I was with you till you said RF. That threw me for a loss tangent to my current thought process. Stating you were an EE and talking epoxy, I'm adhering to the premise that you were referring to traditional FR4 materials. That being the case, if it is a simplistic design that will be obsolete in 3 years any IPC-4101/21/24/26/30/99/101/121/124 material fabricated into a printed board by a Supplier who can spell coupon and talk enthusiastically about Class 3 of IPC-6012 and IPC-2221 will work. If however failure is not an option and long term reliability is a must and a FR4 material is required, then traditional dicy-cured materials are out of the equation. You must choose IPC-4101/126 or /129. Require the Fabricator to make controlled impedance coupons and IST or HATS coupons and pass the established acceptance criteria prior to granting authorization to ship. Not all materials are created equal so calling out a slash sheet that it complies to does not guarantee success. Some Fabricators can successfully make good product out the same material that others can not. The best material in the world does not a process make, but the few materials we have qualified to IPC-4101/126 and /129 are almost bullet-proof, so as not to be concerned with the caliber of Fabricator you have chosen. Dewey -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Honsowetz, Eric Sent: Thursday, November 08, 2007 12:40 PM To: [log in to unmask] Subject: Re: [TN] Specifications for the Epoxy in Glass/Epoxy Boards I need to be able to specify the laminate materials well enough to allow the boards to be fabricated by multiple suppliers and achieve the same performance from each PCB suppler without specifying to the supplier the vendor of the laminate system. Looking at 4101 I am uncertain that the Specification Sheets provide the detail to facilitate this, though they may be a good start. So my question in one sense is regarding the mixture of the epoxy. Is it all the same epoxy (as a EE I'm not sure if epoxy is a particular organic component or a general class of organic compounds) and if laminate systems that meet the specification sheet come from different vendors will they have the same electrical and mechanical performance. (We manufacture RF circuits so this is an issue) eric -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /* Sent: Thursday, November 08, 2007 2:20 PM To: [log in to unmask] Subject: Re: [TN] Specifications for the Epoxy in Glass/Epoxy Boards Hi Eric, All specifications are specific-some are just more so than others, some are more adequate than others. What exactly do you REALLY want to know? 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