Standard pad sizes for reflow and wave

We've noticed that there are many different recommendations for pad sizes for various SMT parts. This seems to vary wildly from manufacturer to manufacturer for the same case sizes. Is there any standards that can used used to specify these sizes? Also, how does this vary based on reflow soldering versus wave soldering.

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| We've noticed that there are many different recommendations for pad sizes for various SMT parts. This seems to vary wildly from manufacturer to manufacturer for the same case sizes. Is there any standards that can used used to specify these sizes? Also, how does this vary based on reflow soldering versus wave soldering. | Hi Paul, have you tried the online calculator on the IPC page. After years of trial and error I have the CAD-people in my present company now focused on that very useful page. Every new entry in their database is now checked with that tool and, who would have thought, the first shot hits ( presuming you have a reliable datasheet for that component ). Unluckily the improvements do not effect the old jobs and we still have to build enough of them but as they die the padmismatch is gonna die. There are also some books available but I wouldn�t suggest taking anything without checking with the datasheets.

Let�s hope for a better future

Wolfgang

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| | We've noticed that there are many different recommendations for pad sizes for various SMT parts. This seems to vary wildly from manufacturer to manufacturer for the same case sizes. Is there any standards that can used used to specify these sizes? Also, how does this vary based on reflow soldering versus wave soldering. | | | Hi Paul, | have you tried the online calculator on the IPC page. After years of trial and error I have the CAD-people in my present company now focused on that very useful page. Every new entry in their database is now checked with that tool and, who would have thought, the first shot hits ( presuming you have a reliable datasheet for that component ). Unluckily the improvements do not effect the old jobs and we still have to build enough of them but as they die the padmismatch is gonna die. | There are also some books available but I wouldn�t suggest taking anything without checking with the datasheets. | | Let�s hope for a better future | | Wolfgang | I agree with wolfgang, the IPC page is a good place to start, for wave however the sizes are a little on the conservative side so I would normally hedge on the Max condition as the start point and add a littledepending on the complexity / orientation / closeness of components.

JohnW

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| We've noticed that there are many different recommendations for pad sizes for various SMT parts. This seems to vary wildly from manufacturer to manufacturer for the same case sizes. Is there any standards that can used used to specify these sizes? Also, how does this vary based on reflow soldering versus wave soldering. | Paul,

The IPC recommendations are probably a good place to start BUT they do not cover all cases. E.g. for wave soldering, QFPs are often put at 45�, requiring different sizes for optimum and "robber" or "thief" pads can be very useful, where space permits, to reduce bridging. If you post-solder clean, then a new can of worms is opened, because you have to ensure there is enough space for solvents/water to get in under them damn components.

The best document I know of to answer your question is Chapter 5 (Guidelines for Design of Footprints) of "Manufacturing Techniques for Surface Mount Assemblies" by R.J. Klein Wassink and M.M.F. Verguld (Electrochemical Publications Limited): this chapter is 50 pp long (see http://www.elchempub.com )

Hope this helps

Brian

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| | | We've noticed that there are many different recommendations for pad sizes for various SMT parts. This seems to vary wildly from manufacturer to manufacturer for the same case sizes. Is there any standards that can used used to specify these sizes? Also, how does this vary based on reflow soldering versus wave soldering. | | | | | Hi Paul, | | have you tried the online calculator on the IPC page. After years of trial and error I have the CAD-people in my present company now focused on that very useful page. Every new entry in their database is now checked with that tool and, who would have thought, the first shot hits ( presuming you have a reliable datasheet for that component ). Unluckily the improvements do not effect the old jobs and we still have to build enough of them but as they die the padmismatch is gonna die. | | There are also some books available but I wouldn�t suggest taking anything without checking with the datasheets. | | | | Let�s hope for a better future | | | | Wolfgang | | | I agree with wolfgang, the IPC page is a good place to start, for wave however the sizes are a little on the conservative side so I would normally hedge on the Max condition as the start point and add a littledepending on the complexity / orientation / closeness of components. | | JohnW |

You can try IPC SM 782 and 782A for surface mount device.....

hope that helps...

dreamsniper

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| We've noticed that there are many different recommendations for pad sizes for various SMT parts. This seems to vary wildly from manufacturer to manufacturer for the same case sizes. Is there any standards that can used used to specify these sizes? Also, how does this vary based on reflow soldering versus wave soldering. | Paul: Let's get basic.

1 When you print paste to be reflow soldered, you contol the amount of paste available to make a solder connection by selecting the size of the aperture and thickness of stencil or screen and by printer process control. 2 When you solder SMT components with a wave, you have no control the volume of solder available to make a solder connection. It's virtually unlimited. You can control the volume applied to a connection by pad design and wave solder process conrol.

Why do you care about the volume of solder in a connection? Too solder reduces the reliability of solder connections. You know, that's why all the standards try to get you to produce concave fillets and limit the amount of flow up the sides of vertical faces of chip terminations, etc ... There has been studies to support this contention that you can obtain.

Should you care about the volume of solder in a connection? Dunno ...

1 A medical device firm I know allows no wave soldering of SMT devices. 2 A DEC (Compaq) employee presented on DFM to our SMTA meeting said they used the same pads on both sides.

Go get 'em.

Dave F

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