Hello everyone, In response to the posts about the chip resistor networks, I'd like to share something I've learned. These are great little parts, they provide for very efficient use of PCB real estate, and for efficient machine utilization too. You're placing multiple resistors in one machine placement cycle instead of just one resistor per cycle. The ones I've been using recently are 4-resistor RPACKS that basically are four 0603 resisistors grouped together into one package...each resistor is on a .031" pitch from the other. We were putting 16-per of these on the backside of some Level-2 "Pipeline Burst" Cache' memory modules and double-side reflowing them. When we first started using them we were experiencing a lot of bridging and mis-alignment with these little puppies. I double-checked placement accuracy, tweeked the reflow profile, and also modified the stencil openings to cut down on some of the paste I was depositing to try and resolve this problem. All that helped somewhat, but didn't completely resolve the issues. Then I discovered that there are two different termination styles. They're called different things depending on who you talk to; Convex and Concave, Leaded and castellated, and one of my favorites; "Outie" and "innie". But basically, they're like this: _______________ | | _______________ | | |_ _| |__ __| _) (_ __|---------|__ |_______________| | | |_ _| |__ __| _) (_ __|---------|__ |_______________| | | |_ _| |__ __| _) (_ __|---------|__ |_______________| | | |_ _| | | _) (_ |_______________| |_______________| Convex, Leaded, or "outie" Concave, Castellated, or "innie" The above is a crude illustration of a 4-resistor RPACK and shows basically how the network is arranged, it also shows the two types of terminations. With the Convex RPACK's, the solder fillet is formed at the end of each resistor. On the Concave RPACK's the fillet is formed in the small indentation at the middle of each resistor...kinda' like how LCCC's are. The point of all this is that I met with some gentlemen from Phillips (who also make these things) and they shared with me a report from a study that their Product Application Group did to see if there were any valid reasons as far as performance, reliability, or manufacturability to make two different termination styles. What they discovered was that with RPACK's with Concave terminations had much, much better yeilds during assembly than did Convex styles. This was due to the Concave style's ability to "self-center" itself during reflow if placement was less than perfect...and from experience, they are "absotively" right! I've got a copy of the report and some beautiful color pictures of before and after reflow that shows the difference between each style RPACK. The report also has recommended footprints and pad geometry's for the components too. I know that the IPC-782 doesn't have a footprint out for this part yet, so if anyone would like it, jes' ask! Ya'll know how ta' get in touch wif' me... __\/__ . / ^ _ \ . |\| (o)(o) |/| #------.OOOo----oo----oOOO.-----# # Steve Gregory # # [log in to unmask] # # # #________________Oooo.__________# .oooO ( ) ( ) ) / \ ( (_/ \_) *************************************************************************** * 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] * ***************************************************************************