Will A Few Failed Solder Joints Make Me RoHS Non Compliant?

[dad23honu]

Can a few failed solder joints cause my entire assembly to fail RoHS compliance? Let's say I have 400 lead-free components on a board. All were processed with lead-free paste, but some of the joints were cross-contaminated with leaded solder during touch-up. All of the components(and their accompanying solder joints) were shot with an XRF gun. Five locations failed with lead readings of 1300ppm, 2400ppm, 13,000ppm, 30,000ppm, and 153,000ppm. A few were in the yellow zone (around 950ppm), but the rest were in the None Detected through low hundreds ppm range. If I could calculate that the combined solder weight that I added to this assembly was below 1000ppm of lead, would I pass?

As I understand the RoHS directive, there must be no more than 0.1% (<1000ppm) of lead, when calculated by weight of raw homogeneous materials. Does my question make sense? If I can make the case that the combined mass of all of my solder joints (a single homogeneous material) is under 1000ppm of lead, should my assembly be considered RoHS compliant?

Or, does the failing of the "solder joints" on 5 locations make me out of compliance, when the solder joints on 395 locations are all within (or way below) spec?

 

[normzone]

Wow, [dad], I don't know the answer but I appreciate the opportunity to be educated at your expense, and I'll be following this thread with interest.

 

[dad23honu]

I had someone in another forum tell me that my described assembly would fail, so I posed the question in another way. I'll pose it here, too. It's long, but please bear with me.

I am assuming my PCB and my parts are all compliant, so let's take those out of the equation. I am adding lead-free solder paste to 5,000 terminations to make 5000 solder joints. Let’s assume that all 5000 solder joints are of the same size and require the same mass of solder. The solder that I'm adding is considered a homogeneous material, right? A single homogeneous material?

Now, let's say that during touch-up, a technician finds insufficient solder on a single chip resistor, and inadvertently adds leaded solder to both terminations of that resistor, and doesn't touch the rest of the board. I have 4998 solder joints that are all well below spec, and two solder joints on the aforementioned resistor that has leaded solder. If I shoot all 5000 joints with an XRF gun and 4998 joints all read "None Detected," and the other two joints read 2,000ppm (or 2X over spec, per joint), I think my assembly should still pass. The single homogeneous material that I added was solder. The overwhelming majority of it was lead free. Are you saying that my assembly would fail because two solder joints out of 5000 failed?

If so, this makes no sense to me. Let’s call the board I just described Board 1. And let’s say I have another board that we’ll call Board 2. Same board but processed differently. Let’s say the XRF gun detects 990ppm of lead in each of the 5000 solder joints. 990ppm of lead per solder joint is within spec, so the board is within spec, right?

You would have to agree with me that Board 2 (990ppm of lead per joint) has substantially more lead than Board 1 (0ppm of lead in 4998 joints, and 2000ppm of lead in each of 2 joints).

For the sake of argument, let’s say that each solder joint has a mass of 1,000,000 units of solder. Then 5000 solder joints would equal 5,000,000,000 units of solder, by weight. Board 2 has 990 units of lead per joint. Multiply that by 5000 joints and I have a grand total of 4,950,000 units of lead on my assembly. But, because I’m under 1000ppm per joint, this assembly is within spec, right?

Now, let’s look at my Board 1. The 4998 joints on this board are all reading zero for lead. But, two joints are reading 2000 units of lead, per joint (two times over spec). Add this up and I have a grand total of 4000 units of lead on my assembly. But this board fails?

By my calcuations, Board 2 has over 1200 times more lead, by mass, than Board 1. How would Board 1 fail and Board 2 pass?

As I understand the RoHS directive, there must be no more than 0.1% (<1000ppm) of lead, when calculated by weight of raw homogeneous materials. I believe that I make a good case that the combined mass of all of my solder joints (a single homogeneous material) is under 1000ppm of lead. Shouldn’t my assembly be considered RoHS compliant?

 

[normzone]

You've convinced me, and I thank you for the methodology of your argument.

