When things go wrong on a zinc electroplating line, quick solutions can save thousands of dollars. If the answer is not pre- or post-treatment, the laboratory is the place to troubleshoot the plating bath. A quick analysis and a few hull cells may be all it takes to put the operation back on its feet. This paper deals with the investigative process in the laboratory.
First things First
Quick solutions to problems on an electroplating line can save thousands of dollars. Experience is by far the most valuable tool a troubleshooter can possess. So successful troubleshooting begins when the line is at its best! Build your experience by walking the line when everything is running smoothly. Take note of solution color, smells, gage settings, etc. Intimate knowledge of your plating line and its idiosyncrasies will expedite the solution to future problems.
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If you’ve ever purchased inexpensive jewelry with a fine coating of precious metal, then you’ve witnessed the end result of electroplating. It’s an electrochemical reaction used to put a fine metallic coating on an object. Aside from making cheap jewelry, electroplating has important uses in the automotive industry for chrome plating, and in the electronics industry for optics and sensors.
The process of electroplating (also referred to as electrodeposition) is fairly simple. To start, a negative charge is placed on the object that will be coated. The object is then immersed in a salt solution of the metal that will be used to plate the object. From there, it’s simply a matter of attraction; the metallic ions of the salt are positively charged and are thus attracted to the negatively charged object. Once they connect, the positively charged ions revert back to their metallic form again and you have a newly electroplated object.
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In another form of barrel plating operation, the parts lie at the bottom of an open cup-shaped tub rotatable about an axis at about 45o to the horizontal. There is a negative contact sited centrally in the base, and an anode is hung above the parts. The tub is filled with plating solution and rotated. For removal, the contents are dumped out through a sieve. Barrel plating does not produce such satisfactory deposits as tank plating, for the action on any one parts is at best intermittent and some parts may receive an inordinately thin deposit.
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Driven by the need for increased speed, portability and wiring density, the interconnect pitch on semiconductor packages, and the corresponding high density interconnect (HDI) substrates, continue to shrink. The combination of filled blind microvias and build-up technology provides a means to achieve the required wiring densities. With the rapid growth of this technology, the use of electrodeposited copper for filling blind microvias has become a widely adopted process for manufacture of both HDI printed circuit boards (PCBs) and also semiconductor package substrates.
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The development of modern continuous sheet galvanizing lines has led to the disappearance of most of the old manual mills for galvanizing cut sheets. There are however still some machines that galvanize cut-to-length sheets; they use chemical pretreatment sequence similar to those for wire or tube galvanizing.
At the beginning of the line, the end of one coil is welded to the start of the next coil. Then there are two basic methods for continuously galvanizing sheet which differ in the way that the strip is cleaned before galvanizing-chemically or by thermal treatments. Coils of annealed cold reduced sheet may be fed directly to the galvanizing line, or alternatively, coiled sheet is continuously heat treated in the pretreatment line. After leaving the galvanizing bath, in which strip only stays for a few seconds, the surface is wiped to remove excess zinc and may be further treated to after the surface appearance, composition, smoothness or mechanical properties.
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