I agree, an excellent posting David, thank you. I wonder if any vendors are using other laminates besides E-glass. I've experiments with "structural" S-glass. The glass yields a stronger lamination with a tighter weave. What about Kevlar? I don't have numbers for these other laminates. Does anyone else on the list? --- mkp=20 -----Original Message----- From: Ken Cantrell [mailto:Ken.Cantrell@xxxxxxxxxxxxxxxx] Nice posting. -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of David Hoover Sent: Tuesday, November 25, 2003 9:46 PM Alex, (it's been awhile) (below is my $.02 from a fabricator) In the case of FR-4 we typically see a series of variables that gives us the PCB dielectric properties. For example: If we look at the 5 most common (E-Glass) fiberglass styles used in the U.S.: 1060, 1080, 2113, 2116, and 7628 These yield different thicknesses within the PCB. The 1060 yields the thinnest all the way up to the 7628 which is (one of ) the thickest. The Dk of the pure resin of FR-4 epoxy is ~3.6 and the pure (E-glass) fiberglass is ~6.6 (@ 1 MHz . That's all I've found on the raw materials so far). It's the resin to glass ratio that gives us the variance. We typically find: Prepreg Thickness Resin Er Style Percentage (@ 1 GHz) 1060 ~.002" 69 3.63 1080 ~.003" 62 3.80 2113 ~.004" 55 4.00 2116 ~.005" 52 4.08 7628 ~.007" 45 4.32 Those values above are used to manufacture the various FR-4 cores. Each is basically like a building block used to achieve various thicknesses. The thinner ones typically cost more than the thicker ones. Some PCB fab shops or OEMs have rules where they require the use of two plys minimum. A key note to bring up is that even though the 1060 has the lowest Er, it would not be a good idea to build an entire PCB out of that prepreg. The resin content is too high and the pressed PCB would flow resin all over the edges of the lamination templates onto the lamination press. The thinner material(s) also has the greatest amount of dimensional movement within the PCB. An entire PCB built of 1060 would cost alot and would experience large amounts of material shrinkage when pressed. For cost and dimensional movement reasons we minimize the amount of plies by choosing those different styles of prepreg to build the various dielectric thickness. (This allows the pad to hole ratio used today to be maintained) There is beginning to be a few more choices of fiberglass styles. Nelco has introduced the "SI" style fiberglass which has a Dk of 4.4. When used to make prepreg, it yields a substantially lower Er product. If you factor in lower Dk resin blends (like the "-13") you can achieve a fairly low Er material (when compared to standard FR-4). Hitachi and a few others have blends coming on line that have fairly low Er values. These are all thermoset materials. (Meaning they cure into a hard rigid state) The thermoplastic materials (like PTFE based) have Er's that get very low but sometimes are very difficult to build multilayer PCBs with. We should start seeing more and more folks starting to test their materials at various frequencies soon. This is driven by issues such what Stuart, Andy, and Tom are discussing. As far as manipulating resins properties to achieve less loss, I havn't encountered that yet. I have heard of R and D efforts by the laminate manufacturers working on this, but I have not heard of any production ready releases. Kind Regards, David Hoover Sr. Field Application Engineer Multilayer Technology, Inc. San Jose, Ca http://www.multek.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.org List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu