FR-4 LAMINATE CHARACTERIZATION / CONTROL Printed circuit boards are manufacture with FR-4 laminate, a combination of epoxy resin impregnated glass cloth. The bonding agent used to join layers in a multi layer construction package is called prepreg, glass cloth impregnated with dry semi polymerized epoxy resin. The application of heat and pressure at the lamination process unifies the package into a multi layer board. The printed circuit industry standard for epoxy laminate cure is Tg, the glass transition temperature of the epoxy resin. The cured laminate is heated through two thermal cycles and measured using either DSC or TMA techniques to determine the delta in Tg between the two cycles. If the delta is small (less than 4 degrees F), the material is deemed cured since no additional polymerization occurred. Tg analysis does not always indicate how the material will process through subsequent mechanical and chemical operations. I am looking for ways to improve and tighten process controls over the material aspect of the process, any comments or recommendations would be appreciated. 1. Are there alternate methods for determination of the state of cure for epoxy resins ? Anything from the scientific world ? Polymer scientists ? Resin suppliers ? 2. Is there a documented procedure to quantify "machine ability" of materials of this type ? How can machine ability be quantified ? How is it typically determined in other material types ? 3. Is there a method for quantifying "hardness / softness" of an epoxy laminate. 4. What elements within the resin or board manufacturing process will cause variations in the state of cure or machine ability ? How can they be controlled ? 5. Is there a documented procedure for incoming material inspection to quantify material dimensional stability other than IPC - TM- 650 2.4.39 ? I am familiar with scaled flow and gel testing, but is anyone aware of a method to quantify growth or shrinkage of laminate before the fact ? Can material stress be measured ? Tony King Elexsys International Inc. Nashua 603-886-0066 [log in to unmask]