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I've just received a batch of assembled PCBs where the manufacturer changed the previously used HAL-process to OSP.

Now there is a lot of open copper on the pcb, like on big inductors which "suck" a lot of the solder paste to their leads. There also is a blank surface now which was never meant to be covered with solder paste but only with the Tin from the HAL-process to keep the area leveled.

Does anybody have a clue how that "open" copper might change in the future? Is the protection of the OSP still their after soldering or will the copper start to oxide now?

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I guess your doubts arise from the look of the PCBs, where the copper may look like it hasn't been treated at all.

This document Precoplat refers to on its website says

The varnish forms an airtight cover to the copper surface and “allows” the processed boards a storage life of 6 months maximum. Increasingly, after this time, the encapsulated surface protection characteristic is gradually lost.

So your boards should be safe for half a year, which sounds reasonable. (If your PCBs remain in storage longer than that between production and assembly it looks like you're having a logistics problem.)

Areas which don't receive solder (paste) before soldering are no longer protected after the soldering, since the OSP layer breaks off at temperatures above 150°C (same document).

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Normally,OSP film can be kept effective within half year in the condition of room temperature without influence of acid or alcali.

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    \$\begingroup\$ Since you work in PCB manufacturing, consider to expand your answer to add useful content; by now what you say it's included in Steven's answer (a year ago). \$\endgroup\$ – clabacchio Mar 30 '12 at 7:53

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