SMT factories have an important quality assessment index for production, which is First Pass Yield(FPY). FPY meaning is from beginning production to end process first pass ratio. The parameter reflects on manufacturing and quality control capacity of SMT factory, FPY higher, relative capacity higher. Now, this industry pursues an aim is less than 100 ppm, that is 1 million productions, quality issues less than 100 pieces. Of course, this aim is set like NOKIA, LG company. Generally, huge experience smaller factories can reach 97% to 98% FPY.
That is needed more time if you want to know details factors that could involve so-called: human, machine, material, method, and environment. So, in this article, we only pick up some important factors to develop.
We know an electronics appliance can work finally, have two key points, one is components quality is ok, and two is it right connecting. Whether PCB or mount, all is provided support to among components contact, and finished suitable connecting. SMT factory reassures mainly components’ pin and PCBs pad connecting through solder. Of course, the soldering’s premise is the right components in the right location at PCB.
If we want to improve FPY, have two things to work on. First is assured component quality, solder paste, and various other materials’ quality. Others are the whole process has strong measures to assure manufacturing quality. So, this isn’t easy work, have many uncontrolled and unexpected factors, that have big challenges for supervisors too.
we know manufacturing electronics finished has many processes, so assure FPY isn’t only dependent on inspection equipment although it is very important, but also must emphasize other factors. More precisely， it is a serial data model, the result of the continuous action of multiple links. Any defects in this link will lead to a failure to finish products.
Somebody said good product is designed. I reckon it makes sense. If have not considered multiple detail factors at the beginning of design, that will lead to a huge influence on manufacturing even terrible things. For example, the line width and line spacing in the pcb design, and the manufacturability requirements on the smt, if the drawing you design does not meet this line spacing, it will be a great trouble for the subsequent production, and there will be a great hidden quality risk. There are countless problems that can be said to be difficult to guarantee the quality of the poor design, so it makes sense that the salary of good designers and experienced designers is also very high.
How to realize the reliability of welding involves many links. For example, the pcb cannot be oxidized, and the pin of the component cannot be oxidized, so the QC is received from the raw material supplier, and the tin test is performed on the pcb and the pin of the component. Of course, the storage conditions of the inventory are also very important. The warehouse needs to have appropriate storage temperature conditions to ensure the quality of components. Solder paste is generally refrigerated, and it must be warmed up in advance before production. If there is not enough time to warm up (2-4 hours), the moisture in the air will condense in the solder paste. During reflow soldering, the water vapor will fry. flying components.
There are many issues related to equipment, such as the temperature of reflow soldering, the adjustment of the placement machine, the adjustment of the printing machine, etc. are all factors that affect the quality. For example, the frequency of stencil wiping, different packages (pin density, residual solder paste tolerance), and different pcb quality (high consistency of pcb solder mask layer) require different wiping frequencies. Of course, the placement machine must be 100% correct, which is the premise. Guarantee the position and quantity of solder paste, give up manual printing and semi-automatic printing machines; ensure that the machine is stable, the furnace temperature and solder paste are suitable, there are too many links, and there are too many things to say.
Although AOI cannot guarantee the completion of detection 100%, it will greatly improve the detection efficiency. Even for experienced engineers, no matter how many PCBs are soldered, as long as they are hand-soldered, there may be defective products. The same is true for visual inspection. Manually looking at hundreds of PCBs can not guarantee 100% quality. Through AOI detection, after the machine alarms, manual inspection will greatly improve the detection efficiency.
Now, SMT industry is inclining forward infer quality issues, rather than AOI assure quality. We can do it, that is assure and improve continuously process, don’t add mess to the customer, design defects by improving the process to fix. AOI, SPI, etc equipment is only the process control a section.
Finally, reached a conclusion: assure quality, need to backward infer from end to begin, keep analysis, keep improve stability, this is an interactive process. In one word, the result does not result, is the process’s result. The key point is process control. All results have their cause, we must catch the cause and can keep the final result.