PCB007 Magazine

PCB-Oct2016

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70 The PCB Magazine • October 2016 in the line. Check the quality of the plating solution. And walk the line! This last step provided some additional in- formation that must not be discounted. Upon first inspection of the plating cell, one noted that the plating rack on this particular cell did not seat properly in the contact saddle. One could see the space in the contact area. That is certainly not optimal with respect to achiev- ing electrical conductivity through the plat- ing cell, plating racks and to the circuit board. The greater the resistance in the plating cell, the less current flows to the circuit board. And from there one can surmise that the plating thickness and distribution will not be ideal. Poor electrical contact within the plating cell leads to high resistance which in turn affects plating quality. One of these symptoms mani- fests itself as "burned" or rough plating as shown in Figure 2. It is also prudent to inspect the electrical cables and their respective connections lead- ing from the rectifier to the plating cell. Are the cables of sufficient size to carry the current necessary to effect optimum plating distribu- tion? Or are the cables in such poor condition that some current is lost before the current can reach the circuit board? Inspect for the not so obvious! You will save yourself headaches and heartaches later. Secondly, analysis of the plating solutions told another story that needed to be addressed. This part of the story relates to the control of the plating additives in the acid copper plat- ing cell. In the plating cell showing the copper with the enlarged grain (Figure 2), the trouble- shooter found that two key additives required for the proper functioning of the acid copper process (organic addition agents and the chlo- ride ion) were extremely low. Indeed, analysis showed both to be well below the minimum required for optimum plating quality. There are myriad of addition agents com- mercially available. The function of these ad- ditives is to provide a mechanism whereby the copper deposit is plated in a level and ductile condition. Typically, the addition agent pack- age consists of grain refiners, leveling agents and suppressors. For purposes of this discus- sion, the grain refiner is used interchangeably with the term "brightener." The chloride ion plays a synergistic role with organic additives in the brightening and leveling mechanism, and also promotes even anode corrosion. (In a future column the author will present more details on plating additives.) For now, one needs to focus on the problem at hand. The plating cell in question was set up to have the additives added manually after analy- sis. However, it was discovered that a timely analysis of the plating additives was not com- pleted for over 36 hours because the opera- tor thought the panels looked good! Organic addition agents and other chemical additives such as the chloride ion have a major effect on plating quality. Upon analysis using CVS (cy- clic voltammetric stripping analysis) and the traditional Hull cell, it was clearly determined that the plating solution was severely low in the additive. When the low organic agent con- centration and low chloride ion situation was corrected, the plating condition shown in Fig- ure 2 was eliminated. For good measure, the plating saddles were adjusted to improve the contact between the plating rack and the plat- ing cell. Now, while the defective condition seen on boards plated in cell #2 was related to the plating additives, cell #1 (Figure 1) displayed a defect of a different origin. Clearly the de- fect in Figure 1 can be traced to particulate or insoluble material in the plating solution or on the surface of the printed circuit board. Again inspection of the plating cell showed that there was indeed particulate matter that was not being properly filtered from the plat- ing solution. While that was understood, the CASE STUDY: PLATING NODULES—WHERE DID THESE COME FROM? " Inspect for the not so obvious! You will save yourself headaches and heartaches later. "

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