Have you considered how the PCB design rules and Gap-Ratio affects your manufacturability and soldering process efficiency?
Main Takeaways:
- Boost Solderability by Up to 50%: Optimizing the hole size in Through-Hole Technology (THT) significantly enhances solder fill.
- Enhance Process Robustness: Increasing the Gap-Ratio improves heat transfer, leading to more reliable soldering processes.
- Reduce Manufacturing Costs: Optimized THT-hole dimensions can cut cycle times and energy consumption, lowering costs.
- Expert Assistance Available: Contact our company to implement these optimizations in your manufacturing processes.
Why worry about solder joint design rules?
In the dynamic world of electronics manufacturing, the push for higher functional integration and stringent reliability standards drives increasingly complex printed circuit board (PCB) designs. Integrating both Surface Mount Technology (SMT) and Through-Hole Technology (THT) components presents unique challenges, particularly in achieving high-quality solder joints during selective wave soldering processes [1].
This article delves into how optimizing THT-hole dimensions can dramatically improve solderability and reduce manufacturing effort by up to 50%. By adjusting the gap between the component pin and the PCB hole—known as the Gap-Ratio—we can enhance heat transfer, bolster process robustness, and streamline production efficiency.
The Challenge of Selective Wave Soldering in Complex PCBs
Selective wave soldering is a preferred method for soldering THT components on mixed SMT/THT boards, as it minimizes thermal stress on sensitive components and the PCB. However, as PCBs evolve to include more layers and higher copper content to meet performance demands, manufacturers encounter several hurdles:
- Insufficient Hole Fill: Thick PCBs with substantial copper layers and high thermal mass components dissipate heat rapidly, preventing solder from adequately filling the through-hole.
- Thermal Mismatch: Discrepancies between the heat required by the solder joints on the PCB layout and energy supply during soldering can lead to defects, compromising solder joint reliability.
- Manufacturing Bottlenecks: To compensate for poor hole fill, manufacturers may increase preheat temperatures and soldering times, risking thermal damage to components and reducing production efficiency.
Looking into a THT solder joint, the hole fill is affected by the copper layer design, the process parameters e.g. preheat temperature, solder temperature and solder contact time.
Standard Hole Dimensioning in PCB design rules
The hole fill is dramatically sensitive to the PCB thickness as the thermal demand increases disproportionally. Nevertheless, current footprint libraries are usually defined with a fixed gap. For the sake of manufacturability the PCB thickness must not be neglected when dimensioning PTH.
Understanding the Gap-Ratio
The Gap-Ratio is a crucial parameter in THT-hole dimensioning. This concept has been adopted in DIN EN IEC 61188-6-3. It is defined as the ratio of the gap width (the difference between hole diameter and pin diameter) to the PCB thickness:
Where:
- D: Hole diameter
- d: Pin diameter
- l_PCB: PCB thickness
An optimized Gap-Ratio facilitates better solder flow and heat transfer, resulting in improved hole fill, better process robustness and larger process windows.
The Study: Assessing the Impact of Hole Dimensioning
A comprehensive study was conducted to evaluate how THT-hole dimensioning affects solderability in selective wave soldering using a test PCB Layout.
PCB Design and Experimental Setup
- PCB Specifications: A 6-layer PCB with a thickness of 1.6 mm was used. Hole diameters varied from 0.9 mm to 1.6 mm, while the pin diameter remained constant at 0.6 mm.
- Gap-Ratio Variation: The Gap-Ratio ranged from 19% to 63% by adjusting the hole diameter.
- Process Parameters: Preheating temperatures were set at 80°C, 100°C, and 120°C. Soldering contact times were 2 seconds and 5 seconds.
- Evaluation Metrics: Hole fill percentages were measured using X-ray inspection. Process robustness was evaluated based on consistency across different copper layer designs and process parameters.
Key Findings: Larger Holes are way better
1. Improved Solderability
The study revealed a clear correlation between increased Gap-Ratio and enhanced hole fill:
- Significant Hole Fill Improvement: Larger hole diameters resulted in better hole fill, achieving compliance with IPC-A-610 [4] standards without the need to increase preheat temperatures or soldering times.
- Enhanced Heat Transfer: A larger gap allowed more solder to flow into the hole, improving heat transfer and ensuring the solder remained molten long enough to fill the hole completely.
The figure shows how the improvement of hole fill primarily over Gap-Ratio rather that due to preheat temperatures or solder contact time.
Enhanced Process Robustness and Reliability
- Reduced Sensitivity to Variations: The soldering process became less sensitive to changes in preheat temperature and soldering time, leading to more consistent results.
- Adaptability to Complex PCB Designs: Even with challenging copper layer configurations, an optimized Gap-Ratio improved solder joint quality.
