Fluxless Soldering of Copper Substrates Using Self-Assembled Monolayers for Preservation

Self-assembled monolayers (SAMs) of octadecanethiol have been used as a preservative to enable fluxless soldering of copper substrates. The SAMs were deposited onto copper surfaces that had previously been etched to remove any existing oxide layers and wetting balance testing under an inert atmosphere was used to measure their fluxless solderability as a function of storage time and environment. It was found that SAM coated samples could be stored in air at room temperature for a short period of time before they became unwettable as a result of oxidation, however this storage time could be greatly increased by keeping them at low temperature. X-ray photoelectron spectroscopy was used to monitor the level of oxidation within the materials, which was found to correlate with the fluxless solderability. The SAM is thought to present a barrier to the penetration of oxygen to the copper surface, but at the same time can be readily displaced by heat and molten solder