Carey,

We have produced quite a few multilayer boards with many 
combinations of different dielectric materials.  In most cases, 
you should not expect UL certification of the finished circuit 
board even if the raw materials are both UL rated.  With RO4003 
you will not get certified boards from any supplier because the 
material is not only missing a UL rating, but will burn if you put 
a match to it.  RO4350 is basically RO4003 with a flame retardant 
filler.  The electrical difference is that RO4350 has a 
dissipation factor is .004 instead of .002 with RO4003.

When you are mixing dielectric materials in general you should be 
concerned with the following with regard to the stackup:

1.  The first thing that should cause you concern is will the 
materials bond together.  RO4350 can be bonded with FR4 prepreg to 
anything else that will stick to FR4 prepreg.  However some PTFE 
based laminates will not bond to many prepregs.  So you should 
consult your fabricator early in the design to ensure that the 
materials will hold together after lamination.

2.  The next concern is warp.  If the dielectric materials are not 
balanced about the Z-axis, the board will warp.  The only question 
left is: "How much will it warp?".  The warp will be dependent on 
differences in Tg and X-Y CTE of the different dielectric 
materials as well as other things.

3.  Then other factors should be considered like:  Can you 
supplier process the board through processes other than 
lamination.  ie: plating, drilling, soldermask, etc.

The largest cost component in a circuit board is the raw material 
(not including yield).  RO4000 series laminates cost more to the 
tune of 3-5 times that of difunctional FR4.  There is no RO4000 
series prepreg yet so every board will have a different dielectric 
for the prepreg.  On a 4 layer .062" multilayer the best stackup 
is:

RO4350 / FR4 / RO4350 - little - no warp

The price may be lower for a RO4350 / FR4 / FR4 board, but you 
will need to waive the 1% IPC warp specification and will have 
added costs in assembly trying to deal with a warped board.

If you have any other question feel free to call.

Darren Hitchcock
(503) 359-2658
[log in to unmask]


Carey Ritchey/KENT/COM/AUGAT <Carey_Ritchey/KENT/COM/AUGAT.AUG 
Wrote:
| 
| FROM too long. Original FROM is 'Carey 
| Ritchey/KENT/COM/AUGAT 
| <[log in to unmask]>'
| 
| ----------------------  Original Message Follows  
| ----------------------
| 
| Has anyone built a 4 layer mulitlayer PCB utilizing  
| Rogers RO4003/4350 materials for two layers and FR4 
| for the other 2 Questions :  what type of stack up 
| did you use  we are imagining  0.020 RO double side 
| material FR4 prepreg and 0.020 FR4 double side  for a 
| finished of aprox 0.062What happens to flammability 
| rating if you hybrid 94VO rated FR4 with non rated 
| RO4003Can we still expect UL approval if we utilize 
| FR4 and RO4350 which is 94VO ratedAlso what sort of 
| cost saving is to be expected by utilizing FR4 for 
| the non critical layers.

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