|
7 October 2026
Poor yield on a PCB assembly is rarely down to one issue. In many cases, several parts of the design and manufacturing process are working against each other.
That was the situation when J-TEQ began working with a major customer in a highly regulated technology sector in 2024. The PCBA had a historical manufacturing yield of around 50%, and there was no obvious single cause.
Our initial assessment pointed to several contributing factors, including the PCB’s thermal characteristics, connector design, solder paste deposition, and the mechanical forces introduced during assembly.
Working alongside the customer and Mike Cummings of TSI Consultants Ltd, we reviewed the full manufacturing process and tested potential improvements through controlled trial builds.
Across two principal trial builds, we identified and addressed four key areas, increasing manufacturing yield from approximately 50% to 95%.
Our customer's assembly presented a series of manufacturing challenges, rather than an isolated fault. These included:
Some of these issues could be addressed through manufacturing process changes, but others were influenced by the underlying PCB and component design. This limited how far the process could be optimised without rolling out design changes.
We used the trial builds to investigate how each production stage was affecting the final assembly and identify where controlled process changes could improve repeatability.
One of the first areas we reviewed was the reflow process. We found that the PCB contained substantial ground-plane areas and variations in thermal mass. These issues meant the conventional ramp-to-peak profile was not transferring enough thermal energy to certain parts of the board early enough in the reflow cycle.
As a result, different areas of the PCB responded differently to the same thermal profile, making repeatable soldering more challenging.
We reviewed the assembly’s thermal characteristics before developing a modified reflow profile, this time with a more aggressive temperature increase through the initial oven zones. This provided additional thermal energy earlier in the process, helping areas with greater thermal mass reach the required temperatures more consistently.
Our revised profile improved thermal balance across the assembly, supporting more consistent solder-joint formation. It showed that the reflow profile needed to reflect the PCB’s actual thermal characteristics, rather than follow a standard profile.
Our investigation identified a second issue at specific connector locations on the PCBA. The connectors used an unusual pin configuration, and the existing stencil design was not depositing enough solder paste to achieve the required solder volume. This created a risk of weaker solder fillets and reduced mechanical strength at these locations.
To address this, our team reviewed the relationship between connector geometry, stencil aperture design, solder paste volume, and solder-joint formation. We then introduced a controlled solder paste overprinting process to provide extra solder to affected locations.
By increasing solder volume, we produced a more robust solder connection at key connector points. These changes also showed how stencil design and solder paste deposition can be adjusted to accommodate components with more complex geometries.
Another source of process variation we identified was connector deformation. Any exposure to reflow temperatures could cause movement within the connector body, which in turn could affect its geometry while solder joints were being formed.
We reviewed the connector's behaviour throughout the thermal cycle before introducing temporary mechanical support during reflow. This helped the connector maintain its intended geometry while the solder joints were formed. We then removed the temporary support after reflow.
The temporary support reduced connector deformation during reflow and improved repeatability across the assembly process. It also reduced the potential for defects caused by connector movement and resulting mechanical loading on the solder joints.
The last area we looked at was inserting devices into the connectors after soldering. The insertion force required at this stage could be transferred through the connector body into the soldered terminations, placing mechanical stress on the solder joints.
Our team developed a controlled method to reduce friction during insertion, lowering the force required and reducing mechanical load on the connector and associated solder joints.
The revised process made component insertion more controlled and repeatable while reducing mechanical stress on the connector assembly and solder joints. By lowering insertion forces, it also reduced the load transferred through the connector body into the soldered terminations, helping protect the integrity of the solder joints.
Our four improvements reduced process variation and created a more controlled and repeatable manufacturing process for our customer.
| Initial Manufacturing Yield | Yield After Optimisation |
|---|---|
| ~50% | ~95% |
Together, these improvements increased manufacturing yield by approximately 45 percentage points across two principal trial-build cycles.
The project also helped us distinguish between issues that could be addressed through process optimisation and those linked more closely to PCB design, components, and mechanical interfaces.
Manufacturing process improvements can help accommodate more challenging product designs. However, the design itself can still restrict the available process window and limit how far manufacturing performance can be optimised.
Areas such as PCB layout, thermal behaviour, component geometry, and mechanical interfaces can all create manufacturing constraints. Design for Manufacture (DFM) helps identify and address these issues earlier, supporting a wider process window and more repeatable production.
Our team continues to work with this customer on further process improvements alongside recommendations for potential DFM changes. We aim to establish a wider and more repeatable manufacturing process window, supporting:
This project demonstrates how process engineering, controlled trial builds, and practical manufacturing experience can improve the production of a challenging PCB assembly.
By reviewing the full manufacturing process, we identified the factors contributing to poor yield and introduced targeted improvements that increased yield from approximately 50% to 95%. The changes we implemented helped establish a more robust and repeatable process for ongoing production.
Experiencing manufacturing yield or repeatability issues with an existing PCB assembly? Talk to J-TEQ about process optimisation and DFM support.
