Reposting to assist "repairing PCB" thread. On 31 August 2010 01:30, RussellMc wrote: >> "FR4 is essentially glass - epoxy resin laminate.with bromides >> >> incorporated to provide self extinguishing properties. >> Usually routed rather than punched. >> >> CEM3 (more Japan and some other Asia) is glass-epoxy but instead of a >> woven fabric as in FR4 uses random non woven glass fibres. Instantly >> distinguishable by its white colour. Equally as good as FR4." >> >> So under what conditions might a person choose CEM3 over FR4? Is it >> suitable for SMT? > > I can only tell you what I've read (but it sounds OK :-) ) > > The two sound largely interchangeable and it may be geographic ; and > availability factors may predominate. =A0CEM3 is said to be wholly > equivalent to FR4 for practical use. > It's widely used in Japan and much less so in US and Asia. I note that > a Hong Kong supplier offers both FR4 and CE3. I've not seen CEM3 > offered here but it may well be available. The key difference appears > to be that CEM3 uses random oriented fibres (probably equivalent to > saying CSM or chopped strand mat) whereas FR4 uses woven glass mat. > CEM3 is an opaqish white colour. The random orientation is said to > provide a material with isotropic mechanical properties. - suggesting > that FR4 may have somewhat different mechanical properties in various > axes - not something you'd expect to be =A0a major issue in PCB use > where glass PCB is usually substantially "stronger" than needed to > prevent mechanical failure. > > > Note that this is NOT true of phenolic paper PCB material and maybe > marginally true of epoxy-paper material. These material will happily > fracture and crack propagate under mechanical stress. Note the recent > vehicle recall mentioned =A0where a PCB fracture was causing problems in > some controllers made by only some sub contractors. No reasons were > given but one could guess that a change of PCB material may be the > cause. > > Relatively (even more) uninformed comment: I FR4 is not nice to punch. > Routing is usually used when slots etc are required. I'm not sure of > the limiting factors but the combination of glass mat and general > strength is probably hard on tools and the mat also tends to stop the > holes being clean. Some material I have read implies that CEM3 may be > better but that may be due to other factors - ie AFAIR CEM3 was being > used in very thin form and being punched for watch use. The thinness > may have been the main factor. > > This wide ranging PCB materials reference contradicts several things > that I have said above :-) - and looks extremely useful. > It notes: =A0 =A0 =A0 =A0 =A0 CEM-3 is similarly impregnated with epoxy r= esin > and has woven glass cloth surfaces, but its core of non-woven matte > fibreglass is more compatible than CEM-1 with through-hole plating. > CEM-3 is much more suitable than FR-4 for punching and scoring, and > its smoother surface gives better fine-line capability. > > =A0 =A0 =A0 =A0http://www.ami.ac.uk/courses/topics/0233_abm/index.html > > PCB maker - happened upon with above search - looks at least interesting > Claim a VERY wide range of capabilities and products. > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0http://bit= ..ly/PCB_Viafine > > They say here (DOC file) > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 http://bit.ly/zzzPCBViafi= neCapabilities > > 5. CEM-3 > =A0 =A0 =A0 =A0Very low Z-axis thermal expansion coefficient. > =A0 =A0 =A0 =A0Electrical, thermal & chemical characteristics similar to = FR-4. > =A0 =A0 =A0 =A0Like CEM-1, it punches cleaner than FR-4. > =A0 =A0 =A0 =A0CEM-3 is excellent for plated-thru-hole applications. > =A0 =A0 =A0 =A0CEM-3 as an alternative to FR-4 for both single & double-s= ided > product in the U.S. > =A0 =A0 =A0 =A0Very good flatness, thermal resistance and dimensional sta= bility. > =A0 =A0 =A0 =A0Outstanding thermal conductivity. > > 6. FR-4 > =A0 =A0 =A0 =A0Material has the best flexural strength and dimensional st= ability. > =A0 =A0 =A0 =A0FR-4 is very abrasive and greatly reduces die life as comp= ared to CEM-1. > =A0 =A0 =A0 =A0Punched-hole quality (excessive fibers) is not nearly as g= ood as > CEM-1and CEM-3. > =A0 =A0 =A0 =A0FR-4 has been the standard for plated-thru-hole applicatio= ns, > > > _________ > > And another > > =A0 =A0 =A0 =A0 =A0 =A0http://www.npc.com.tw/emd-new/di1/c/2009pdf/Data%2= 0Sheets/71~73-CEM-3-92%20_UV%20BLOCK%20CEM-3-92.pdf > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .