Electronic manufacturing services (EMS), in the last decade, have witnessed an exceptional rise in accessibility. This rise is like the PCB fabrication service which had evolved in the decade before. This has allowed the possibility of getting EMS for low-volume production and without production commitment. Today we see most of emerging or small-scale companies and even academic institutes getting access to PCB fabrication and PCB assembly.
These EMS are not restricted to large PCBs or through-hole components. The increased access has allowed rapid and small-volume prototyping of PCB design with very small pitch components.
In order to provide a complete end-to-end solution, most of the EMS manufacturers provide the following services:
1. Solder paste application
In this step, the BARE PCB is mechanically fixed between the stencils. Stencil has exposed regions of the components parts which need to be soldered. Once the stencil is fixed on the BARE PCB, then solder paste is applied on the stencil, using applicators that ensure the paste is pulled evenly on all the exposed regions. Solder paste remains on the BARE PCB even after the applicator and stencil are removed.
2. Components placement using pick and place.
Solder paste is applied on the stencil, in the next step it is important to place the components in the right designator location. Component connections need to be aligned with the pads in the PCB in the right orientation and angle. Thus, this process is done using a robotic arm that places the components in the exact position using a miniature vacuum pump. Placement is done as per the XY coordinates provided by the designer. This is usually a sub-file in the Gerber package. Most ECAD software can export in the standard formats accepted by commonly used machines.
3. Solder reflows process.
Components are placed in the designated location then we need to run the PCB with the components through a reflow oven. The reflow oven exposes the completely placed PCB to a specific temperature, which will ensure the solder paste meets its peak temperature and adheres to the BARE PCB.
4. Inspection
Electronic components work on very tight tolerance when it comes to components placement and soldering the margin for error is very small. Often the PCB holding position or component dropping can occur, which can lead to open points or short circuits in the assembled PCB. These issues need to be identified using manual inspection, semi-automatic or automatic inspection.
Manual inspection is possible when the volume is less, and the parts size is on the higher side. This becomes extremely difficult and human error prone when the board size is large, the component count is higher and the size of the components is smaller.
For this semi-automatic or automatic method is preferred, where a reference image for each component is provided from the master board which becomes the golden reference. This is completely automatic, and inspection is image-based, which makes it fast and highly efficient.
5. Functional testing
Assembled PCB consists of multiple points of failure and tolerance ranges that need to be met. This is critical to ensure the PCBA functions as per the desired requirement. To test this dedicated test jigs are built which provided input in the desired range and output can be monitored and the test report is provided. As per the application, PCBA either requires a programming step or not. This is also included in this step.
In case the PCBA fails here, points of failure are identified and sent for rework. Else PCBA is marked QC-cleared and pushed cleaning.
6. Cleaning and dispatch
In production at times, no-clean flux is used, which might leave a residue, which could cause parasitic problems in the long run and might behave differently under different weather conditions. Also, during the reflow process heat residue might exist which might make the PCB look unclean.
Thus, each assembled PCB is passed through a process of IPA cleaning which removes the residue if present and ensures the PCB has a neat and clean look. Thus, making is ready for dispatch.
The major reason to identify and work with a good EMS is to ensure you have a production line that will allow you to mass produce a single design with maximum repeatability. This ensures the production line can be scaled as per the business requirement. Further, the quality ISO documents provided by these vendors allow us to have strong compliance in place.
Most of the leading EMS providers have made their services available online, which allows us to upload the Gerber files online and check the assembly feasibility. This also allows us to get an estimate quickly and generate a cost projection.
To push the clients towards the growing EMS market, most EMS vendors have started accepting low-volume orders as well. This could be as low as 4 or even 2 completely assembled PCB boards. Though the cost can be at a higher end when the volumes are less, and the delivery is expected in a short interval. This becomes more complicated if there is a fund crisis.
In situations like this, it is advisable to have an in-house resource that can provide the assembly of components in-house. This might be complicated if the footprint has a very fine pitch and need special tools for soldering or inspecting the assembled components. Having a well-trained resource for soldering the initial prototype boards allow having a quick turnaround on the prototype boards for low-volume boards.
In-house development of initial prototypes has a range of benefits:
1. Modular testing
Any individual looking at a completed PCB design might find the entire design complex and daunting. However, every PCB design eventually consists of sub-sections that are dependent on each other. When we perform the assembly in-house, we can test the PCB independently block by block. This makes the debugging process extremely straightforward.
2. Verification of components
In initial R&D prototyping, often a new component is introduced. A general practice is to have alternate components. These alternate components ensure that we can swap them and test them out. (It forms an alternate supply chain in case your original component is not available during commercialization.) If we use techniques like hand soldering using either hot air or soldering iron, we can then easily desolder the components and swap them with the alternate components and ensure we are going ahead with the testing.
3. Verification of PCB design
Despite the best efforts put in PCB routing and considering EMI/EMC constraints, getting the first PCB right is very difficult. This gets more complex when RF components are involved. Also, in the rarest cases, design is also prone to human errors. Working internally, allows us to make quick tweaks on the boards using crude techniques such as track breaking or track overlay.
Though it is desirable to have in-house resources to work on the initial prototypes, it comes with a cost. It is mandatory that the lab is equipped with the necessary tools for soldering and de-soldering. If components in the project involve BGA, VQFN, and 0201, then there is a requirement for mini reflow or hot plate. Additionally, you might also require a digital scope for testing the mini signal trace or voltage drops. For low-power signals, it gets more complex as you might need higher resolution voltmeters or ammeters to trace the signal.
Developing this capability in-house might increase the initial capital that is invested, but it provides a higher leverage when it comes to the amount of time required to have a working prototype. Getting the same service from EMS with a very short lead time might make the process expensive, and if the design is at an early stage, there could be uncertainties and eventually lead the prototyping process into jeopardy.
At Lifebound Technologies, we have developed in-house capabilities for research and development in the hardware development space. With our expertise in handling fine-pitch components and PCB assembly, we can provide services for low-volume PCB prototyping for complex designs and projects.
We can be a one-stop location to take your ideas to low-volume production without the burden of coordination with multiple vendors.
You can write to us at info@lifeboundtech.com with your requirements.
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