RoHS Lead (Pb) Weight Calculation on paper before we begin costly testing

[Steve McQuality]

I searched the forums and didn't find an answer to this question. I'm looking for a way to do an initial calculation of the lead (Pb) content in our devices on paper before we go out and begin costly testing.

We manufacture Medical Devices. I know that these are currently exempt, but we have a customer who is asking for our current status. We have Pb in our PZT ceramic (specifically exempt) and Pb in our Sn/Pb solder joints. I'd like to try calculating the Pb weight in our solder connections. I'm thinking this might not be too difficult.

I know that we have 1-oz. copper (35.4 um thick) and I know width and length of the plated portion of our flex circuit. I know our desired nominal plating thickness of Sn/Pb in micro-inches. Can I use this data to calculate a theoretical nominal Pb weight using the volume (LxWxH) of the connection and molecular weights? My thought would be to figure how much Pb is in the flex circuit and then compare the calculation to the actual weight of the device to find the overall (calculated) Pb percentage by weight.

Can anyone direct me on how to perform this calculation? My college chemistry classes are merely a distant memory at this stage of the game!

Thanks -Steve

[Jim Wynne]

I'm sort of thinking out loud here, but it seems to me that if you know the Sn/Pb breakdown of your solder (say, 90-10, e.g., which is by weight) you could weigh soldered and unsoldered boards to get the weight of the solder, then calculate from there.

[Steve McQuality]

Originally Posted by Jim Wynne

I'm sort of thinking out loud here, but it seems to me that if you know the Sn/Pb breakdown of your solder (say, 90-10, e.g., which is by weight) you could weigh soldered and unsoldered boards to get the weight of the solder, then calculate from there.

These are electroplated flex circuits we receive from our flex vendor. They already have the Sn/Pb on them (60/40 Sn/Pb) so we are just reflowing them when they arrive to make the connection. For the solder joints we add, we've had just that thought - weigh before and after and figure it out from there. However, with these flexes, I'd need to get the weight before plating. Since they are "panelized", I'm not sure if our vendor could provide that info - that's why I'm looking to calculate it "afte the fact" so to speak.

[martin elliott]

Before doing this if this material is desined for the EU I suggest you take a look under the page within Wikipedia, the free encyclopedia (Redirected from RoHS). Search for Wikipedia RoHS as to some background and restrictions

[Al Rosen]

What about the other 5 elements? Have you looked into xrf equipment?

[Steve McQuality]

Originally Posted by Al Rosen

What about the other 5 elements? Have you looked into xrf equipment?

Actually, we're way ahead of the game on that one! Since we do a lot of plating in-house, we already have an XRF machine that we use for verifying plating thickness on ceramic we plate in-house (also use if for incoming plating thickness verification from our flex vendors). The XRF manufacturers rep was just here in Dec. and told me a lot of companies were using our model for verifying RoHS compliance. That's going to require some additional training to understand that aspect of our XRF - and when we get to the point of actual measurements, we're that much futher ahead. He showed me some of the elemental analysis capabilities of our machine - pretty cool The flex we were looking at showed the Tin, Copper, Lead spikes (Alpha, Gamma & ?? spikes on the spectrum) as well as some calcium - didn't know Ca was there - but it was!

I was looking for a method of "ballparking" our current status on paper before we began down that path. As for the other 5 - I'm pretty sure we're OK on those elements. ...of course, we may get surprised when we do actual analysis! As far as I know - Lead (Yep, it's there), Mercury (shouldn't be present at all), Cadmium (doubt it), Hexavalent Chromium (also doubt it), PBB & PBDE's (our platics division tells me "no"). Pb is our biggest "worry" at this point.

[Al Rosen]

Some of these elements are used in wire insulation, so you may be surprised there.

[Steve McQuality]

Originally Posted by Al Rosen

Some of these elements are used in wire insulation, so you may be surprised there.

We use one of the major medical cable suppliers (you can probably guess who if you're at all familiar with medical devices) and they have put "medical cables" on their back burner because of the reported exemptions. We're primarily concerned with the transducer that we're going to be attaching to the front end. We cannot control the cable composition at this point - not enough clout...