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!:read: :(

Thanks -Steve

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.

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.

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

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

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:agree1: 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.

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

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...:frust:

The JEDEC SOLID STATE TECHNOLOGY ASSOCIATION (JEDEC) may have some info for you. We use JEDEC standard JESD 97 for RoHS labeling requirements.

Attn: Publications Department
2500 Wilson Blvd. Suite 220
Arlington, VA 22201-3834
Fax: 703.907.7583

Regards,

Dirk

The persistance of trace elements like mercury can be amazing - at one time I worked for the only US company producing high purity vacuum grade chromium. To get chrome content we analyzed for a slew of elements (a hihly technical term :D ) and then subtracted from 100%. Mercury was one of the elements we analyzed for, and if memory serves was present at the ppb level. The material in question had gone though a high temperature (> 2800 F) at low vacuum levels (equivalent to outer space levels) for an extended cycle - total cycle including heat up and cool down was 10 days. We still found traces at the ppb level.

In general, my opinion is that if you keep analyzing to finer and finer levels, eventually you can find almost any element in most materials. Of course, you've need acess to some expensive equipment to do the analyses.

BTW: If I understand your original question, it appears that you are attempting to justify the amount of Pb by expressing its weight as a fraction of the overall weight of the flex. If this is the case, I believe that your premise is incorrect in that the RoHS requirement is for less than 1% by weight of the "homogeneous" materials. The European Commission’s own documented guidelines defines homogeneous as the individual components that make up a product, where if they were to be separated they would no longer exhibit their individual characteristics (i.e. solder, copper wire, enamel, etc.).

With this in mind the fact that 60/40 solder/tinning is being used already tells you that it is non-compliant in that the solder (a homogeneous material) contains greater than 1% Pb.

BTW: If I understand your original question, it appears that you are attempting to justify the amount of Pb by expressing its weight as a fraction of the overall weight of the flex. If this is the case, I believe that your premise is incorrect in that the RoHS requirement is for less than 1% by weight of the "homogeneous" materials. The European Commission’s own documented guidelines defines homogeneous as the individual components that make up a product, where if they were to be separated they would no longer exhibit their individual characteristics (i.e. solder, copper wire, enamel, etc.).

With this in mind the fact that 60/40 solder/tinning is being used already tells you that it is non-compliant in that the solder (a homogeneous material) contains greater than 1% Pb.

Thanks David. This has been a "point of confusion" for us here since we've been trying to understand the RoHS requirements - i.e. "What is a homogeneous material?"... If the Sn/Pb is electrodeposited on a flex, is it still a "seperate" material? If our flex weighs 1 gram, the transducer weighs 100 grams, then you're saying (or the EU is saying...) it doesn't matter that this is a coating or how it's applied? In the extreme, this would imply that any single solder joint in any size device, it it's 60/40 Sn/Pb, would disqualify the entire device! THAT'S INSANE!!:bonk:

We haven't done any calculations yet on mere Sn/Pb weight, but if what you're saying is correct, then it doesn't matter what calculations we do - we're non-compliant right out of the gate.:confused: I guess I now know why there are so many exemptions and why the electronics industry was so "up in arms" when this was first proposed!

If the Sn/Pb is electrodeposited on a flex, is it still a "seperate" material? If our flex weighs 1 gram, the transducer weighs 100 grams, then you're saying (or the EU is saying...) it doesn't matter that this is a coating or how it's applied? In the extreme, this would imply that any single solder joint in any size device, it it's 60/40 Sn/Pb, would disqualify the entire device! THAT'S INSANE!!:bonk:

We haven't done any calculations yet on mere Sn/Pb weight, but if what you're saying is correct, then it doesn't matter what calculations we do - we're non-compliant right out of the gate.:confused: I guess I now know why there are so many exemptions and why the electronics industry was so "up in arms" when this was first proposed!

This is exactly the reason that the electronics industry has been striving to move towards an acceptable replacement for Pb/Sn solder (of which there are many variaties today).

Let's look at the calculations in the other extreme (BTW: the is an actual scenario that played out with one of our suppliers). If as a supplier, I provide you with a choke that in total weighs 4 lbs. (most of which is the copper wire wrapped around a small ferrite core) and I tin approximately 1/4 of an inch of each of the resulting 6 leads of this wire - the percentage of Pb in this tinning compared to the overall weight of the wire is miniscule. With this understanding in order to be compliant I really don't have to reduce the amount of Pb I'm putting into our environment, all I have to do is increase the amount of wire/weight that I'm using.

