Preventing common mistakes in EMS assembly: OptimaTech
The most frequent problems with electronics manufacturing services or EMS assembly are the poor application of solder paste, component alignment, inadequate thermal profiling, and poor-quality control. They can be prevented by standard procedures throughout, correct equipment calibration, operator training, and strict inspection procedures at each stage.
An electronics manufacturing services (EMS) assembly is a process that can be stressful and if one thing goes wrong, all the other things go wrong and it can cost you your business. One faulty component or a bad soldering joint can doom a whole board, or a product that ends up in the field. The tolerance level is becoming smaller and smaller as devices become smaller and more complicated.
The good news? The majority of assembly defects are foreseeable and avoidable. Knowing where they're likely to go wrong allows manufacturers to create safeguards well before the problems get to the production line.
1.Insufficient solder paste application
Solder paste defects are among the major reasons for EMS assembly failures. Excessive paste results in bridging of pads and insufficient paste results in weak or open joints. Both problems are normally caused by either a worn stencil, improper aperture design or inconsistent printer settings.
Prevention: Regularly check and clean stencils, and change them out when they deteriorate. Prevent volume and alignment problems with solder paste inspection (SPI) systems. Keep paste at recommended storage temperature and allow it to come to room temperature before use to ensure the consistency of the paste.
2. Misalignment and placement errors of components
If parts move while you place or reflow, you will get tombstoning, skewing or even missing connections. These problems often result from the programming of a pick-and-place, wear on the nozzle or vibration on the line.
How to avoid it: Regular calibration of pick and place machines and frequent checks of nozzle condition. Ensure that your component libraries are consistent with the parts you're placing. Vision inspection systems can detect alignment issues early, even before the defective board has progressed in the line.
3. Inadequate thermal profiling
The critical point for reflow soldering is the temperature curve. If profile is out, you can get cold joints, lift off parts or damage sensitive parts. Many of these defects are due to using a generic profile rather than a specific one for the board and components.
Prevention: Create an individual thermal profile for each board design and test it using several thermocouples at various locations. Always re-check profiles if changing solder paste, board thickness or component density. Standardized maintenance of the oven helps the heating zones remain stable throughout the time.
4. Failing to do inspections in sequence or in a timely order
Teams under time constraints may not perform full inspections. This is a mistake. The cost to repair a defect when it is caught at assembly is considerably less than the cost to repair a defect after final assembly or in the field.
How to avoid it: Make inspection an integral part of the process, rather than an end. Use automated optical inspection (AOI), as well as SPI and X-ray inspection of concealed joints such as those found under BGAs. Define acceptance criteria well to give a direction to the operators.
5. Moisture-sensitive component damage
There is moisture absorption from the air in many modern components. If water is trapped during the reflow process, it can vaporize and lead to cracking of the package, a defect that is referred to as "popcorning". This damage is frequently not apparent until the part fails.
Prevention: Complying with moisture sensitivity level (MSL) requirements for all components affected. Place sensitive components in dry cabinets, monitor the duration of exposure after opening packages and pre-bake components as required prior to assembly.
6. Lack of documentation and process control
Inconsistent processes can lead to inconsistent results. Where operators use their own memory or informal practice for procedures, rather than written procedures, quality fluctuates from shift to shift and batch to batch.
Prevention: Use clear, current work instructions for each assembly step. Have standardized process documentation and version control, meaning everyone works from the same playbook. Record the operating parameters for the log so that you can pinpoint the cause of any defect.
7. Insufficient operator training
The worst is as bad as bad employees, and the best isn't good enough as long as staff are undertrained. An operator unfamiliar with the process can fail to notice indications, mishandle parts and/or incorrectly set up the process.
How to avoid it: Make investment in structured and continuous training instead of onboarding. Match new operators with experienced mentors; refresh training when processes or equipment change. Promote an attitude of station responsibility for quality.
Conclusion
No one tool or inspection step is the best way to prevent EMS assembly errors; instead, the best defense is a mindset. Defects can be an exception, not a recurring headache when preventative measures are incorporated into your processes, equipment, and team's day-to-day routines.
Begin by taking an inventory of your existing process in the above 7 areas. Know the highest risk areas and then prioritize the highest defect reduction fixes. Small consistent improvements over time will lead to clearly improved yields and reduced costs.
If you are looking for a fine EMS assembly provider, look no further than Optima Technology.
