Hi! Dave, you asked about the reasons for large conductive areas. >May I ask a dumb question ???? IMO very seldom is a question asked on the technet dumb, that's why technet's here and (collectively) we are here to communicate requirements, knowledge and experience. >If the 8 square inch area is unbroken, then what is it used for? It is >obvious from your statement that there are no isolation clearances, or >isotherms for holes, so this precludes the use of either leaded or SMD >components on the surface of the board. Could it be that your designers have designed a feature that may be very costly that serves >no obvious function?? >I'm curious... It's the "ultimate" SMT design and assembly, everything is located on one-side --- (;-) just think if we could eliminate the dielectric and only use "self-supporting" conductive patterns. Seriously though, some designs are such that all components and conductive patterns may form a single-sided board and assembly with all components and conductive patterns located on one-side. This is particularly desirable and achievable for some analog/RF designs. In particular, some very high frequency and microwave design can be implemented in "single-sided" designs. Sometimes this is very desirable for mixed designs, consisting of analog and digital, or analog and analog (where there are some very sensitive (low level) analog and "higher" power analog in the same design. The full ground/voltage planes (with no holes) are used as "signal conductor reference ground planes" to maximize electrical "E"-field isolation from one side of the assembly to the other. This is particulary true in the case of analog/digital, where analog is located on one-side and the digital is located on the other, with (ideally) only one through connection from one-side-to-the- other. Most printed board conductive patterns provide minimal (like no) "H"-field magnetic isolation, shielding or attenuation due to the characteristics of most printed board conductive pattern materials (like copper, tin, lead, etc.). In some cases, lands are attached to the low impedance "ground" plane using "blind" vias, and the supply voltages are very carefully routed on the conductive pattern layer. >Dave Rooke >Circo Craft - Pointe Claire >Date: Tue, 10 Sep 1996 20:33:26 -0400 (EDT) >From: [log in to unmask] (D. Rooke) Dave, hope this helps in understanding why some printed boards and their assemblies are designed as true "single-sided" designs or "doubled" single-sided assembly designs. Ralph Hersey Ralph Hersey & Associates [log in to unmask] *************************************************************************** * 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. * ***************************************************************************