Hi Kelly,
'Wet greetings' from your old home town of San Diego... :) The rain finally
stopped today... wow... what a storm!
Your comments are right on, and in addition, I just wanted to point out
there is another problem with specifying the material as just 'FR4'... You
could end up receiving any of a number of different variations of the
material and still classify it as 'FR4'... The less clarity you put in the
notes, the less criteria your QC inspector has to reject material that is
undesirable... What if the environment that this board must survive in is
160 DEG C?
Let's say the manufacturer reads the fab drawing note that says ".062
FR4"... He goes and pulls standard FR4 material off the self and makes the
100 board order and ships it... You get the boards and put the 110DegC Tg
FR4 material in your product and it fails in test because the material was
heated beyond the glass transition temperature it was designed to withstand
and expanded in the z-axis rapidly cracking all the barrels of the vias in
your board... You can't reject the lot of boards now, they were built to
your drawing... you just bought them. Now the vendor COULD HAVE shipped you
180DegC Tg FR4 material... and you would never have had the issue.
The value of properly defined notes on the fab drawing is great. It
protects your company... and it protects the manufacturer as well from
supplying you with material that will not perform to your needs. Then he
doesn't have to guess what you *really* mean by 'FR4'. This is a good
thing...
Best regards,
Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com
-----Original Message-----
From: Dack.Kelly [mailto:[log in to unmask]]
Sent: Wednesday, January 12, 2005 8:42 AM
To: [log in to unmask]
Subject: Re: [DC]
Greetings Gary,
With regards to quality problems, if everyone in the design and mfg and Q.C.
chain has done their job right, you shouldn't have to expect any.
Hopefully, this is the case.
If the fabrication drawing is calling for .062 FR4 copper clad and nothing
more, here are some issues to consider depending PERFORMANCE CONSTRAINTS of
the design:
(1) .062 CC commonly infers an off-the-shelf "stock" material which will be
processed into a two-sided design. If this is the case, go to (2) If not,
go to (A)
(2) "Copper Clad" might be a little vague if this design has any current
carrying constraints. If this design has no current carrying capacity req's
over 1amp, check to make sure that min trace width is >/= to ~.010 [.25]
Check to make sure that the copper clad is at least 1/2oz. It will be plated
up another ~1oz during processing. Go to (3)
(3) Coordinate a manufacturability review with your contract assembly
vendor. They will be an invaluable source of information. They will
require the raw data from the design - the design database. They will get
back to you with a detailed set of issues, if any. If there are issues,
cycle them back thru the EE. Make sure that the issues are addressed in the
source design database. Often, CM's offer to just fix the problem. If this
happens, it is sure to crop up again in another iteration of the design as
it is re-output from the source.
(A) If this is a multi-layer design, ".062thk FR4 Copper Clad" is way too
vague. If this design is impedance controlled, it will need to spec the
impedance along w/ a layer stackup. You need to get with EE and contract
mfr and get requirements spec'd on the fabrication drawing.
Just some thoughts I had time for this morning.. Hope this helps.
-- Kelly
Kelly Dack
PCB Dsnr
Reno, NV
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary
Bremer
Sent: Wednesday, January 12, 2005 7:18 AM
To: [log in to unmask]
Subject: [DC]
Hello Designer Council members
At the company I am working for is calling out matterial .062 thick FR4
green copperclad laminate for their bare board.
My question for the form:
When this design was done in the Northeast by the electrical engineer and
outsourced to a board assembly house as a turnkey component. What type of
quality problems can I expect to deal with durning final assembly and final
test? What long term (customer returns) problems may result from this? Do
the board fabracation houses on the east coast march to a different drummer
than the rest of the country? The electrical engineer does not want to
change the drawing to specify what laminate matterial he truly intends to
use. The last company I worked for also had this same type of problem. The
electrical engineer designs/releases and I have to fix his mistakes.
Gary Bremer
Senior Manufacturing Engineer
Company located in California
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