Leadfree dip soldering

Rob,

Are you hinting that the lead content of this component with dipped tin/lead solder would not be an issue with RoHS?

If so, our understanding is that the legislation requires that the 6 banned substances cannot exist at greater than X% in any one homogeneous material. Specifically in a transformer, some of the homogeneous materials would be: Lead frame material, lead plating, copper wire, wire coating, magnet, plastic housing. None of these materials, individually, can contain more than the X% specified in the legislation.

I bring this up because there seems to be a wide range of interpretation regarding what homogeneous means. Our company is proceeding down the path of most resistance as that is what our interpretation is. We are a CM and we have some customers that are hanging their hats on a component level measurement and were having to debate the issue.

Can I get a witness?

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Hi Hoss,

I was speculating - there are others out there with more experience in this field than me, who may know the definitive on this. I've heard rumours on transformers but nothing concrete.

But I was guessing that the transformer (as a whole) would be treated as a single component.

Cheers,

Rob.

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I do not mean big, heavy transformers but rather small ferrite core transformers, with ferrites in the range of EF16 .. EF40. The weight of the lead and its percentage of the total weight is not the issue here. We simply do not want lead-containing through-hole transformer pins coming in contact with leadfree alloy on our wave soldering machine and contaminating the solder pot.

The problem with soldering seems to do with temperature here. So far we have been using temperatures of up to 500�C and dip times of no more than 2-3 seconds (with Sn/Pb alloy). If we take the SN100C3 or SN100C4 leadfree alloys (copper contents 3% and 4%), we cannot go much higher than 400�C. This simply is not enough to burn off the PU and silk/nylon insulation of the leads - within reasonable time at least. If we increase the dip time, the plastic material of the bobbin core starts to melt, the pins start to come off the bobbin or get all twisted and you have a ruined transformer.

Another problem is the alarming rate at which copper from the leads starts dissolving into the Sn/Cu alloy as we increase temperature. Within not very many seconds you will have lost something like 20% of the wire thickness so the individual strands become very brittle and break easily. Not to mention the increase in the copper content of the alloy as a result of this dissolving taking place. A typical dip soldering machine only has something like 3-4 kg of alloy so the alloy gets off balance very quickly.

Soldering could be done by pre-tinning the wires prior to wrapping them on the pins but unfortunately this is not an option in automatic production.

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