A 0.3% Temperature Anomaly Traced to a Microscopic Solder Joint
Jul 21,2026
During the production of an active neurosurgical device, we encountered an intermittent temperature-rise anomaly with an occurrence rate of approximately 0.3%.
What made the issue particularly challenging was that every product underwent 100% in-process inspection, followed by sampling inspection at final testing, yet conventional testing methods could not reliably detect the anomaly. Initial disassembly and inspection of the affected products also revealed no obvious defects.
Faced with this low-frequency and difficult-to-reproduce issue, the Diagsensor engineering team systematically examined each potential contributing factor and conducted multiple rounds of comparative testing.
The investigation ultimately traced the problem to a small solder joint inside the product.
Under static conditions, the solder joint functioned normally, making the issue difficult to detect through conventional testing. However, when the product was moved or flexed, mechanical stress could cause intermittent contact at the solder joint. This disrupted temperature signal detection and ultimately resulted in abnormal temperature-rise behavior.
Identifying the root cause was only the first step.
After detailed discussions with the customer, we implemented improvements in two areas: reducing the probability of occurrence and improving defect detection.
1. Improved Solder Joint Protection
Under the original process, the solder joint had no additional mechanical protection. We added heat-shrink tubing to protect the joint and reduce the effects of pulling, bending, and mechanical stress during assembly and product use.
2. Enhanced Testing Method
The original test primarily determined whether the product could reach the target temperature, without monitoring the complete heating process.
We therefore introduced temperature-rise curve testing. Instead of evaluating only whether the final temperature met the acceptance criteria, the updated method monitors the entire heating profile, making potential abnormalities easier to identify.
Following implementation, the relevant process parameters, solder joint protection method, and testing requirements were incorporated into the Work Instruction (WI). The effectiveness of these improvements was then continuously verified through subsequent production samples.
In medical device OEM manufacturing, resolving a problem is not the most difficult part. What truly matters is the ability to investigate even a 0.3% intermittent failure, identify its underlying mechanism, verify the root cause, implement effective improvements, and establish a closed-loop manufacturing process.
By doing so, an isolated issue becomes repeatable and transferable manufacturing knowledge.
This is how we define the value of engineering and manufacturing at Diagsensor.
Jul 21,2026
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