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Date: | Mon, 04 Dec 95 10:38:21 EST |
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Dennis,
If the base laminate is made of a high Tg laminate then the
"Z" expansion (PPM) is less likely to exhibit the type of failures
as you mentioned. High Tg laminates are more favorable for products
that have multiple thermal excursions. (i.e., two or three assembly
thermal excursions like wave, IR, FTIR, Hot Bar or forced air) Another
thing that that is critical is the elongation and tensile strength of
the plated copper in the hole. Of course ample (correct) copper
plating thickness is essential. High Aspect Ratio plating has a
tendency to produce a "dog boning" appearance that could have a less
than desired thickness in the center and too much at the knees. These
types of deposits each will have polar extremes as far as E and T
results. A good (level) and evenly plated (distributed) PTH will have
more consistent results and can easily then have variable copper
plated thru hole thickness' tested to find what thickness will produce
none of what you mentioned.
You can pre-bake parts to remove and potential moisture that could
increase your "Z" expansion prior to thermal activity.
Some tests have indicated that a PTH >1.5 mils reduces PTH anomalies
but at >2.0 mils they come back. Other old timers swear that a panel
pattern copper plate combo will help with this kind of problem.
(??????I dunno...never tried it!)
Another important thing that requires attention is to preheat parts
prior to extreme thermal activity. (e.g., IR preheat prior to fuse
also
slow cool ramp as to not thermally shock parts)
Good luck.
DHH (Groovy)
______________________________ Reply Separator _________________________________
Subject: High Z Axis Expansion Board Materials
Author: [log in to unmask] at SMTPLINK-HADCO
Date: 12/2/95 5:27 PM
We receive questions about plating high Z axis expansion board materials.
When the expansion from assembly soldering is too great, surface pads around
the holes lift, or the plated barrel cracks. Does anyone have a standard
practice to prevent these phenomena when using laminate with great amounts of
Z axis expansion (we think more than 6%)?
Thicker plating in the hole?
Alternate metals plated?
Dennis Fritz
MacDermid, Inc.
245 Freight Street
Waterbury CT 06702
Phone 203-575-5740
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