How to choose a pcb assembler or pcba manufacturer is often a question I receive from readers. When performing electronic product development activity, PCBA is often an important source of quality issue, hence choosing the right partner for this important operation of assembling components onto pcb is critical.
0./ Do they have clear established processes
This is the most important in every factories and in every companies to avoid mistake and to achieve repeatability over production process : having a clear and efficient operation manual and training.
Several years in China where I observed resources are a bit unstable made me realize that processes and training are at the core of every company who success. You can hardly trust resources but you can trust processes and training making the company less dependent to employees and resources.
For this reason, having a solid operation manual, mature quality management process and well established training for new comers is very important. If your supplier doesn't have this, then get prepare for uncertainty.
1./ How are their machines (pick and place and reflow oven)
Old, new, what is their accuracy, how many feeder can they handle, are they Chinese or Japanese machines.
Those parameters are important because it can influence productivity and yield.
If machines are not very accurate then they will not be able to handle placement of the smallest components with tiny footprint package such as 0201 smd type.
Some old machines not being properly maintained and used for production may for example slow down the production due to defectives generation. If for example the pick and place machine is not accurate enough or if it gets constantly break down then the production will slow down one way or another because your manufacturer will not be able to ensure a continuous manufacturing flow.
I have seen in the past some pcb assemblers having constantly their machine breakdown, leading to have several production being delayed because they were uncapable to make their work.
I have also seen some wannabee pcb assembler buying some second hand machine who would not place components accurately at the right x/y position. Operators will then need to place back the component by hand, leading to increased production time and production delays. Only having one components to put back manually by hand on a PCB over a 10 000 pieces PCB made can lead to a very long delay.
2./ What kind of quality inspection do they implement
Everybody knows that quality control in China is crucial when condering manufacturing operation. For pcb assembly operations there are mostly 2-3 quality control operations which are implemented but not all suppliers implements them all.
- VISUAL BY HUMAN: First there is visual observation to verify if components are properly soldered, this is made by operators most often and tend to spot any abnormal components configurations. This one is absolutely A MUST in every factory which produce product.
- VISUAL BY MACHINE: Second, to accelerate the previous process of visual quality control and to make it more reliable Automated Optical Quality Control can be implemented. Typically this is a machine which using a camera will compare by using visual recognition the presence of the right component at the right location on the pcb. It is typically making picture comparison.
- FUNCTIONAL TEST: Function test is performed to verify if pcb is able to function the way it should. This is usually done by powering the pcb, by generating input and by observing and analyzing output generated by PCB.
3./ How many production lines do they have
If you have important volume to manufacture and are in rush on delivery then, how fast can they produce is essential. If they have several orders to manage in the same time, then having several lines running simultaneously is an advantage to ensure they would be able to handle faster all those orders by running some productions in parallel.
Choose your PCB partner making sure they have some back up plan in case they get overbooked
4./ Do they have stock for standard passive components
Most of time pcb assemblers will maintain some stock of common components such as resistors, capacitors, diode, transistors, inductors. This can be useful in order to avoid having to supply them by yourself and to maintain inventory counting.
The diversity of components for those passive make that you may have to buy many different SKU and as they mostly sell by MOQ of 4000-5000 pieces in reel, you may remain with unnecessary one, hence better having your PCBA manufacturer to handle this cost for extra component.
5./ Do they accept small orders
Before launching any mass production you will need to make some PCBA prototype, which is equal to make some very small production. You need to do this before taking the risk to launch an unstable product.
You could as well work with two different suppliers : one for prototype and one for mass production but I don't recommend it because of consistency in the process flow. It is always better to have a continuity between product development phase and manufacturing phase. So, you better make sure they are capable to make some small run and not only big ones so that they will be able to follow up on production later on.
6./ How do they apply solder paste
Is it made manually or automatically with a machine? Because human mistakes are usually in higher rate than machine mistakes, it is better to use a pcb assembler having an automatic or semi automatic machine.
An operator depositing solder paste by hand can without noticing it slightly slide the solder paste net and deposit solder paste on wrong position pad leading to short circuit.
Machines, as long as properly maintained (calibration) are repeatable.
7./ Does their workers are qualified for hand placement
Sometimes, a particular type of components can not be placed using pick and place machine (for example if the components has a very particular shape making that suction head can not grab it, or if the components is not sold in reel or tray), then an operator will have to place the component manually on the pcb pad before reflow.
You need to make sure those operators have proper training to do so and they can do it even for tiny components. Sometimes components are so small that it really requires to have proper skills (and a microcsope) to place them properly.
8./ Do they separate lead and non lead production lines
If your pcb assembler is using solder with lead for a particular market (as it is usually cheaper to use soldering with lead) and if you are requiring lead free soldering then you need to make sure they properly don't mix both.
Serious pcb assemblers will have physically separated production lines so that even lead dust would contaminate lead free production. I have seen some pcb manufacturers separating production line by wall or by nets.
9./ What is their defective rate
How many pcb over 100 produced do they have to rework after production. The yield is an important consideration because it indirectly affect the delivery time.
Most of supplier will tell you they have less than 1% defective but the reality is often well different. Makes sure of what this rate is.
10./ How do they store materials
China has humidity in the air and it is sometimes quite hot out there. When you get delivered components or pcb you will notice they are usually vacuum sealed and their packages contain silica gel to remove humidity. There is a reason for it : oxydation.
Yes, printed circuit board and components pads can oxydate with air and humidity, making that you can not use them easily later on when you have to solder them again.
Make sure your pcb assemblers close properly in a sealed package the remaining unused components and pcb after production, so that you can use them for next production.
I hope this article from the ground will help you.