Colleagues,

We have occasional boards (just a few from a batch of 200 or more) warp
quite badly following reflow. The boards concerned are about 270mm x290mm
(10.5" x 11.4")

Is there any logical explanation why this happens? The boards are supplied
flat, so it would appear there is a built in stress factor which gets
relieved when the board is heated or there is some unequal
expansion/contraction occuring across the layers. Can this be down to a
mixed warp and weft of the glass in the outers during the layer build?

> Thanks,
>
> Nigel Burtt
> Production Engineering Manager
> Dolby Laboratories Inc - European HQ
> Email: [log in to unmask]
> Tel:     +44 (0)1793 842132 [direct line with voicemail]
> Fax:    +44 (0)1793 842101
>
>

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