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And how if the material is being press. Because in fab, they're going to press the material right to get the desired thickness. Is it gonna change the dielectric also?
And how if the material is being press. Because in fab, they're going to press the material right to get the desired thickness. Is it gonna change the dielectric also?
well, i am also curious whether the dielectric thickness will change when they press the dielectric during fab...
this is because changing in dielectric thickness can japordise impedance matching of a trace... (therefore... trace is not properly matched... can effect the frequency of signals intended to be transmitted through the trace)
when signals travels through an unmatched trace not proportional to its speed; the signal will suffer loss and quality of the signal will be japordised.
but judging from my previous pcb fabricators; usually... pressing the material does not effect the dielectric thickness much... (dielectric constant of course does not change)
however, i am not sure if your board design is uptill 24 layers, whether the dielectric thickness will be effected....
this is just my observation ; i am not a pcb designer.. i just design high speed boards uptill 6 layers for design verification....
And how if the material is being press. Because in fab, they're going to press the material right to get the desired thickness. Is it gonna change the dielectric also?
The press is quite constant. What differs is the resin content for various sizes of material. For example look at differences between different prepregs in the following pictures. Imagine a sandwitch using those in different combinations.
The resin content will be heavily different.
You should pay attention to the 'real' stackup of your PCB, and especially the resin content.
Most of the time, the specification are given for 'pure' material.
When the PrePreg is fabricated, there is some resin is added to glue the fibrous laminate. The resin has a different dielectric constant, and the actual dielectric constant vary, depending on the resin content.
You have to call your PCB manufacturer to have the actual values...
In fact, there is a dielectric constant for each laminate thickness for a given material.
Here is a datasheet of High Tg PCB material from isola.
You could see that the impact of the resin content of the dielectric is more important than the frequency....
I 'm not designing critical High speed PCB, but I have heard that for small series, the manufacturer buy a stock, make measure, and then adapt the design to the characteristics of the stocked material...
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