If the purpose of the EC Directive is to eliminate/reduce hazardous materials from our environment, which of these practices makes the most sense?

OK - Let's bag the whole association w/ RoHS and all it's political and business implications...

Just a basic chemistry question - If I know the composition of a flex circuit trace of given size, can I use that information to calculate the amount of lead by weight? I know;

Length and Width of trace.
The fact that it's 1-oz. copper (35.4 um thick)
Tin/Lead plating thickness (in this case 200u-in)
Tin/Lead percentage

Is there a formula into which I can plug in this known info and calculate the amount of lead by weight (or tin or copper for that matter)? I'll worry about the regulations later - I'm just looking for a method, formula, etc.

OK - Let's bag the whole association w/ RoHS and all it's political and business implications...

Just a basic chemistry question - If I know the composition of a flex circuit trace of given size, can I use that information to calculate the amount of lead by weight? I know;
Length and Width of trace.
The fact that it's 1-oz. copper (35.4 um thick)
Tin/Lead plating thickness (in this case 200u-in)
Tin/Lead percentageIs there a formula into which I can plug in this known info and calculate the amount of lead by weight (or tin or copper for that matter)? I'll worry about the regulations later - I'm just looking for a method, formula, etc.Steve, since you know the length, width, thickness of the plating and the % of lead. (l)(w)(t)(.4)=the volume of lead Now you can go here to calculate the mass or weight (http://www.allmeasures.com/Formulae/static/formulae/density/20.htm). Then convert it to % weight of the total assembly.

Thanks Al!!! I should have guessed there was a web site somewhere that would help me out without having to resort to digging back into my old Chemistry books! This is great.

Of course, now I have the dilema presented by David...:(

I would hope that the EC on RoHS would come up with a reasonable ruling when considering the solder connections to PZT... but time will tell.

Thanks again Al.

-Steve

Steve, since you know the length, width, thickness of the plating and the % of lead. (l)(w)(t)(.4)=the volume of lead Now you can go here to calculate the mass or weight (http://www.allmeasures.com/Formulae/static/formulae/density/20.htm). Then convert it to % weight of the total assembly.

You'll probably be close enough with this formula, but keep in mind that solder tinning is NOT "plating". Applying solder is a chemical reaction that takes place at a molecular level, it is not the simple bonding of a solder to the copper, but is the creation of several layers of intermetallic bonds that are comprised of various percentages of copper, tin, lead, and their various compounds.

My point is that the "pure" copper lead diameter is actually reduced, while the "tinning" changes the structure of the outer layers - so the "thickness" of the Pb (lead) content may actually be a fraction greater than specified.

All of which will more than likely be immeasurable as a percentage of the overall weight.

You'll probably be close enough with this formula, but keep in mind that solder tinning is NOT "plating"...

But our flex circuits ARE plated - I believe I'm using the correct terminology. The sheets of etched copper are placed in a bath, electrically charged and are wet plated to a given thickness on both sides of the trace (for the purposes of discussion, 200 micro-inches on each side). We verify this thickness using XRF when the flexes arrive and, within reason, the plating thickness is fairly close to nominal. We then reflow this solder onto our PZT ceramic elements.

There are other places within the transducer where we do "tin" using standard 60/40 solder - but in the case I was asking about, it is a plated flex. Am I missing something, or was this just a misunderstanding early on? I know there are different way of plating (sputtering, wet plating, etc.) and these flexes are wet plated.

-Steve

But our flex circuits ARE plated - I believe I'm using the correct terminology. The sheets of etched copper are placed in a bath, electrically charged and are wet plated to a given thickness on both sides of the trace (for the purposes of discussion, 200 micro-inches on each side). We verify this thickness using XRF when the flexes arrive and, within reason, the plating thickness is fairly close to nominal. We then reflow this solder onto our PZT ceramic elements.

There are other places within the transducer where we do "tin" using standard 60/40 solder - but in the case I was asking about, it is a plated flex. Am I missing something, or was this just a misunderstanding early on? I know there are different way of plating (sputtering, wet plating, etc.) and these flexes are wet plated.

-Steve

You are correct--the circuits are being electroplated (http://www.ppc1904.com/products.html) with Sn/Pb. It's a common practice in PCB and connector manufacturing, and different from (for example) wave soldering.