Hi Mike, Most of the laminate manufacturers have what is called as Standard, low resin & high resin prepregs or B-Stage, they could also formulate to a particular resin content type if you are a strategic customer & buy the minimum prepreg quantity that comes in a roll which could be a few thousand sheets. The basic reason why anyone would use the different resin content prepregs would be to meet the dielectric thickness, impedance & overall thickness requirements per the customers spec. In certain designs where the copper thickness on the surface is thick or unevenly distributed you may need a resin rich prepreg to fill the spaces otherwise you may end up with laminate voids. Some customers may spec. this in their drawing based on design considerations or past experiences with concerns noticed with using standard material. There is also another factor one would like to consider is the type of FR-4 material that is being used with the different resin contents, whether ii is a low, medium or high flow prepreg as this would also have an effect on the final dielectric thickness one is targeting to achieve. Hope this helps. Krishnan SANMINA-SCI Quality Assurance / NPI Manager E-mail: [log in to unmask] Phone (Off): 082-363000 Ext. 1602 Mobile: 012-8888-379 -----Original Message----- From: Tom Bresnan [mailto:[log in to unmask]] Sent: Wednesday, May 19, 2004 5:16 AM To: [log in to unmask] Subject: Re: [TN] FW: [DC] Core Constructions Let me also add that lead-time may increase as well as cost. Be sure you absolutely 'need' the material. Most fab houses won't have it on the shelf (can't anticipate every customer's needs) and there may be minimum run costs incurred as well. Work with your board vendor(s) to come up with a standard material stackup to lessen the impacts. -----Original Message----- From: Jeffrey Bush [mailto:[log in to unmask]] Sent: Tuesday, May 18, 2004 4:17 PM To: [log in to unmask] Subject: Re: [TN] FW: [DC] Core Constructions You are able to get higher resin contents from most laminate suppliers. They will have a part listing of standard glass styles with varying resin contents. Increasing the resin content in usually done to solve an issue like poor wet-out of the glass, or voiding due to thicker copper. Generally thickness yield per ply will increase with the RC, as will the cost. Jeffrey Bush Director, Quality Assurance and Technical Support 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302-1890 Tel. 802.257.4571.21 Fax. 802.257.0011 [log in to unmask] http://www.vtcircuits.com -----Original Message----- From: Brooks,Bill [mailto:[log in to unmask]] Sent: Tuesday, May 18, 2004 3:50 PM To: [log in to unmask] Subject: [TN] FW: [DC] Core Constructions Is there a materials expert out there that can answer Mike's question below? B-stage epoxy resin is somewhat of a mystery to many designers. Perhaps someone can clarify the reference to "High Resin Content" as apposed to ? what other options are available and how they affect the construction of the FR4 board. Please copy to the group too so we can all learn from this. Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 http://pcbwizards.com -----Original Message----- From: Mike Valle [mailto:[log in to unmask]] Sent: Tuesday, May 18, 2004 12:24 PM To: [log in to unmask] Subject: [DC] Core Constructions Hi, I need some help trying to find some information on FR-4 construction and thickness. I've come across a 4-layer stackup on a cross-section detail on one of our drawings and I can't seem to find it in IPC-4121. Our b-stage construction calls out for 1 ply of b-stage HRC (high resin content) 7628 .0068. Another detail on another drawing calls out for 1 ply of b-stage HRC (high resin content) 7628 .008. What I've been finding in IPC-4121 is that there is a FR-4 11 (7.087) 7628 40% RC and a HFR-4 11 (7.087) 40% RC, which is a high tg. So, my question is - is there such a thing as HRC - high resin content with varying thicknesses? Thanks, Mike Valle Project Engineer, PCB Design Shure Inc. 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