Bob,

Were the panels cooled below 120C (250F) before contacting water in the
cleaning process. If the panels are still around the Tg the distortion
can be considerable. Maybe rotating the panels gave them a bit more time
to cool down.

We had similar problems but they were solved by adding a cooling
conveyor section with fans before the water rinse.

Regards
Paul Gould
Teknacron Circuits Ltd

In message R_R_HOLMES writes
>The question has to do with a deformation of rigid material in the HASL 
>operation. 
>
>I have seen the phenomena you describe.  In our case the cause was the HASL 
>operation itself not the material.  Apparently the transport system in our 
>horizontal HASL applied uneven forces to the panel and literally bent it. This
>was an in-plane deformation, not an out-of-plane warp.  The deformation looked
>as if the hot panel were pulled by its edges, and/or restrained along its 
>center line.  The result was a deflection of 20 mils or more of features at 
>the center of the trailing/leading edges with respect to features at the 
>outside of those edges.  The best proof of this model was the observation that
>the deflection could be removed by heating the panel above glass transition 
>temperature and cooling uniformly in a stress free state.  This problem 
>occured with DSR not MLB and was most severe for designs where the surface Cu 
>features provided no resistance to the deformation.  Apparently the internal 
>Cu planes reenforce an MLB. The quick solution was to rotate the panels on the
>conveyor.  I believe that we were later able to improve the conveyor and 
>eliminate the problem. 
>
>Bob Holmes  PhD 804-226-5114 [log in to unmask] Viasystems Technologies 
>(formerly Lucent) 
>

>------------- Begin Original Message ------------- 
>From: ipc.ipc.org!TechNet-request 
>Date: Fri Jan 31 11:04:08 -0600 1997 
>Subject: Rigid Laminate stabilty 
>
>I have been experiencing some unusual material movement recently on .059 FR-4.
>A distortion in some cases in excess of .020" over 24 in. has been 
>experienced. It manifests itself after hot air level and is commonly detected 
>at legend or fabrication when the tooling holes no longer fit the pins. 
>
>We have evaluated all of our internal processes to insure we are not inducing 
>any excessive stress. The highest temperature exposure is 490 deg. F during 
>H.A.L. . We have found that pre-baking the material does control the problem. 
>Detailed analysis indicated that the material is in fact completely cured from
>the manufacturer. 
>
>My concern is that although this is a random occurrence, I have established a 
>notable increase in frequency on non pre-baked ridged material. Although more 
>prevalent from one supplier, since we have been checking I have also seen an 
>increase in other suppliers as well. 
>
>Is anyone else experiencing this concern? 
>
>Ed Cosper [log in to unmask]
>

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