Oxidation of gold-plated circuit boards is a common issue in the printed circuit board industry. Through cross-departmental collaboration to analyze the problem and implement corrective measures, Jingpeng Circuits successfully resolved this quality issue. This article provides a detailed analysis of the causes, characteristics, and corrective measures for oxidation of gold-plated circuit boards.<\/p>\n
Oxidation of gold-plated boards is caused by impurities contaminating the gold surface; these impurities adhere to the gold surface and, upon oxidation, cause discoloration. In fact, gold is an inert metal that does not oxidize under normal conditions; however, impurities adhering to the gold surface\u2014such as copper ions, nickel ions, and microorganisms\u2014are prone to oxidation and degradation under normal environmental conditions, forming oxides on the gold surface.<\/p>\n
Contacting gold surfaces or gold plates with dirty gloves or finger cots, or coming into contact with dirty work surfaces or pads; this type of oxidation covers a large area and may appear simultaneously on multiple adjacent pads; it has a lighter color and is relatively easy to clean.<\/p>\n
During the water rinse following gold plating and the final board rinse, impurities in the rinse water adhere to the gold surface; this type of oxidation covers a small area and typically appears at the corners of individual pads, taking the form of distinct water stains; After the gold-plated board is rinsed, water droplets remain on the pads. If the water contains a high concentration of impurities and the board temperature is high, the droplets will evaporate rapidly and contract toward the corners. Once the water has completely evaporated, the impurities solidify at the corners of the pads.<\/p>\n
The primary contaminants in the water used for post-gold-plating rinsing and in the rinsing process of finished-product washing machines are microorganisms. Tanks that use deionized (DI) water are particularly conducive to microbial growth. The best way to check for contamination is to touch the hard-to-reach corners of the tank wall with your bare hands to see if the surface feels slippery; if it does, this indicates that the water has been contaminated.<\/p>\n
If the chemical solution in the through-holes or partially plugged holes is not thoroughly rinsed away, or if moisture remains inside the holes, the solution will slowly diffuse along the hole walls to the gold surface during the finished product\u2019s storage phase, forming a dark brown oxide layer.<\/p>\n
The gold layer exhibits poor density, while the nickel layer shows signs of slight corrosion; furthermore, the oxidized areas contain an abnormal amount of copper. This copper is most likely the result of copper ion migration caused by the poor density of the gold-nickel layer. Even after removing this oxidation, it will reoccur, posing a risk of re-oxidation.<\/p>\n
The walls of the on-site board-curing tanks at the Hualin plant and the washing tanks of the finished product washing machines are quite dirty. When touched by hand, the tank walls feel noticeably slippery, indicating the presence of mold. Remedial measures:<\/p>\n
Perform a minor maintenance and water change during each shift; conduct a major maintenance once a week. During major maintenance, soak the tank with hydrogen peroxide (2-5%) and sulfuric acid (3%); connect the water from the nickel-gold plating stripper to the inlet of the gold plating tank; The separate DI water line should be cleaned once a month, with the Environmental Protection Department establishing the cleaning schedule.<\/p>\n
The final rinse in the chemical gold plating line is a hot water rinse. Since the boards are still quite warm before being blown dry, this can easily cause water spots. Solution: Change the first rinse in the plating line to hot water and the final rinse to cold water.<\/p>\n
After gold plating, the gold-plated boards were not cleaned promptly and were left exposed to the air for an extended period. Remedial measures: Adopt the \u201cfirst-in, first-out\u201d principle to ensure that gold-plated boards are not left exposed to the air for more than ten minutes before cleaning, and that they do not remain in the curing tank for more than 30 minutes.<\/p>\n
Oxidation at partially plugged holes is caused by residual cleaning solution inside the holes. Remedial measures: During cleaning, position the board with the BGA-dense side facing down, reduce the board-cleaning speed, and appropriately increase the ultrasonic frequency. Additionally, clean the deionized water storage tank and supply lines with a hydrogen peroxide and sulfuric acid solution once every quarter.<\/p>\n
After a week of hard work, through cross-departmental collaboration to analyze and implement the aforementioned improvement measures, the issue of oxidation in the gold-plated boards has been completely resolved. Through measures such as strictly enforcing operating procedures, optimizing the rinsing process, and strengthening the management of tank cleaning, we have effectively reduced the occurrence of oxidation defects in the gold-plated boards, thereby improving product quality and customer satisfaction.<\/p>","protected":false},"excerpt":{"rendered":"
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