land patterns for Pb-Free componet soldering

Hi All,
Is there any standard that we should follow for land patterns for Pb-Free componet soldering?

Thanks
Ricky

IPC-7351
**broken link removed**

the IPC7351-B is using rounded rectangle pad shape for many components, even the chip. Rounded pads are better for lead-free surface mount assembly using reflow, because lead-free solder doesn't flow as well as leaded solder and the aperture openings in the paste mask stencil are rounded corners. It may also benefit low profile components since it reduces the paste used.

Waste of time, increase size of gerber file ands generaly make life difficult, I'd stick with standard retangular pads, IPC-7351 spec and the various wizzards gives you the choice. would be hardpressed to recall a customer or company that actually uses rounded rectangles. There were problems with lead freein the early days and some AOI machines would fail assemblies because of the flow problems. but in the last few years I haven't seen the problem as much (lead free is now a mature process, having been around for 10+ years with some companies and at least 8 with others) and processe, fluxes, solder pastes have moved on.
The problem with Gerber (and ODB++) with rounded rectangles is these often have to be drawn instead of flahed (depending on CAD system used), greatly increasing the size of the files. For paste screens there are some advantages, but generally the process of creating the screen means that the corners are never super sharp, but tend to have a small radius on them.
Some bottom terminated components have bullet shaped pads to match the shape of the pad, but for others I dont bother,its extra work and hassle over a problemthat is not as big as it was origionaly thought to be.
Just my view, having tried both types in the past and workinng with numerous customers, I have found no real advantage.
Marc

So general stanadards for land pattern design can be implied for lead-free designs. I think only immprovement that can be made is using rounded rectangular pads, also this will reduce EMI problems that might occur due to sharp corners of rectnagular pads.

Wot, I dont thinks so. With EMC you have more things to worry about on the board, rectangular pad corners aint one of them, dipole and monopole structure created by the routing are gonna give you problems.
To be quite honest, around 2002-2007 did a lot of work with firms having babies over moving to lead free, didn't change any footprins or the way layouts were done, but did change surface finish to ENIG from HASL, and apart from production process changes and these being more closely monitered and controlled and implementing moisture control for boards and components that was it.
Still have millitary designs that are the same, that go through both processes without any problems.

Hi Marce,

Thanks for your thread on this issue but in my last thread t I did not meant to say that rectangular pads are the only source of EMI issue in a PCB and sorry if it sounded like that but I meant that rectangular pads are one of the issues of EMI.
I have a problem that my hardware designer is admant that I give him some document on land pattern design for lead-free soldering.

Can someone please help me on this.

T&R
Ricky

PM me with an e-mail address and I go through my docs etc and put somthing together for you. It will be IPC-7351 based cos thats the world standard for footprint design these days.
For now look up "The Cad library of the future" and have a look around here:
https://www.pcblibraries.com/

Sorry to go on about rectangular pad corners but like right angle tracks, they dont emit like some think, the RA track is a problem cos it adds an impedance missmatch.