1
Web the ground, Alain, if it's solid (the CTE's of copper and mask fighting
without grab simply slip = blister).
or at least dot the ground , to get some mask adhesion back to laminate .
Basically the ground is too a large area (even teflon gives up eventually on
fry pans)
You can ease the pain a fraction by more even ramp up of preheat = giving
enough time to mask to transfer the heat to copper; thus keeping some
balance in unmatched neighbors .
2
Often when speeding-up (deadlines) curing the top layer is dry and wet on
copper blisters afterwards .
3
Contamination is usually the last problem (still common enough)

cu         pk


-----Original Message-----
From: Alain Mathieu [mailto:[log in to unmask]]
Sent: Thursday, 16 December 1999 8:21
To: [log in to unmask]
Subject: [TN] Soldermask peeling and blistering



Hi TechNetters.

We are a OEM that manufactures Hi-frequency products  ( 5Mhz to 1Ghz range)
and therefore we use pcb (bare board) with big ground planes on both sides.

all our boards are FR-4  with solderMask over bare copper.

When we go thru the wave soldering process we experiment blistering and
peeling offon the ground plane.

We use Alpha No-Clean 26F flux ,  preheat top side at 230oF-240oF, bottom
side 300-320oF and a dwell time of 2.4-2.6 sec.
Solder Bath temp is 480oF.

In the past the pcb mfr was using a different Soldermask  but now he uses 2
brands with approximately the same results :  Epic #200 and Entone #3242.
The pcb Mfr was suspecting a problem with the curing, the thickness or a
contamination before soldermask application that could explain

Is there any one who had the same or similar problem?  Any help on how to
resolve this would be greatly appreciated.

Alain Mathieu
Electroline Equipment Inc.
[log in to unmask]


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