We are experiencing some bow and twist, greater than 1%, on standard 4 layer
multilayer.
I know that the copper tracks and ground plane is spread quite evenly over
the circuit.  Iam also testing a different build from our existing one.
Details as follows:

Existing Build                                    Testing Build
!/2 oz Outer Foil                                !/2 oz Outer Foil
1 x 2125 pre-preg                            1 x 2125
2 x 7628                                            1 x 2125
0.51mm 1/1 Core                             0.93mm 1/1 Core
(Core Tg >125)                                (Core Tg >140)
2 x 7628                                            1 x 2125
1 x 2125                                            1 x 2125

Gel time is short flow:  120 seconds +/- 20
Vacuum press cycle details:  90 mins @ 175 deg C  /  Heat up rate 6 deg C
per min  /  36 min cool down @ 10 tonnes.

I would also be interested in comments on the way panels are thermally cured
at final cure photoimage - racks, Tunnel dry, etc ??

Ian Paterson
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