Introduction of lead-tin alloy electroplating in PCB industry printed circuit process!
Dec 15, 2021
In the process of printing circuit boards, the surface of the steel strip usually has a plating printing process for lubrication, bonding and soldering. This process is known in the industry as electroplating lead-tin alloys. This paper briefly introduces the function and mechanism of dielectric electroplating of lead-tin alloys.
The element symbol of tin is Sn, the atomic weight is 118.7, the density is 7.29g/cm3, and the electrochemical equivalent of Sn2 is 2.214g/Ah. The symbol of lead element is Pb, the atomic weight is 207, the density is 11.4g/cm3, and the electrochemical equivalent of Pb2 is 3.865g/Ah.
Tin-lead alloy plating is a protective layer for alkali etching in the production of printed circuit boards. In this case, the lead content in the coating is not critical. When hot melt is required after etching, a 60-63% tin-lead plating must be provided. The coating should be uniform, fine, semi-bright, 8 microns thick. The coating does not require full brightness, depending on the application of the coating. In an acidic solution, lead and tin electrodes have similar potentials and are easy to co-deposit. In order to obtain different ratios of lead-tin alloy coatings, lead and tin ion concentrations and cathode current density can be controlled. Fluoroborate baths are widely used in industry.
The tin-lead alloy plating solution should have good dispersibility and deep plating ability, stable process and easy maintenance. There are many kinds of electroplating solutions, but the main ones are fluoroborate type and non-fluoroalkyl sulfonate type. The fluoride bath is stable, easy to maintain and low cost, and has become the most widely used process in PCB production for many years. However, in recent years, more and more attention has been paid to the pollution of fluoride, and the amount of fluorine-free electroplating solution is also increasing rapidly. Alkyl sulfonic acid tin-lead alloy plating solution has become more and more mature in recent years, and the prices of materials and additives have also become reasonable, and the dosage has increased year by year. At the same time, additives are no longer a single imported product, and the quality and quantity of domestic additives have been significantly improved.
