Sefika
In general, fabricators can build boards with mixed materials and laminate thicknesses. There are some consequences. UL recognition can be difficult or nearly impossible on some combinations. Different thermal properties of different materials can in the best case lead to warpage of the finished boards. In the worst case, you could have PTH reliability issues.
There are also some compatibility issues in selecting materials for mixed dielectrics. The main one is making sure the materials have compatible press cycles. For example, a prepreg with an aggressive (high temp and/or long time) lamination cycle might not match up with an FR4 laminate that isn't designed to take that kind of thermal processing.
Tolerancing is typically done by specifying the most important layers/materials and an overall board thickness. You'll need one "as required" opening to allow for adjustment of overall thickness.
For impedance modelling, I recommend a field solver which can deal with complexity of mixed dielectrics.
You will most definitely want to work very closely with your board fabricator in designing a mixed dielectric board. Merix has an extensive background in mixed dielectric board fabrication. Feel free to contact me off-line if you'd like more information.
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From: Sefika Ozkal[SMTP:[log in to unmask]]
Reply To: TechNet E-Mail Forum.;Sefika Ozkal
Sent: Monday, October 07, 2002 9:48 PM
To: [log in to unmask]
Subject: [TN] Laminate Materials
Hi,
I am searching high performance laminates, prepregs and adhesives. I have found some laminates - FR4/406/408, Arlon33n/35n/85n...,Speedboard, N4000/6000..., RO3003/3006/3010...- with their specifications, I want to get much more information about laminates such as:
-Can I design a PCB with different laminates for each or some layers?
-Can I design a PCB with different laminate thickness for each or some layers?
-If they can be done, how can the tolerans be determined?
-If they can be done, how can we calculate the impedance?
Moreover, I need addresses of PCB manufacturing companies for high speed/high frequency design.
I am waiting your responce.
Thank you,
Sefika Ozkal
Electronics Engineer
ASELSAN Inc.
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