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70 PCB007 MAGAZINE I SEPTEMBER 2021 A Few Caveats Debris issues aside, blistering or flaking of the electroless copper from the surface or in the holes can be attributed to the following: • Electroless copper process chemistry is out of balance. Adjust the components into the proper operating ranges and ensure that the con- trollers are maintain- ing the solution components at the proper feed rate. • Depending on solu- tion loading (square feet of board per gallon of electroless copper solution), the reducing agent level (formaldehyde) may increase in concentration. is can cause the solution to become overactive and result in the flaking or blistering problem. • Primary stabilizer in the electroless copper solution is low, leading to an overactive solution; deposition rate is higher than normal leading to blisters or flaking. • Plating racks with loosely adherent copper deposits can cause these defects. Regularly strip the plating rack to remove these deposits; the rack should be clean of copper before each plating cycle (Figure 5). Copper flaking from racks can destabilize the solution, causing rapid plate-out and rough copper deposits. • Monitor the specific gravity of the operat- ing electroless copper process. Maintain the specific gravity at or below the suppli- er's stated recommendation; high specif- ic gravity is an indication that the process may be overactive. • Process control: Regular replenishment additions based on square footage processes is ideal. A simple single- channel controller to monitor the copper content of the solution works efficiently. Other components are metered in accord- ing to pre-set pump settings. Do not wait to make large manual additions on an irregular basis. Remember that the genesis of a defect or anomaly is not readily evident within a partic- ular process or operation. e root cause may have multiple contributors. Be sure to look closely at the processes that may contribute to the defect. PCB007 Michael Carano is VP of technology and business development for RBP Chemical Technology. To read past columns or contact Carano, click here. Figure 5: Panels ready for processing. Note the stainless-steel racks are clean and devoid of copper deposits.