Proper circuit handling is a big issue, both for the manufacturer during the build process and for the end user at assembly. Damage due to improper transport and assembly is an issue for the PCB “hardboard” industry, but is magnified when handling a “softer” flex-circuit. Polyimide and Mylar are easily damaged when they come in contact with a sharp connector pin or other metal component. Sometimes the best efforts to handle circuits in a “one up” configuration go awry during the many processing steps involved in final assembly.

It has been my experience that damage to the flex is most likely to occur during pre-heating and cleaning operations. Note the glass transition temperature of acrylic adhesive is 103°F (39.4°C). When pre-heating a flex for component assembly (typically around 225°F/107.2°C), the circuit softens making it extremely prone to surface damage from poor handling. Often, I see that the “common” practice during degreasing operations is to “dump” circuits en masse for ultrasonic cleaning, a clear foul leading to severe cover scratches and gouging.

The most common method of shipping a flex circuit to an end user is in a heat sealed bag. The bags are then grouped in larger numbers and placed into a secondary bag prior to boxing. For smaller robust circuits, this method provides adequate protection while keeping shipping and handling costs low. As circuit size and complexity rise, this method becomes less effective. Here is where the proverbial “ounce of protection” can indeed provide a “pound of cure.” Custom packaging is the answer.

When my own company experienced increasing returns for “damaged circuits,” we quickly realized most were due to follow-up processing at our customers facility. No one wants to point a finger at their customer, so we looked for an answer that would benefit both parties. By designing custom trays for handling raw flex circuits and follow-up assembly we can gain significant reductions in scrap. A custom tray not only protects better during transit but we also find our customers really like them on the production floor.

Figure 2

A properly designed tray should be able to support both shipping and assembly needs. Space considerations should not only be made for the flat circuit, but also allow for components that may be installed after arrival at the customer’s facility. Trays can be manufactured from a variety of plastics, each offering unique advantages. Figure 1 shows a “stackable” tray utilizing a static preventative coating, critical for circuits with active components. The clear tray allows for individual inspection without the need for circuit removal. This cuts down on inspection handling. Figure 2 shows a more typical “black plastic,” anti-static tray with an integral cover. This can be a good solution for larger, heavier parts.

In summary, while a custom shipping tray can add a significant layer of protection, proper handling during assembly cannot be understated. Protection from damage falls to both the flex manufacture and the end user. A careful review of incoming inspection and assembly procedures can significantly reduce scrap from poor handling. Packaging of raw PCBs is often over looked, but can be an important step in assuring a quality part reaches your end customer.