Chemical tin immersion plating solution used for suppressing tin whisker growth of printed circuit board and plating method

Abstract

The invention belongs to the field of printed circuit board preparation, and provides a chemical tin immersion plating solution used for suppressing tin whisker growth of a printed circuit board and aplating method. Through metal achieving the function of blocking through deposition in the chemical tin immersion process, generation of a copper-tine alloy is suppressed, and the aim of eliminatingtin whiskers is achieved. The chemical tin immersion plating solution comprises at least one kind in tin salt with the concentration ranging from 20 g/L to 30 g/L, nickel salt with the concentration ranging from 10 g/L to 40 g/L and cobalt salt, a reducing agent with the concentration ranging from 20 g/L to 50 g/L, a complexing agent with the concentration ranging from 0.1 g/L to 50 g/L, a stabilizer with the concentration ranging from 1 g/L to 10 g/L and a pH adjusting agent. Compared with a traditional printed circuit board surface finishing technology, by means of the chemical tin immersionplating solution, the growth rate of the tin whiskers can be greatly reduced, the aim of suppressing tin whisker growth is achieved, growth of tin whiskers on the surfaces of devices is greatly reduced, and good application prospects are achieved.

Description

technical field [0001] The invention belongs to the field of printed circuit board preparation, and relates to a plating solution and a plating method for chemically immersing tin on the surface of the outermost copper circuit of a printed circuit board (PCB), in particular to a PCB outermost coating capable of inhibiting the growth of tin whiskers. A plating solution for chemical immersion tin on the surface of a layered copper circuit and a plating method. Background technique [0002] In the process of preparing printed circuit boards, in order to ensure the performance of the printed circuit boards such as solderability during subsequent assembly and use, it is necessary to perform a final surface finishing treatment on the surface of the circuit. Common surface finishing methods include hot air leveling, chemical nickel-gold plating, organic solder protection film, chemical immersion tin, chemical immersion silver and other methods; among them, chemical immersion tin ha...

AI Technical Summary

Problems solved by technology

Aiming at the causes of tin whiskers, people have invented some methods to inhibit the growth of tin whiskers. Michael Hundt of STMicroelectronics in "Controlling Tin Whiskers in Lead-Free Assembly" releases the stress by annealing the tin plate to reduce the stress. To achieve the purpose of inhibiting the growth of tin whiskers, the study found that the coating after high temperature treatment for a certain period of time will not appear tin whiskers when stored at room temperature for 400 days, but after high temperature treatment, the thickness of the solderable layer will be reduced, and the printed circuit board will be reduced. Solderability; He Yanfeng, Sun Jiangyan and other researchers proposed to add specific fine additives in "Research on Additives for Lead-Free Pure Tin Electroplating" to prevent tin atoms from diffusing along the crystal by changing the structure of the tin layer, thereby inhibiting the generation of tin whiskers , this method can also effectively inhibit the growth of tin whiskers, but after using additives, the surface of the coating will be darker and affect the performance of the coating such as solderability; mechanical pressure will cause compressive stress inside the coating, so it is necessary to protect the device from External forces such as mechanical pressure or scraping can also inhibit the growth of tin whiskers to a certain extent; Lee B and other researchers have shown in the literature "Spontaneous growth mechanism of tin whiskers" that the stress in the coating comes from the copper-tin interface. Copper-tin co-compounds formed between them, so some researchers disclosed a plating solution with organic metal additives in US Patent No. 5,858,074, by dipping a layer of colorless benzene complex film on the bare copper surface to be welded. A protective layer is formed between copper and tin to avoid the formation of alloy compounds between copper and tin and effectively suppress the generation of tin whiskers. This method does prevent the formation of alloy compounds between copper and tin, but after the film is stripped, a film may remain on the copper surface Residue, after several thermal cycles, it is difficult for the solder to effectively immerse the via hole, and the OSP active ingredient imidazole will degrade and decompose after several thermal cycles, which will affect its ability to protect the copper surface and solderability

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