Electronics solder defects

It is beyond the scope of this chapter to provide a detailed explanation of SPC. Rather, there will be a qualitative discussion of process control that addresses those factors affecting circuit board assembly, beginning with defect types in electronic solder joints. Then the discussion will turn to process control as it pertains to the basic assembly steps (e.g., dispensing, pick-and-place, etc.). The various material sets (e.g., circuit board, solder paste, flux, etc.) will be incorporated in the discussion. Also, the use of Pb-free soldering technology will be addressed where applicable. 

Component Placement. The purpose of the component placement machine—also called the pick-and-place machine—is to select the proper component, orient it correctly, and then place it on the circuit board, all with degrees of accuracy and precision that minimize defects on the finished product. In addition, the component must be placed on the printed solder paste, the dispensed adhesive, or a combination of the two deposits with a controlled pressure or release distance that does not excessively spread out either material or damages the component package. Moreover, the placement machine must execute these tasks as quickly as possible in order to maximize the production volume. Lastly, the equipment must be sufficiently versatile to address continually changing electronic packages, specifically dimensions and I/O configurations. 

J-STD-002, Solderability Tests for Component Leads, Terminations, Lugs, Terminals, and Wires. This standard prescribes the recommended test methods, defect definitions, acceptance criteria, and illustrations for assessing the solderabihty of electronic component leads, terminations, solid wire, stranded wire, lugs, and tabs. 

Electroless nickel coatings can be easily soldered and are used in electronic applications to facilitate soldering of light metals such as aluminum. Electroless nickel is often used as a barrier coating to be effective, the deposit must be free of pores and defects. In the as-deposited amorphous state, the coating corrosion resistance is excellent (Table 12), and in many environments is superior to that of pure nickel or chromium alloys. However, after heat treatment the corrosion resistance can deteriorate. 

Visual inspection, refined over the years to identify defects and faults that have been correlated to mechanical property behavior and reliability in the field, is a very important aspect of the electronic assembly process. Accordingly, a set of visual inspection criteria has been identified and generally practiced across the industry for eutectic Sn-Pb solder joints. However, the mechanical properties, visual appearance, and solder joint geometry of lead-free solders, in combination with lead-free and lead-containing terminations, are markedly different from those of PbASn, as listed in Table 28. Therefore, new visual inspection guidelines must be developed [19]. 

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