Today, there are well over 3,000 companies that manufacturer printed circuit boards (PCB) in Asia (China, Taiwan, Japan, India, Korea, Thailand) with the supply capacity continuing to grow well ahead of the global demand.
This means that many of these manufacturing shops are looking for ways to do things that others can’t do in order to grow their business (As a side note, many of these shops are choosing just to lower prices in order to compete but as costs continue to rise in Asia this strategy has not been very successful). One of the things that some of these shops try to do is expand their services by providing flex and rigid-flex circuits to their customers.
This makes sense to them because “technically”, you use all of the same equipment to make a flex/rigid-flex board that you do to make a traditional rigid PCB. Most of these factories quickly find out that the manufacturing process, equipment, and expertise to be successful at manufacturing flex/rigid-flex parts are much different than they are used to.
The following is a list of technical challenges that every customer should ask their flex or rigid-flex pcb manufacturer.
1. Do they manufacturer their own flex circuits?
In my 15 years of experience in working with PCB manufacturers in Asia, a good 75% of companies that say that they make rigid flex PCBs outsource the flexible circuit board part of the process. While outsourcing as a concept is not a bad thing, when you outsource one of the most critical components of the end product, it always causes challenges.
Start with delivery; these manufactures are outsourcing this product to a competitor whose ultimate goal is to service their OEM accounts first. So if their biggest account drops a huge order on them, they will finish those parts before they get parts for a competitor.
Along with the delivery is quality. The IPC standards for flex PCBs are much different than those for rigid PCBs. So, do they have an IPC certified inspector for flex circuits at their facility?
2. Do they have the equipment to manufacture flexible circuit boards?
As I mentioned above, one can use the same equipment to manufacturer flex circuit boards as is used to manufacture rigid printed circuit boards. However, the level of quality and the ability to control processes is much different.
A few examples:
Etching Equipment – In the old days the saying was “an etcher, is an etcher, is an etcher”, and you could just create work around to use the one piece of equipment for any type of project. With today’s designs, that is just not true.
Dedicated develop-etch-strip lines for flex circuits is a must as thin core flexible materials must be processed on specialized equipment with certain types of rollers along with different chemistries that allow companies to process very tight line and space widths on these circuits.
Flexible PCB During the Etch Process
When trying to process thin core flexible circuit boards on equipment that is designed for rigid PCBs, we have seen panels get wrapped up around rollers, unevenly etched as the panel flexes when the chemistry is sprayed during the process, and in the worst instance, panels fall between the rollers and into equipment which requires the machine to be shut down for repairs.
Coverlay Lamination – When you attach a coverlay to just a flex circuit, it must be done under pressure and at a certain temperature. When manufacturing rigid printed circuit boards, we use multi cavity lamination press to press layers together when producing multilayer(s). While this equipment can be used for coverlay lamination, it is not ideal as it takes too long and is harder to control for this process.
With the invention of a Quickpress, companies can quickly and accurately adhere to the coverlay to the substrate. Quickpresses only press one or two panels at a time so it is easier to control temperature and because of how quickly this process is, which dramatically helps reduce the customer lead time.
Laser Drills/Routers – Typically laser drills are used to drill mirco vias in very high technology printed circuit boards. But what they are also used for is control depth routing and routing of internal patterns on rigid flex circuits as well. When you have a complex design where the flexible PCB that connect the rigid sections is non-conventional shape, we must laminate the flex and rigid sections as complete panels. Then at the end of the process we use a laser cutter to rout away the unwanted material down to the final designs.
This is many time very difficult to do with conventional mechanical routing process as the clearances are usually very minimal.
3. Do they have the in-house engineering and production experience to make sure that the product is manufacturable and that the design is reliable?
Rigid-flex printed circuit boards behave much differently in production and in the final application than rigid printed circuits boards. Delamination at the point where the flex and rigid parts come together are quite common in these designs.
Understanding clearances of the bend radius, the use of Eccobond (where appropriate), the best stiffener material, and other technical details are critically important in assuring that the design is robust.
There is a lot of science that goes into the manufacturing of flex and rigid-flex printed circuit boards and there are companies out there with significant experience in making sure that you get great parts quickly. Unfortunately, there are also companies that are just trying to book business which can make the reliability of your product suspect in the long term.