Key conclusions and analysis of the solderability test report
I. Influence of environmental placement time on the soldering tin adhesion stability of silver-plated boards
This test was carried out in the real environment of the OQC site, simulating the natural placement process of panels in the production scenario. The results show that as the exposure time of the panels increases, the tinning stability index significantly decays from the initial 0.992 (close to the ideal state) to 0.847 (exceeding the stability threshold). This change directly confirms that the parking time of the silver-plated panels in the open environment is the core variable for the attenuation of the tinning performance. Humidity, dust, volatile organic compounds, etc. in the environment will gradually damage the surface activity of the silver-plated layer, resulting in a decrease in the spreading ability of the tin liquid during subsequent welding.
Based on this, it is necessary to strictly control the parking time of silver-plated boards in each production link.
- Specify the transfer time limit for each station (e.g., the process from after pre - treatment to before patching should be completed within 2 hours).
- Designate a closed storage area (control the humidity ≤ 60% and avoid contact with pollutants);
- Establish a "time - performance" traceability mechanism (mandatory re - inspection for overdue panels).
II. The improvement effect of PUMIC treatment on soldering stability
In the test, the solderability of PUMIC-treated boards and non-PUMIC-treated boards was compared.
- The tin wetting stability of the PUMIC board always remains at a high level (meeting the standard requirements).
- The soldering stability of the un-PUMIC board is only 0.449 (far below the qualified line).
The value of the PUMIC process (surface micro-cleaning + etching) is highlighted here: The copper surface of untreated boards is prone to residual organic pollutants (such as grease and flux residues) or inorganic impurities (such as metal dust). These substances will form an "isolating layer" that hinders the wetting of the tin liquid on the copper surface. However, PUMIC removes these interfering layers through physical/chemical means and restores the solderability foundation of the copper surface. This shows that: PUMIC treatment is a necessary means to improve the tinning stability of untreated boards.
III. Comparison of anti-straight plates and the inference that "oxidation is not the main cause"
The test found two key phenomena:
1. The tinning performance of the un - reversed straight board is worse: For the board pieces that have not undergone board surface reversal, due to the long - term contact of local areas with the workbench/air, the accumulation of pollutants is more serious, resulting in the inability of the tin liquid to spread evenly during tinning.
2. Test results of severely oxidized boards: Even when the board shows obvious oxidation (the surface is dark brown), the solderability indicators of the board treated with PUMIC are almost the same as those of the board without PUMIC treatment. This directly refutes the hypothesis that "oxidation is the main cause of the'shrinkage-like poor soldering' at the customer complaint end".
Combined with the conclusion that the solderability is improved after PUMIC treatment, the real cause of the defect points to "non-oxidizing pollutants": substances such as residual grease, dust, and silicone on the copper surface cannot be eliminated through oxidation reactions, but can be effectively removed by the PUMIC process. These pollutants will form a "repellent layer" during soldering, causing the molten tin to shrink (i.e., "tin shrinkage"), which is the core root cause of customer complaints.
IV. Verification of specific issues on the customer complaint board
A special analysis of the circuit boards with the issue of "poor solder wetting" reported by customers shows that:
Wetting time fails to meet the standard: The time from when the molten tin comes into contact with the board to when it is fully spread exceeds the upper limit of the standard (for example, the standard requires ≤ 2 seconds, but the actual time is 3.5 seconds).
Insufficient soldering tin stability: The thickness of the tin layer fluctuates greatly (range ≥ 0.1mm), and "cold solder joint" marks appear at the edges.
Neither of the two indicators meets the enterprise standards, which directly verifies that "the defect in the tin - wetting performance of the board itself" is the main cause of the customer complaints, rather than the soldering process problem at the client side.
Attachment information
- Screenshots of the testing process: 23se.JPG, 23se1.JPG (showing the placement scenario of the board components and their appearance after tinning);
- Compressed package of the full report: Soldering test report.rar (Creation time: July 26, 2008, 15:21:25; Size: 334 KB; Download times: 0).