Through-hole automation challenges: new applications push the boundaries of mature technologies.

Problem

A new radio frequency (RF) application using mature through-hole technology requires several design changes, including insertion angles and clinching techniques, to optimize board functionality and reduce solder bridging.

The design standards and practices for high-volume radial component assembly were established several years ago to facilitate automation. Tooling and registration holes, edge clearances, component lead-hole sizes, physical component size and assembly angles were all standardized to optimize component packaging, board design and insertion throughputs. Typical machine speeds now exceed 20,000 components per hour.

One user had specific requirements outside the design standards. The product needed to integrate RF signals, control electromagnetic energy within the circuit and use radial components. Components were strategically placed on the printed circuit board (PCB) to minimize the effects of RF signals on the functional design. Several radial components were then arranged in an off-axis position, as shown in Figure 1. The radial component assembly design standards would only allow orientations in 90[degrees] increments. The layout also created many opportunities for defects such as solder bridging. The board design presented some distinctive challenges for the manufacturing assembly process that could not be accomplished with standard high-volume radial assembly equipment.

[FIGURE 1 OMITTED]

Problem Solved

Some possible alternatives were to place the delicate components manually or to convert the design to a surface-mount design; however, both alternatives were deemed inadequate. Beyond the obvious cost disadvantages of a manual assembly operation, operators often had to place their hands and wrists in awkward positions to insert certain components in the board, causing an unacceptable number of carpal tunnel injuries. Converting the design to eliminate radial components was expensive not only for the engineering effort, but also because the new materials would substantially increase the cost of the product.

The company worked with the automated equipment supplier to simplify the product design and modify the machine to accommodate 1[degrees] theta increments. The modifications were specifically developed to offer automation solutions for off-axis component insertion and were achieved by designing a number of complex software routines that command two interrelated servo-controlled axes.

The next challenge to overcome was the potential solder bridging of the components once the leads were cut and clinched in the boards. Components were so densely populated that using standard cut and clinch tooling created several solder bridges on certain areas of the board. The solution was to change the typical 45[degrees] outward angle clinch to an inward angle by redesigning the tooling to bend the leads in the opposite direction.

Today, new products can use mature technology, such as radial assembly, to satisfy several applications effectively. Although standards were designed to optimize high-volume automation, new challenges still require customized tooling and design changes. Users and equipment suppliers can work together to overcome the challenges they face.

John Giangrieco is a senior applications specialist in the Insertion Machine Division of Universal Instruments Corp., Binghamton, NY; e-mail: giangrie @uic.com.