The components do not suit the production technology - KingSheng PCBA

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Component selection is an important stage in the PCB design process. Within the selection process, characteristics examined are component functionality and suitability to design requirements, cost and availability. Yet another characteristic worth examining is the component’s suitability to the production technology. Selecting a component that’s a poor match forces use of other, nonstandard means of component soldering. This degrades the component’s soldering quality, increases work cost and prolongs production time.

Following are several examples depicting this issue:

A component that does not withstand the soldering temperature. When using the component to be soldered on a surface mount technology production line, verify the part withstands the typical soldering temperature. In SMT production, heat within the reflow oven can reach temperatures in excess of 230°C on average. Some components are defined as SMT, but their maximal soldering temperature, as stated in manufacturer’s data sheets, is 100°C, meaning that type of component must be assembled manually. In cases where large volumes are expected, this may significantly increase the assembly cost because, instead of automated component assembly on the regular production line, parts must be assembled by hand.

A component not designated for SMT soldering. Several components are defined as SMT components, but in practice are connected by copper wire using specialized machines called wire bonders. These components cannot be assembled on the conventional SMT production line. By the way, the cost of assembly is considerably higher for this type of component than that of a typical SMT part.

Unnecessarily selecting cutting-edge components. Components can usually be ordered in several package sizes. The smaller the package, the more complex the soldering in production, which may lead to non-optimal soldering quality. Sometimes engineers select the smaller option from among several alternatives of package sizes offered by the manufacturer: for example, a QFN with a package pitch of 0.35mm (the distance between the component’s leads), instead of a larger package with a pitch of 0.55mm or even 0.65mm. From an assembly perspective, the larger package is preferable and will lead to better soldering results in production. (The exception is if component density on the PCB is high and, as a result, utilization of smaller packages is unavoidable.)

Selecting a component that requires special assembly and installation equipment. There are components whose installation on the PCB requires custom equipment. This increases the PCB assembly cost and can also cause sub-optimal soldering results. Consider, for instance, an SMT connector that protrudes significantly from the edge of the PCB (FIGURE 1). Since the component’s tail is relatively long, its center of gravity is located outside the PCB; therefore, it tends to bend downward after machine placement. This bending on one side of the component, triggers a certain rising on the other side of the component thereby causing insufficient soldering between the lands and the component body. The addition of rims on the edge of the PCB will not help in this case, since the component body is higher than the PCB’s vertical zero axis. To perform optimal soldering of this component, custom equipment is necessary that will support the component body and prevent its downward bending. Use of such equipment adds expense and slows production.