Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Chris Grendler

#13217

Pad Sizes | 24 December, 1998

I need advice on a pad design which several other engineers whom I work with would like to try. I think it is an utterly crazy but I can't seem to convince them differently.

My current 0402 chip pad sizes on alumina and FR4 substrates are .022"X.015" and the pads are spaced .030" center to center. In other words the complete footprint is .045"x.022". I believe this pad layout is very small when compared to IPC land guidelines. The product my company produces is very miniature so PCB real-estate is very important. I can live with the .045"X.022" footprint. However, in order to put more circuitry on the PCB, the design group wants to go to pad sizes that are 60% of .022"X.015". They then believe I can over print the 60% reduced pad with solder using a stencil appeture of .022"X.015". I am up against about 10 coworkers who range from design engineers, process engineers, and production managers who all believe this is a great idea. I believe I know the problems which will occur if this idea is persued.

Solder balls due to solder paste printed off the metal conductor pads, I can't believe I will get much of a solder fillet since the component will be bigger than the pads, maybe tombstoning will occur, I would also think the component will float on the solder and will end up tipped after the solder cools, I hate to think what will happen if the component is placed 50% off the pads by the pick and place machine

The production manager says he used undersized pads for 0402 components where he worked before and it really helped to keep components aligned to the pads.

Please give me a sanity check. Maybe I am too closed minded.

reply »

former co-worker of yours

#13218

Re: Pad Sizes | 30 December, 1998

| I need advice on a pad design which several other engineers whom I work with would like to try. I think it is an utterly crazy but I can't seem to convince them differently. | | My current 0402 chip pad sizes on alumina and FR4 substrates are .022"X.015" and the pads are spaced .030" center to center. In other words the complete footprint is .045"x.022". I believe this pad layout is very small when compared to IPC land guidelines. The product my company produces is very miniature so PCB real-estate is very important. I can live with the .045"X.022" footprint. However, in order to put more circuitry on the PCB, the design group wants to go to pad sizes that are 60% of .022"X.015". They then believe I can over print the 60% reduced pad with solder using a stencil appeture of .022"X.015". I am up against about 10 coworkers who range from design engineers, process engineers, and production managers who all believe this is a great idea. I believe I know the problems which will occur if this idea is persued. | | Solder balls due to solder paste printed off the metal conductor pads, I can't believe I will get much of a solder fillet since the component will be bigger than the pads, maybe tombstoning will occur, I would also think the component will float on the solder and will end up tipped after the solder cools, I hate to think what will happen if the component is placed 50% off the pads by the pick and place machine | | The production manager says he used undersized pads for 0402 components where he worked before and it really helped to keep components aligned to the pads. | | Please give me a sanity check. Maybe I am too closed minded. |

I would agree with most of your comments, Chris. Since you did not give the exact sizes being proposed, I can only make a few comments:

-Solder balls are certainly to be expected -Solder fillets may not meet IPC Class X requirements (maybe this is not a concern)

Your other comments would need further testing to prove/disprove. I certainly would be on your side.

S

reply »

ii-feed SMT Intelligent Feeder

Reflow Oven