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Issues in the SMT Process
The SMT industry’s one constant is change. Standards are continually updated and components are miniaturized for space savings. In addition to the changes that come, the industry is also faced with continuing to deal with areas that fail to change and update. A typical PCB manufacturer lays out a line based on the need to put solder paste on a PCB, place parts in the paste, and then reflow the product (Figure 1). The board size, typical components placed, and the required speed for the line are then considered.
Eventually, a SMT manufacturing line is purchased that can handle a large majority of the process needs. In almost all cases, there will be a component that cannot be handled by the automated process currently in use on the factory floor. This problem is not caused by the engineer who specified the line, nor is it the chosen vendor’s false advertising. This problem plagues virtually all PCB manufacturers because it is not cost-effective to purchase a specialty machine to handle a component that is expected to go away and not be used any more, or the component that is through-hole and was expected to be replaced by a SMT component soon.
Manufacturers are expected to build as demanded and very often that demand is outside of the specifications which they thought were adequate, but the quantity does not justify new special equipment. PCB manufacturers, for example, face the challenge of placing very large connectors, whose size is outside the specifications of SMT machines (Figure 2). Some manufacturers use through-hole components in products (Figure 3), though not enough need exists to justify purchasing a through-hole machine.
Infrequently used components may fail to justify standard packaging for use, and oddly shaped parts may simply be beyond the scope of what a standard SMT machine can handle. In addition to the difficulty in managing the changes in size and type of component for placement, manufacturers must also consider the cost-effectiveness of any solution they devise for managing these “out-of-spec” placement issues. Rarely do these issues justify the expense of purchasing a specialty machine. Rather, the manufacturer finds it more cost effective and more realistic to manage these processes with human resources.
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Editor's Note: This article originally appeared in the September 2014 issue of SMT Magazine.