Unfortunately, I'm a tyro at best at this matter. Somebody will be along shortly who either supports your argument or knows more than both of us, or just likes to argue

 

[Jaydub]

I am not a RoHS expert either. You appear to be trying to apply logic to the RoHS requirements and I don't think that is possible. My take is that each solder joint is a separate homogeneous material. So board #1 fails. Otherwise you could pick several connections, just use lead solder on them and claim that all solder joints are one. I don't think the bureaucracy would be happy with that, but I could be wrong.

 

[Big Jim]

What I do know is that I would never want to be in that position. That's just a sloppy manufacturing practice to not control leaded and unleaded solder better than that.

 

[pkost]

[caveat] I'm not a RoHS expert [/caveat] but I think you will struggle with this, taking a look at UK guidance (https://www.gov.uk/government/uploa...ohs-regulations-government-guidance-notes.pdf)

“Homogeneous material” means a material that cannot be mechanically
disjointed into different material.
27. The term “homogeneous” is understood as "of uniform composition throughout",
so examples of "homogeneous materials" would be individual types of plastics,
ceramics, glass, metals, alloys, paper, board, resins and coatings.
28. The term “mechanically disjointed” means that the materials can, in principle,
be separated by mechanical actions such as unscrewing, cutting, crushing,
grinding and abrasive processes.

You therefore can't consider all the solder on the unit to be one and calculate the average.

You probably can't even consider each joint to be homogenous as it may not be uniform throughout

 

[1010011010]

We produce electronics as well and sometimes have the same question. As long as your customer doesn't order lead free but RoHS compliant you are safe.

"For the purpose of this Directive ?homogeneous material? means one material of uniform composition throughout or a material, consisting of a combination of materials, that cannot be disjointed or separated into different materials by mechanical actions such as unscrewing, cutting, crushing, grinding and abrasive processes."

Therefore your whole PCBA is to be considered as a homogenous material and in that case you have to take the weight of the lead and compare it to the weight of the assembly. In this case even a PCBA soldered with leaded solder can be RoHS compliant.

In the automotive industry a big topic is IMDS (International Material Data System). There you have to break down your whole PCBA into all its substances and their weight percentage. One of the reasons is compliance with RoHS and REACH for the OEM at the end.

From my point of view you are safe, as long as your customer doesn't want lead free.

 

[pkost]

We produce electronics as well and sometimes have the same question. As long as your customer doesn't order lead free but RoHS compliant you are safe.

"For the purpose of this Directive ‚homogeneous material’ means one material of uniform composition throughout or a material, consisting of a combination of materials, that cannot be disjointed or separated into different materials by mechanical actions such as unscrewing, cutting, crushing, grinding and abrasive processes."

Therefore your whole PCBA is to be considered as a homogenous material and in that case you have to take the weight of the lead and compare it to the weight of the assembly. In this case even a PCBA soldered with leaded solder can be RoHS compliant.

In the automotive industry a big topic is IMDS (International Material Data System). There you have to break down your whole PCBA into all its substances and their weight percentage. One of the reasons is compliance with RoHS and REACH for the OEM at the end.

From my point of view you are safe, as long as your customer doesn't want lead free.

This is an interesting perspective on "homogenous". An entire PCBA is certainly not of uniform composition - how can it therefore be homogenous

 

[MIREGMGR]

I too am not a RoHS expert, but certainly with cutting and abrasive tools of appropriate scale for the tasks, I could separate a circuit board into epoxy from IC encasements, epoxy or other resin from the circuit board itself, glass or other reinforcement from the circuit board itself, parylene or other coating from the circuit board, copper from the circuit board, mixed metal from ICs, and so forth.

It's not appropriate, when considering a definition such as the one that PKost quotes above, to construct a biased case in which the hypothetical test is determined to fail because the hypothetical means of performing the test-task is deliberately non-optimal. Of course if one were to run a circuit board through a large shredder such as might be used for whole automobiles and the like, the result would seem to point to the circuit board having been a homogeneous material. That however is not the optimal approach for such a mechanical separation process. Clearly if the optimal mechanical approach is used, any circuit board is non-homogeneous.