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Automating Odd-form Component Assembly
December 31, 1969 |Estimated reading time: 7 minutes
With continued use of thru-hole components in mixed-technology assemblies, the challenge remains how to automate the assembly of odd-form components effectively.
By Wolfgang Jeutter
Despite advancements in surface mount technology, the majority of circuit boards still contain a variety of thru-hole components. Use of these devices likely will not disappear in the future due to electrical performance or mechanical requirements. Many of the remaining thru-hole components such as connectors, electrolytic capacitors, power diodes, relays and transformers are odd-form in nature.
The term odd-form refers to either thru-hole or surface mount components whose height, weight or shape cannot be placed automatically with standard pick-and-place machines. Odd-form components traditionally have been placed on circuit boards using discrete insertion machines, dedicated hard-tooled automation or manual assembly. Discrete insertion machines are best suited for applications with several odd-form components. They tend to become less effective for applications requiring a small number of odd-form components of different form factors. Dedicated hard-tooled automation has been used to meet the needs of high-volume, low-mix manufacturing. Production changeovers can be time consuming and inefficient with dedicated systems. They also require a dedicated and skilled technical support staff.
Manual assembly of odd-form components is suitable for either low part-count applications, low production-throughput requirements or a highly flexible high-mix, low-volume manufacturing requirement. Because manual assembly is labor intensive, it tends to be expensive and leads to offshore manufacturing gaining the immediate benefit of low-cost labor. While relocating production facilities offshore makes sense for companies whose products are distributed in global markets, it is not a realistic or economic option for every company.
Some industries can be affected adversely by offshore manufacturing due to supply chain logistics. North American automotive assembly plants, assembling both domestic brands and foreign nameplates, cannot afford potential production stoppages. For this reason, the majority of automotive electronics are sourced from supply chain partners located within close proximity to the auto assembly plant and linked by a responsive transportation infrastructure.
Challenges
In the past, odd-form insertion cells have had a limited range of flexibility, representing a high capital investment in relation to the limited number of components they could process. Previous automated odd-form equipment generally used specialized SCARA robots. While these stand-alone machines were an improvement compared to manual assembly, re-tooling was expensive. Until recently, justification of automated odd-form equipment was tied directly to insertion volume. The lack of equipment flexibility to handle a high mix of odd-form components also hindered previous automation attempts. With the domestic electronics industry shifting to a high-mix, low-volume manufacturing environment, the goal of enhancing flexibility and maintaining cost-effectiveness in odd-form assembly has taken center stage.
More flexible odd-form placement cells that can quickly reconfigure to meet a range of odd-form assembly applications are available. These automation cells accommodate an assortment of odd-form components and packaging formats, and are capable of rapid line changeover.
For intrusive paste-in-hole reflow applications, odd-form components are inserted into the board without clinching the leads. With the growing implementation of lead-free soldering, however, an increasing number of odd-form components no longer can be assembled using this technique. Some odd-form components, such as connectors manufactured from non-engineered polymers, cannot tolerate exposure to the higher peak reflow temperatures required for lead-free alloys. This is true for telecommunications and industrial boards, where approximately 70 to 80% of odd-form components are connectors of various forms.
Odd-form Assembly
The need to accommodate a variety of components and component packaging methods has lead to the advent of odd-form automation modules offering greater flexibility. A major consideration in automated odd-form assembly is the variety of parts that require board placement. This affects not only the number of component grippers that will be required, but also the number of feeders.
Wherever possible, the gripper fingers should grasp the component leads instead of the component body. Floating gripper heads can handle a variety of odd-form components but are susceptible to body-to-lead tolerance variation between different component manufacturers. Vision systems can be used to align component leads, but this lengthens cycle time and decreases output.
Equipping an odd-form automation module with gripper fingers adjusted to the form factor of each unique component improves lead-to-hole placement accuracy and overall system reliability. By using a multiple turret-head system, specific grippers can accommodate a wide range of odd-form components (Figure 1). The benefit of a multiple turret-head is that it allows the automation module to pick-and-place a variety of odd-form components sequentially.
