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Trouble in Your Tank: The Role of Organic Solderability Preservatives in Advanced Packaging
It’s Only Common Sense: Lighten Up!
Standing Room Only at ICT's Winsford, UK Seminar
In cooperation with Merlin Circuit Technology, deep eutectic solvent formulations had been evaluated as hot-air solder levelling fluxes with remarkable success. Copper was wetted more rapidly than with proprietary HASL fluxes and complete coverage was achieved in a single dip. One very interesting outcome was the ability to solder-level with lead-free solder on PCBs with electroless nickel finish, not previously achievable with conventional fluxes, and this opened up the prospect of a novel solderable finish dubbed Hot Air Solder Levelling on Electroless Nickel (HASLEN).
ICT Chairman Professor Martin Goosey gave the third presentation, entitled Recovery of Copper from PCB Manufacturing Processes using Crab Shells, describing the TSB-funded STOWURC project whose objective was to develop sustainable materials and processes using waste products from the seafood industry to treat effluent and recover metals from PCB manufacture.
The whole supply chain, from raw material to dissemination of information, was represented in the project consortium. It had been observed that a natural component of the shells of crustaceans, chitin, was able to adsorb heavy metals from dilute solution, and that a simple chemical modification of chitin, by alkaline deacetylation to form chitosan, significantly improved the efficiency of adsorption. For example, one gram of chitosan was capable of adsorbing 250 milligrams of copper.
Professor Goosey summarised the results of initial experiments. The effects on adsorption rates of parameters such as temperature, pH, initial concentration, rate of mixing, specific metal ions had been studied, over a range of chitosan parameters including the amount of adsorbant, the degree of deacetylation and the particle size. It was possible to reduce copper concentration in effluent to the 0.1 ppm level.
Having captured the metal, it was possible to desorb it with sulphuric acid and recover it by straightforward electroplating. A key issue was the residual adsorption efficiency of the chitosan after stripping of copper; there was a tendency for absorption ability to decrease with each cycle, and conditions were being optimised to minimise the effect.
Chitosan had the ability to adsorb a wide range of metals found in PCB effluent, nickel for example, and there were many applications in the general metal finishing industry. It also provided the opportunity to recover endangered or rare metals from low concentration solutions. Professor Goosey mentioned platinum, palladium, rhodium, osmium, iridium, mercury, and gold as examples, but made it clear that each metal would need an optimised combination of process parameters and conditions.
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