Also, you will want to make sure that the coupons are placed away from any
areas where board fabricators will be using tooling. We have gotten poor
microsections from test coupons with that used as a justification.
Subsequent microsectioning of other areas of the panel verified that
assessment.
-Stve
Steven K. Lustig
Process Engineer
EMS Technologies, Inc.
Norcross, GA
(770) 263-9200 x4714
[log in to unmask]
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Wednesday, October 13, 1999 8:02 PM
To: [log in to unmask]
Subject: Re: [TN] Specifying test coupons
In a message dated 10/13/99 6:30:39 PM Central Daylight Time,
[log in to unmask] writes:
> few of my personal preferences regarding test coupons:
> (1) place the test coupons on center and the four corners of the pannel
(top
> two corners of the pannel normally have less plating due to field
> distorsion, insufficient stir and "dead corner of the plating tank").
Check
> for uniformaty.
> (2) all the surface finishing shall be well showcased on the test coupon,
> e.g. wire bonding pad (soft Au), ZIF edge (hard Au), HASL or OSP, etc.
> (3) the feature of the test coupon should be the finest of the
circuitary,
> sufficient for SIR testing (with the solder mask).
> (4) there should be an area (0.5 x 1.0 cm) with minimum cupper layer for
use
> as weight loss test (outgas test).
> (5) coupon shall have wire bonding pads and die attach pads for wire
bonding
> test...(if you have enough Au on the coupon, you will be fine for the PWB
> for wire bond..see item (1)...
> (6) PTH and vias of the smallest feature of the design...including via
plug,
> if it is required.
> (7) all the other goodies IPC and Mil wants (representing the designed
> c.c.t, etc. etc.)
> Warning: such "fussy" only worked with some vendor who willing to improve
> the process and understand the needs to go through the "hell"...I have
> someone roll his eye balls to almost completely "white"...also some sales
> and purchesing guys say: "how much you will pay?" and some shake their
> heads to the stage I start to worry about to pay some HMO fees...However,
> who ever did it with design and qualification hardly have any problems
> during the production...
> If you are going to use the "fussy" methods, be ready to face some "life
or
> death" threat.
> jk
Joyce,
Your recommendations are right on! (boy, you are smart!) Because it truely
does specify the means that requirements for the particular board are met.
In my past case recently (the internal shorting deal, fractures within the
laminate) were not evidenced with the standard IPC test coupon requirement.
Earl also alluded to it in his responses, the test coupon should be
REPRESENTATIVE of ALL the circuitry and holes that are used in the
particular
board! It's not that difficult to do, but it does provide a "comfort factor"
that if the test coupon looks good, you can sleep at night because you know
the boards are probably good too.
There are so many variables within the way things are done depending on the
design (the angle of the cutting flutes for different hole diameters and the
drilling problems with polyimide as an example) that unless one has a
representative test coupon of the actual board, there will be things that
definately can be missed and wind-up biting you in the butt later...we still
have some pain in the ol' buttocks from that one.
If the fab vendors don't want to work with you on that, in my opinion they
got something to hide...or might be unsure about their processes.
-Steve Gregory-
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