Figure 1. Turret-head with multiple component-specific grippers.
Up to six odd-form components can be collected from respective feeders and placed in succession at corresponding locations on the board. Using this collect-and-place method, the movement of the turret-head is minimized. This method also is useful in reducing board transfer time.
Once feeding and insertion is accomplished, the next step is to ensure that the odd-form components are retained in the board. With the exception of paste-in-hole intrusive reflow, odd-form components generally are clincheded underneath the board to hold them in place before and during wave soldering. Passive and active lead clinching mechanisms are available for this task. Passive systems are suitable for a limited range of components and do not verify that the component leads have been inserted through the board. Assembly quality is improved with active lead clinching because this method uses a sensing system that verifies that leads are inserted through the board and components are inserted in the proper orientation.
An automotive electronics manufacturer recently launched three circuit board designs that required a total of five million odd-form placements per year. Previously, this manufacturer had been placing many of these odd-form components manually, but encountered challenges with increasing product quality and reducing labor-intensive costs. They decided to eliminate manual assembly completely to boost production levels and minimize assembly errors. They chose an assembly module* that feeds and places a range of odd-form components regardless of their size, shape or packaging format to accomplish this.
Five different odd-form components had to be placed on three different boards, requiring four unique grippers for the component form factors. The odd-form components were supplied in different packaging formats, requiring several feeder types (Table 1). Radial capacitors were supplied in a tape-and-reel format, tube feeders were used for transistors, diodes and a vibratory bowl feeder was required for a power connector that was supplied in bulk.
The company decided to process boards as single units because specialized test fixtures were equipped to handle single boards. After odd-form assembly, the boards are placed in wave solder fixtures to position the semiconductors at a right angle to the board and hold them against a heatsink during wavesoldering. Holes for the odd-form components are 0.016" larger than the lead diameter to aid assembly and provide adequate lead-to-hole fill during soldering.
Flexibility
Quantities of all board types had to be produced interchangeably within any given production shift, therefore a flexible, odd-form automation cell was needed. To facilitate rapid changeover, the range of odd-form components, packaging formats, feeder types and component-specific grippers had to be housed within a common assembly cell. The assembly module met this requirement, producing all board assemblies with a common setup without exchanging feeders or grippers (Figure 2). Only a different placement program needs to be activated, resulting in virtually zero changeover time between board types.
Figure 2. Interchangeable feeders in a common odd-form assembly cell.
A high degree of accuracy and repeatability was needed to ensure precise insertion of odd-form components and to reduce placement defects. The assembly module was designed to meet this type of requirement with its linear drive motors and a placement accuracy of ± 25 microns at 5 Σ.
The component leads of odd-form parts requiring trimming or forming can be cut automatically to length and formed inside the feeders. Leads that are not tapered can also be cut at an angle to provide a lead-in, making the insertion process more reliable. The assembly module also is equipped with automatic tube exchangers to replenish the supply of odd-form components and increase system productivity.
Placement program changes are carried out on the fly from a centrally located touch-screen, where the Windows 2000-based software can be accessed in multiple languages. The assembly cell is SMEMA compatible and can communicate with other assembly line equipment both upstream and downstream. With a 66" footprint, the assembly module can fit into a customer’s existing production line.
The assembly module used has a placement rate of 1,800 cph with a cycle time of 2.0 sec per odd-form component. Placement performance can be increased for certain applications by using a multiple gripper head to pick-and-place up to five odd-form components simultaneously.
Conclusion
Mixed-technology circuit boards continue to challenge the odd-form assembly process. Given the recent focus on enhanced flexibility, innovative solutions such as automated assembly modules should be considered for the assembly of odd-form components.
* inLine.speed assembly module, Manz Automation, Inc.
Wolfgang Jeutter, vice president, Manz Automation, Inc., may be contacted at (401) 295-2150; e-mail: wjeutter@manz-automation.com.