Technical Library | 2020-07-29 20:12:52.0
Aluminum is a metal that it is hard to solder due to the high surface tension difference between it and molten solder alloy. This occurs because aluminum rapidly forms a tenacious oxide layer whenever it is exposed to oxygen in the air. The oxide layer is responsible for the high surface tension difference between the aluminum and the solder and impedes the solder from spreading evenly on an aluminum surface. There are hundreds of aluminum alloys available in the marketplace; it is important to identify the form of aluminum that is being soldered. Once this is done, an appropriate soldering technique can be chosen for soldering the specific aluminum alloy under consideration. Direct aluminum soldering eliminates using expensive plating techniques to prepare the aluminum surface for soldering.
Technical Library | 2022-10-11 17:27:08.0
Lead-free flux technology for electronic industry is mainly driven by high soldering temperature, high alloy surface tension, miniaturization, air soldering due to low cost consideration, and environmental concern. Accordingly, the flux features desired included high thermal stability, high resistance against burn-off, high oxidation resistance, high oxygen barrier capability, low surface tension, high fluxing capacity, slow wetting, low moisture pickup, high hot viscosity, and halogen-free. For each of the features listed above, corresponding desired chemical structures can be deduced, and the impact of those structures on flux residue cleanability can be speculated. Overall, lead-free flux technology results in a greater difficulty in cleaning. Cleaner with a better matching solvency for the residue as well as a higher cleaning temperature or agitation are needed. Alkaline and polar cleaner are often needed to deal with the larger quantity of fluxing products. Reactive cleaner is also desired to address the side reaction products such as crosslinked residue.
Technical Library | 2014-06-23 14:50:52.0
It was unusual to see chip terminations change colors when tin lead solders were used but with the introduction of lead free reflow soldering and the corresponding increases in reflow temperatures terminations are now changing colors. Two conditions are present when reflow temperatures are increased for lead free solder alloys that leads to discoloration. Reflow temperatures are above the melting point of tin (Sn MP is 232oC). Air temperatures commonly used in forced convection reflow systems are high enough to both melt the tin plating on the termination allowing it to be pulled into the solder joint due to solder joint liquid solder surface tension leaving behind the exposed nickel barrier. Now those metal oxide colors will be visible due to high air temperatures during reflow.
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