We have analysed the oxide development on and in the tin surface during ageing (155 °C). We tested a tin on copper surface after a tinning time of only 5 minutes after pretreatment with ORMECON compared to no pretreatment. The "lower oxides" mentioned are mainly (or are assumed to be) SnO, the "higher oxides" mainly SnO₂.

The results can be summarized as follows:

With ORMECON pretreatment: (oxide layer thickness / virgin 2 nm)

All samples except the 8 hrs (which is critical) are fully solderable.

The main change occurs during the first hour of ageing:
2 SnO ---> Sn + SnO₂,
parallel to
SnO + ½ O₂ ----> SnO₂
and Sn + ½ O₂ ----> SnO₂
accompanied with an increase in oxide layer thickness, but no decrease of solderability.

During the next hours of ageing, only the amount of SnO is being reduced, but the over-all oxide layer thickness does not change any more (no further increase). There is a gradual continuous change to be seen. Maximum oxide thickness 3 - 3.5 nm.

Without ORMECON pretreatment: (oxide layer thickness / virgin 3 nm)

This sample starts with a higher oxide layer thickness compared to the ORMECON one, and changes to the higher oxides much quicker (all SnO is being lost after 1 hour). In the first hour, there is only 2 SnO ---> Sn + SnO₂.

Parallel to that, a continuous increase of the oxide layer thickness can be observed up to 4 hours, then an interconversion to intermetallic oxides takes place (6 hours).

After 8 hours, a huge content of intermetallic oxides has built up, plus higher Sn oxides on top of it. Oxide layer thickness after 4 - 8 hrs: 6 nm and more.

Only the first 3 samples are fully solderable, with 4 hours and more, it gets critical to "not solderable".

In conclusion, these measurements show the second effect of why ORMECON prevents the loss of solderability: the oxide development is suppressed and chemically more defined, no intermetallic oxides are being formed (the first effect was, that the pure Sn layer does not decrease so quickly as in tin deposited without ORMECON).

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