Printed Circuit Board Reworking
This project is for a plant to upgrade the current PCBs components of a company to more efficient equipment with added functionalities. For the upgrade of the equipment, various workspaces are created which will be capable of accommodating the twenty thousand components and the ten to fifteen operators for the efficient running of the processes. The process followed by the plant will be unpacking, de-soldering, replacing the components, re-soldering, retesting and assigning tags for identification of the packaged components and shipping of the finished components. There are static components in the PCBs which need to be taken good care of to ensure we do not interfere with the working of the finished products. The sensitive parts which are not in the replacement process if damaged will lead to a more costly replacement of the damaged components or the failure of the finished products if not detected earlier. This components should be handled with the right tools and in the right way and arranged well to avoid damage to the equipment.
Process Flow of the Plant
The process flow diagram for the plant includes a un-packaging phase, de-soldering phase, re-soldering phase, retesting phase, identification phase, packing phase and shipment phase. The flow diagram is given in fig 1.The old PCBs reaches the factory and are unpacked by the unpacking machine. The operator tasked with running the unpacking machine will handle the PCBs carefully to avoid breakages of the delicate parts of the PCBs boards. The boards are then secured on the clamps which are on the soldering station which will lead to efficiency in the handling of the plant. The parts on the boards that are to be replaced are identified and de-soldered and consideration have to be made on the points on the board which might be greatly affected by electrostatic discharge, high moistures and high temperatures. The de-soldered parts are then replaced with the upgraded components and then re-soldered.
The re-soldered PCB then moves to the testing place. The designed system will have moving belts controlled by a programmable logic circuit so that once the components passes through one phase it is put on the belt to move to the next stage. At the testing stage, the PCBs are put on the testing board where they will be tested for the electrical requirements. The boards are then passed through an Automatic Optical Inspection Machine for testing on whether the thickness of the layers of the PCBs was affected during the reworking phase. The products will then move to the Identification phase where the PCBs are attached with a sticker for identification indicating that it has been upgraded. The labelling phase we will use programmable Radio Frequency Identification Devices which will record and input the products on the database. The products are then inspected physically to ascertain that all parts are okay and then passed through a counter which also counts and records the completed products on the database. The products are then compared with the ones stored on the database and reconciliation can be done effectively. Defective products are put aside for further testing. The products are then moved to the next stage where they are packed and another sticker attached on the outside box to show that is the upgraded packaged PCBs.
In the plant, most processes are made to run effectively without not necessary requiring that all the operators be very highly trained. The factory design process can be illustrated in the following flow charts and process flow.
The flow chart of the factory process is as follows
The full equipment list for static sensitive area include and tools for operators needed
-The de-soldering iron for removing solder from the original component
-The PLC unpacking and packing machine
-The RFID equipment for identification of finished products
-De-soldering and soldering station
-Counter for counting completed components on the belt drive
-Holding clamp for holding during soldering and de-soldering
-PCB cleaner
-Wave soldering machine
-One Automated Optical Inspection Machine for inspection of disturbance in the layer thickness
-Belt Drive
Cost of each equipment in Great Britain Pounds
The prices of the components was accesses from the Alibaba website on showrooms and electronics and the best equipment chosen based on their performance and cost. .The range of prices was quoted in US dollars thus just converted them using an appropriate exchange rate which in our case approximately 1.8 US dollars make one Great Britain Pound. The components with their costs are given below:
-De-soldering and soldering station of type SL-916D costs 195GBP
-RFID equipment –Programmable RFID NFC sticker costs 0.10 GBP
-PCB cleaner from Skymen JP -060S costs 500GBP
-Soldering iron model 2015 New BAKU Mini Hot Air Soldering iron Anti-Static Soldering station BK-936A costs 20GBP per piece
-Packing PLC and unpacking costs of BT-2000A automatic Packing Machine costs 1000 GBP
-Flying Probe Test Machine cost of Universal electronic testing machine costs 2800GBP
-Automated Optical Inspection Machine will cost 1000GBP
-Wave Soldering Machine costs 1200 GBP on Alibaba from Taian Puhui Electrical Technology
-Soldering wire lead free solder wire copper one ton costs 600GBP
-Silver Soldering paste costs 4GBP per Kilogram
-Belt Drive of model 88 ZA 19 Automotive Driving Timing Belts costs 3GBP per piece
-PLC of type SuperE32 RTU PLC SCADA costs 300GBP per unit
Final equipment cost
-Two de-soldering and soldering station will costs 390 GBP
-22000 RFID equipment costs 2000 GBP
-20-PCB cleaners will cost 10000GBP
-50 pieces of soldering iron costs 1000GBP
-2 Packing PLC and unpacking costs 2000 GBP
-One Flying Probe Test Machine will cost 2800GBP
-One Wave Soldering Machine costs 1200 GBP
-One tonne of soldering wire lead free solder wire copper will cost 600GBP
-30 Kilograms of silver Soldering paste will costs 120GBP
-Automated Optical Inspection Machine will cost 1000GBP
-The electronic soldering area will be a 20 by 50 meters thus the space costs 1000GBP
-20 pieces of Belt Drive will cost 60 GBP
-2 PLCs will cost 600 GBP
Thus the total cost of the equipment’s will be approximately 10000GBP and all the costs were found from Alibaba online websites with availability on January 24th 2016. This component choices is based on the components that can carry out the work effectively and at a slightly lower cost than the other components. This price for the whole process will be approximately 13000GBP including the running costs.
