Hi Alex -
     
MELFs: fact or fiction? Well, that's the way many people look at them. We use 
MELFs in many of our designs with good success - now with that said, I don't 
like them. My major beef with them is that we are putting a round object on a 
flat surface - Mother Nature has rules that tell round things on flat surfaces 
to roll! Yes, the solder paste keeps the MELFs in place but the basic physics of
things rolling can still take place (kind of like putting a square peg in a 
round hole, a.k.a.. square pins in thru holes). As for the notched versus 
unnotched pad configuration - they both work and one isn't any better or worst 
for assembly purposes but the board designers don't like them. One other problem
has been solder fillet volumes. Your stencil thickness that optimizes for 0603 
chips, etc. will leave your MELF solder fillets somewhat starved which depending
on your use environment can be a problem. Assemble equipment can handle the 
MELFs but you do have to optimize your vision system, placement head speeds, 
etc. so you don't throw the parts on the manufacturing floor. MELFs are useable 
but I recommend you explore other options first. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]


______________________________ Reply Separator _________________________________
Subject: ASSY: MELF's
Author:  [log in to unmask] at ccmgw1
Date:    12/5/96 4:01 PM


     Techies:
     
     Our engineering department wishes to use a MELF package (National 
     Semiconductor LL-34) for a diode on a new design. They intend to mount 
     this part on the bottom side of the PCB. Last I heard, this type of 
     package caused major headaches and extra cost during assembly. Has 
     anyone out there used this package in high-volume production? What are 
     the known pitfalls today? What percentage increase in assembly cost can 
     we expect (if any)? What footprint works the best (SM-782 has 2 
     recommendations, one has notched pads to help keep the part from 
     rolling)? Any other gotchas we should be aware of? 
     
     Thank you in advance for your help - Alexis Meehan - ATI
     
*************************************************************************** 
* 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]      * 
***************************************************************************
     

***************************************************************************
* 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]      *
***************************************************************************