There are several problems OEMs face when trying to find the resources for PCB rework on a mass scale when electronic goods are being recalled. The capacity for large scale PCB rework projects, which heretofore have primarily required manual labor, is limited in some geographic areas where all of the largescale PCB assemblers have moved off shore. First of all the processes for rework require a different skill set than original PCB assembly. Secondly, those companies having lots of engineering resources dedicated to the original manufacturing processes are not necessarily highly experienced in PCB rework. Thirdly, automated equipment can produce original assemblies at a high rate of speed and with consistent quality. This is not the case for rework that in many cases is highly dependent on manual workmanship. One of the other problems is that this original production capacity , which in many cases is the same capacity for PCB rework, is located far from the OEM’s main markets and therefore requires extra time in shipping the items back and forth.
There are several options available for original equipment vendors when electronics-related large recall projects come up. These options include but are not limited to
1. Scrapping the assembly or subassembly
The “starting over” option when there is a lot of material to be reworked is attractive in several cases. In situations where the cost of the rework, factoring in the yield, is 50 per cent or more of the marginal cost of a “new” assembly, scrapping the material makes the most economic sense. There are product recall cases where some of the components found in a new assembly are not available in a timely fashion thereby making the rework of boards a viable option.
2. Send Items Back for Rework to Lower Wage Countries
Sending the assemblies back to a low wage country where the item was originally produced makes sense in some product recall scenarios. The process for the assembly as well as any fixturing for putting the assembly together will be known by the original builder. This may speed up the process as the “learning curve” will only be there for disassembly. Another reason for sending it back to the low wage country of origin is that the OEM has the greatest leverage with the original manufacturer of the product. The producer may simply have to take the ”good” (Originally assembly work) with the “bad” (rework). Getting another vendor to learn your product, develop the processes and duplicate fixtures may take too long a period of time if a rework project developes. Many manufacturers are really good at PCB and final equipment assembly, but may just not have the expertise or the equipment to “undo” the assembly and rework the PCBs.
3. Hire temp staff in your facility
Another option, depending on the complexity of the rework, may be to add “temp” staff to your own manufacturing or assembly resources. If the rework involves the simple replacement of a fuse or a pushbutton and some wiring this might be an option in dealing with the product recall. If it involves the rework of a medium or fine pitched device on the PCB this may not be a viable option and more expertise must be needed on the rework project. Assuring consistent outgoing quality levels may be difficult in these cases.
4. Hire resources in the US-contract rework and repair houses
Another option is to hire a contract rework and repair services company. These companies have skilled soldering technicians for hire who can handle complex projects. However, in many cases they do not have the manpower to get through projects where there are tens of thousands of devices needing replacement. These companies, while having a skilled workforce and professional tooling , have limited capacity. When very large electronics-related recall projects are at hand, their manual processes are limited by personnel capacity. In order for these service providers to have a stepped increase in capacity, time, a precious commodity in PCB rework, is required.
5. Vendor with semi-automated PCB Rework capabilities
Some larger or more experienced assembly or PCB rework companies are beginning to build some automated capacity for the previously all manual PCB rework and repair processes. Some of the previous manual processes, which can be automated, include board solder excavation and site preparation, solder paste dispensing and device placement, post reflow optical and x-ray inspection. These processes, once automated, can be faster and more consistent in their outcomes compared to their manual counterparts.
There are several PCB rework process steps which can be automated to some degree in order to get a faster turn, lower cost rework project. For device removal, assuming the PCB and the parts populated on the board can handle the reflow temperatures, a robotic solder excavation tool can “prep” the board prior to device placement. The solder excavation tool, now found on several high end rework systems, can be programmed and taught to perform the hot air, non-contact solder excavation (Figure 1) . The nozzle, sized to the pads or area requiring excavation, can be driven from point to point heating up and reflowing the solder to a liquidus condition and then with the integral vacuum source , extract the molten solder. On the solder paste or paste flux dispensing processes, a programmable XY gantry robot can dip or dispense solder paste or flux. This controls the location and volume of the solder materials. This is then by the devices being placed by a high speed gantry system (Figure 2).
After reflow automatic inspection can speed up the rework process and lead to better outgoing quality levels. Automated optical inspection (AOI) (Figure 3) and Automated X-Ray Inspection.
Figure 4- Automated Optical Inspection
(AXI) (Figure 4) can both help insure higher outgoing quality levels. With manual inspection being only 80% effective at best, these post reflow inspection tools eliminate the throughput “bottle neck” awhile leading to more consistent results.
Many of the high volume electronics recall capacity challenges can be overcome with a vendor base employing the latest in semi-automated PCB rework equipment, having the skill set and experience for engineering the processes and the skilled soldering and rework staff in the latest IPC7711/21 PCB rework and repair standards.
Bob is the principal at BEST Inc., a contract rework and repair company, and BESTProto, a prototype PCB assembly business, located in Chicago, IL. He is an IPC master instructor and has been speaking and writing for the PCB rework/repair and assembly industry for over 15 years. Bob was awarded an electrical engineering degree from the University of Illinois and also holds an MBA from DePaul University. He holds patents in surface science, electrical controls and electronics rework.