[SI-LIST] Re: PCB thin dielectrics

Hi Ivor,
such thin dielectrics are mostly used for power/ground plane pairs and 
possibly for low-speed (thus not impedance controlled) signal layers. They 
aren't as good for controlled-impedance signal layers because the trace 
widths necessary to achieve e.g. 50 Ohm characteristic impedance become 
impractically narrow, which results in very poor impedance control and 
high skin loss. For power/gnd pairs though they are great since they 
greatly cut down the supply inductance and add embedded capacitance (the 
former effect is the more important one). As you already noticed a nice 
side effect is they reduce the overall board thicknedd (or allow you to 
double-up high-current supply planes for even lower inductance while 
keeping the board thickness constant).

As for reliability, I have used down to 2 mil thick dielectrics without 
any issues, and availability and cost of such materials is pretty good. 
Below that thickness you need to be careful with regards to reliability 
etc., either work very closely with the vendor and/or do a good amount of 
reliability and stress testing. Experienced PCB design & manfuacturing 
people tell me that 1 mil is still achievable, 0.5 mil is stretching it, 
but I must admit I do not have personal experience with such thin layers.

Just my 2 cents of course, I'm sure other will chime in with more details.

Wolfgang







"Bowden, Ivor" <ibowden@xxxxxxxxxxxxxxxxx> 
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[SI-LIST] PCB thin dielectrics






Hi SI people,
 

Could I get some comments on the use of "thin" (<0.0035") dielectrics in 
PCBs, in terms of available materials, cost, reliability, dielectric 
strength, trace width vs dielectric constant, power plane capacitance, 
stories, studies, useful web links, any other pertinent issues? Base 
question is, could this be a practical way to increase PCB layer count 
while maintaining overall PCB thickness?

 

Any / all information / comments welcome.

 

Thanks,

 

Ivor Bowden

 


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