Reduced Manufacturing Costs
- Cycle Time Reduction: Improved hole fill at lower temperatures and shorter soldering times enabled a reduction in cycle times by up to 50%.
- Energy Savings: Lower preheat temperatures and reduced soldering times decreased energy consumption.
- Minimized Rework: Enhanced first-pass yield due to better hole fill reduced the need for costly rework.
- Improved automatability: Automated placement of THT pins in to larger holes is easier and requires less expensive equipment.
Improved on Life Time and Reliability of Components:
- Reduced thermal damage: Lower temperatures and contact times lead to significantly lower thermal stress load for the PCB and the components.
- Longer life time and reliability: Avoiding thermal degradation of component and PCB materials leads to longer lasting electronic modules with higher reliability.
- Less Material wear: Reduced risk of copper dissolution and delamination endangering the functionality of the electronic module.
The capillary action truth:
It is common sense that capillary action is an important physical driving force in the gap between pin and PTH. Taking the results of this study serious means that this is a complete misconception. Physics says, that the capillary action decreases as the gap increases. As we have shown, that the increased gap significantly improves the solder hole fill, the common sense can simply not hold true.
This has been told over and over again (possibly also for the sake of descriptiveness) but that does not make it true.
Manufacturing Implications
By optimizing THT-hole dimensions, manufacturers can:
- Enhance Product Quality: Achieve higher solder joint reliability and meet industry standards.
- Increase Process Efficiency: Reduce cycle times and energy usage, boosting throughput.
- Lower Production Costs: Minimize rework and scrap, reducing overall manufacturing expenses.
Manufacturing Implications
By optimizing THT-hole dimensions, manufacturers can:
- Enhance Product Quality: Achieve higher solder joint reliability and meet industry standards.
- Increase Process Efficiency: Reduce cycle times and energy usage, boosting throughput.
- Lower Production Costs: Minimize rework and scrap, reducing overall manufacturing expenses.
Conclusion
Optimizing THT-hole dimensioning by increasing the Gap-Ratio offers a substantial opportunity to improve solderability and reduce manufacturing costs in selective wave soldering processes. Our extensive experience in optimizing PCB layouts and further soldering studies on wave soldering and multi-wave soldering confirms that considering the Gap-Ratio early in the design phase leads to better manufacturing outcomes.
The study demonstrates that:
- Solderability Can Improve by Up to 50%: Without additional thermal stress, better hole fill is achievable.
- Process Robustness Is Enhanced: Reliable and consistent production outcomes are attainable.
- Manufacturing Costs Can Be Reduced: Cycle times and energy consumption can be significantly lowered.
Implementing these findings allows manufacturers to elevate product quality, shorten time-to-market, and gain a competitive edge in the electronics industry.
Have you considered how the PCB Layout and Gap-Ratio affects your manufacturability and soldering process efficiency?
Are you looking to enhance your selective wave soldering processes and achieve significant cost savings? Our company specializes in optimizing PCB manufacturing and soldering techniques. With our expertise, you can leverage Gap-Ratio optimization to improve solderability and process efficiency.
Contact us today to discover how we can assist you in transforming your manufacturing processes and delivering superior quality products to your customers.
Read more on Gap-Ratio on the SIEMENS Blog
References
[1] R. Seidel, T. Ahrens, J. Friedrich, A. Reinhardt, and J. Franke, “Experimental identification and prioritization of design and process parameters on hole fill in mini wave soldering,” Microelectronics Reliability, vol. 131, p. 114497, 2022, doi: 10.1016/j.microrel.2022.114497.
[2] R. Seidel, C. Kästle, M. Ockel, and J. Franke, “Impact of THT-hole dimensioning on manufacturability in selective wave soldering,” Microelectronics Reliability, vol. 137, p. 114773, 2022, doi: 10.1016/j.microrel.2022.114773.
[3] R. Seidel, “Modellbasierte Optimierung des Selektivwellenlötprozesses,” 2023.
[4] Abnahmekriterien für elektronische Baugruppen: Genehmigt als Amerikanische Nationale Norm durch das American National Standard Institute (ANSI) am 10. Mai 1995 ; ANSI/IPC A 610, Revision B, Dezember 1994, einschliesslich Amendmet 1, Januar 1996 ; (FED-70-04) = Acceptability of electronic assemblies, IPC-A-610E, IPC – Association Connecting Electronics Industries, Berlin.
Keywords: Selective wave soldering, THT-hole dimensioning, Gap-Ratio, PCB manufacturing, solderability improvement, process robustness, manufacturing cost reduction, electronics assembly, PCB design optimization, through-hole technology.