Bob and fellow Technetters, The situation you are describing usually refers to cross- graining the core material (usually short) vs the prepreg (usually long). You are only going to be compensating the core material (C-stage) Thus you will be maintaining the most stable configuration for the core in its' longest direction. At one time due to glass widths and laminator sizes there was an economic advantage to buying material this way for 18 X 24 panels, i.e. you got to use the edges of the glass for prepreg but not for core material because the laminators have to trim off the edges after lamination just like we do. I mention this only because it could have been the cross-plying got started. One of those good accidents. The last time I did an informal census of what people were running it went about 1/3 cross-plying, 1/3 straight-plying and about 1/3 who didn't know or didn't care. MY OPINION (did'nt used to be that of my employer but is now) At one time we were forced to run straight-ply on 20 x 24 panels due to availability. ln certain cases we would encounter, that most dreaded of process problems saddle warp, due to unbalanced board designs (usually odd shaped internal ground areas). After the laminators increased their press sizes we were able to convert everything to cross-ply and the problems with the larger panels went away. I also feel like the overall dimensional stability of the panels, as encountered when trying to register soldermask, improved. It also seems plausible that drill accuracy may improve slightly on smaller holes. Why, because most glass styles are not even, more threads/inch in one direction than the other. Given a balanced construction, cross-plying gives the entire package the same amount of glass going one way as the other. Of course there are a lot of other warpage issues (both process and material related) And no doubt other solutions. I can only say that there are certain part types we will not even consider running without cross-plying. Hope this makes sense and helps: Robert E. Welch Process Specialist Email: [log in to unmask] Modem: 804-239-9120 Fax: 804-237-3048 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************