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Banned substance - Thiourea

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Joseph Khiew


Banned substance - Thiourea | 21 December, 2005

Dear all,

If anyone familiar with the banned substance, Thiourea which is used during chemical solution of pcb with immersion tin. We have check with some of the labs but they are unable to provide such test report for the thiourea content on bare pcb. Our customer insist us to give them the test report, and comment that it is the requirement as per US legislation. Would appreciate if anyone can help.

Best regards,


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Banned substance - Thiourea | 22 December, 2005

Immersion metal baths also rely on alchemy-like magic. If you take a piece of copper and dip it into an aqueous solution of silver ions: Presto Chango! Within seconds the copper will be coated with silver. Of course, there is some additional magic required to provide bath stability and consistency; this is the realm of the patent office. The tin bath is a bit more complicated due to the electromotive series. Tin is less noble than copper, so the chemists use thiourea compounds to rearrange this troublesome roadblock. Significant amounts of thiourea are needed. Besides other malodorous properties, thiourea is accused of some deleterious health affects. On top of all this, it can attack soldermask and poses a waste treatment concern. The chemical supply industry works night and day to come up with a usable alternative for thiourea compounds. [Going Beneath the Surface of Surface Finishes; Cullen, D; Circuitree 11/02]

While thiourea [CH4N2S] can be detected with liquid chromatography [HPLC] methods by many laboratories, consider contacting the licensor of the process that your board fabricator licenses. They should be able to give you abvice on testing and control methods and save you some effort since undoubtly they've paved this ground already.

Here's the MSDS for thiourea

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