Phil
Welcome to Board Talk. This is Jim Hall and Phil Zarrow, the Assembly Brothers, also known as consultants for ITM Consulting.
We have a question today from a AS who asks, "Dear Jim and Phil. Can you mix a leaded component and a lead-free component in the same circuit board and still say the product is lead-free even when you are using lead-free?"
Jim
If we're talking about the legal definitions defined by RoHS, the question is maybe. That is, what kind of lead are we talking about. There are some kinds of lead that are exempted under the RoHS law. For instance, if you have a fine pitch component like a QFP or a SOIC with a lead pitch of less than .65 millimeters then surface finish on those leads is exempt.
However, for most parts, chip capacitors, BGA's, and so forth, if you have any lead on one part on an assembly, that whole assembly violates lead-free as defined by RoHS.
So if we're talking about a chip capacitor that has a lead finish instead of a lead-free finish, and you put that on a board, that violates the lead-free legal status of that entire assembly.
There are also a number of sources of lead internal to the component, such as in the ceramics of capacitors and some of the internal solder joints in IC components that are exempted from RoHS. But if we're talking about surface finishes, I think with the exception of the fine-pitched parts, any surface finish on any individual component will put you in violation of the RoHS definition of a lead-free product.
So I hope that answers your question. The bottom line is don't mix your parts. If you want to be lead-free, get all the tin lead parts away from that area and maintain your inventories carefully. Once you get a tin lead part mixed in to your assembly anywhere, it's going to be hard to find and very expensive to correct if you need true lead-free status for RoHS or any of the other international legal requirements.
Phil
So beware of the caveats and know the rules and regulations. That should be it for Board Talk today and whatever you do and wherever you're doing it, whatever you do don't solder like my brother.
Jim
And don't want to solder like my brother and keep the lead out of those assemblies.
Use the form below to submit a comment.
Ashwin Kasi, Tellumat, South Africa
Here is the exemption in RoHS.
*23. Lead in **finishes of fine pitch components other than connectors with **a pitch of 0.65 mm or less** with NiFe lead frames and lead in finishes of **fine pitch components other than connectors with a pitch of 0.65 mm or **less with copper lead frames.[2010] *
There is no need for component manufacturers to follow this
exemption. It is my observation that most suppliers plate all their leads with Matte Tin regardless of the pitch.
You should read the RoHS document, it isn't that long.
Jim Hall, ITM Consulting
Ralph Longton, LoJack Corp
Asalene Coffey