Discussion
The reliability of the products can be greatly affected if the sensitive static components are not handled correctly. This can happen in the case of destruction of some parts of the sensitive PCB board thus hinder connectivity to various components. This can happen in the form of destroying the electrical printed lines on the copper lines which might lead to short-circuiting between components thus would not work well. Also destruction of any equipment or making it loose will lead to component not working well thus affect the reliability of the finished component. The replaced component should be placed in a separate area to avoid the effect of confusing and replacing the original components with the same components.
Physical inspection of soldered joints cannot be used to prove reliability thus joint appearances might not be the best way of determining reliability. Soldering will be done using wave soldering machine instead of hands since wave soldering is good for bulk processes. Soldering at this higher temperatures ensures that there is no electrical disconnect between the components and the wave bump produced afterwards makes the re-soldered components have a very clean spot unlike hand soldering and thus appealing to the customers .The boards are also visually inspected to ensure they meet customers’ requirements, advanced circuit standards and Industry specification. This process will be very important especially when it comes to some omissions that might happen before the final component is packed and shipped. PCBs meeting the acceptable standards are counted, labelled as upgraded and packaged for shipment .Reasons of designing for realiabilty is that it provides margin, mitigates risk from defects and also satifies the buyer components.
For prevention of Electrostatic Discharge(ESD), areas on the PCB which are ESD sensitive will be identified again with the ESD sign drawn during the first fabrication and the whole of the PCB taken as ESD sensitive and protection put on all susceptible parts. Others parts on the PCB that are temperature and moisture sensitive are identified and appropriate care taken.. This sensitive parts of the PCBs are the ones that lead to misfunctioning of the completed component.
The incorporation of programmable logic controllers will be important in the running of the finished components like the SCADA system will monitor flow of the processes.
Conclusion
The main aim of making an assembly plant for the reworking of the PCBs is to reduce cost and increase efficiency of the plant rather than outsourcing all the services. This will lead to flexibility in the completed components since the team modifying the circuitry will be there and measure of the components performance can effectively be deduced from the various testing processes.
For the processes of reworking the circuit boards to be effective, we need to take operators who are keen and robust in the processes. The processes need also a large space for handling the components and avoid equipment congestion and breakages. This will make the processes efficient and great in the implementation and lead to a better reworking phase of the equipment and the above laid down strategies and costs will lead to a better performing system. This designed system will lead to a cheaper and better performance of the reworking the PCBs and thus all the design criteria and planning for the plant have been effectively met. All the processes seem many only for twenty thousand products, it is worth investing in it since the quality of the completed components would not be compromised by anything thus it will fetch the company the best products with a longer lifetime and improved performance.
References
Advanced Circuits Inc, 2009. Building a Printed Circuit Board, s.l.: s.n.
Alibaba, 2016. Alibaba.com. [Online] Available at: http://Alibaba.com/showroom[Accessed 24th January 2016].
Colin, L., 1991. Evidence that Visual Inspection Criteria for Soldered Joints are No Indication of Reliability. Soldering and Surface Mount Technology, 3(3), pp. 19-24.
Keller, J. a. W. J., 1973. The case for unfilled PTH". Electronic Packaging and Production , 13(10), pp. 144-149.
Paquette, J. P. a. B., 2011. Workmanship Risks: Reworking Printed Circuit Board(PCB) Solder Joints. Safety and Mission Assurance Directorate, 18 10.
