yield than #3, so you save a bit on rework.
Also to consider though is the testing of the board - will the "all on top"
solution give you access you need for incircuit testing? Design for
manufacture has to be a consideration but also keep in mind design for test.
Kudos for pondering and asking the questions! And have a good weekend!
regards,
Graham Collins
Process Engineer,
Litton Systems Canada, Atlantic Facility
(902) 873-2000 ext 6215
-----Original Message-----
From: Dennis Ward [mailto:[log in to unmask]]
Sent: Friday, March 17, 2000 7:54 AM
To: [log in to unmask]
Subject: [TN] One side vs Both side
Good morning everyone,
Question for all you manufacturing gurus. Is there a
significant advantage, cost wise, to keeping all the components
on the top side of the board versus placing components
on both sides?
Now I do know that they are some NRE cost, but is it
significant? In the past I was taught you should try to
keep every thing on top. But it seems that high density
double side boards are very common. There doesn't
seem to be as much emphasize on consolidating all
the components on the top side.
As an example if you quoted two boards - all things
being equal except that one was populated on the
top and the second board was populated on both
sides what would be the cost difference (if any)?
The reason I ask is that I am laying out a board
that I may be able to squeeze everything on top.
However I'm tempted to just throw discretes on the
bottom of the board. The engineer asked what was
I going to do. I told him that I'd try to keep everything
on top. He then asked "why"? I answered it would be
easier to manufacture, inspect, debug, eliminate some
manufacturing steps and eliminate some cost. But I
started thinking and wondered if my thinking was backwards
and these concerns are negated with the advance of
technology.
Anyway, any advice would be greatly appreciated. Also
I would like to take a moment and thank everyone for
their particpation on this forum. It has proved extremely useful
for me personally. Enough so that a few strings of humor well
not affect my judgement as to the value of this forum. Actually
I enjoy hearing some of the "old timers" discuss the days of tape
and exact-o knives - personally never had the pleasure.
Thanks
Dennis Ward
Net to Net Technologies, Inc.
603 427-0600
[log in to unmask]
http://www.nettonettech.com
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