In the design of renewable energy inverters (such as photovoltaic and energy storage systems), power density and long-term reliability are the two core pillars that determine success or failure. As grid-connected and safety compliance engineers, we understand that in systems routinely handling hundreds of volts and thousands of amperes, the failure of any single connection point can trigger a chain reaction, leading to system shutdowns, costly on-site repairs, or even catastrophic safety incidents. Therefore, although surface-mount technology (SMT) has become mainstream, THT/through-hole soldering remains an indispensable core process in high-voltage, high-current power-stage circuits due to its unparalleled mechanical strength and electrical reliability. It is far more than a simple component fixation method-it is the cornerstone that ensures inverters can operate stably for over twenty years under harsh outdoor conditions, extreme temperature and humidity cycles, and continuous mechanical vibrations.

This article will delve into the critical role of THT/through-hole soldering in modern inverter PCB design and manufacturing. It will analyze in detail how it addresses the extreme electrical and thermodynamic challenges posed by busbars and high-current terminals, and explore how it synergizes with advanced thermal management, EMI suppression strategies, and full-lifecycle traceability systems to ultimately achieve efficient, safe, and reliable energy conversion.

Busbars and Terminals: The Physics Behind THT Soldering in Power Connections

The heart of a renewable energy inverter lies in its power-stage circuit, which efficiently converts DC electricity into grid-compatible AC electricity. The currents involved in this process are magnitudes larger than those in consumer electronics. These high currents must be transmitted losslessly through robust busbars and heavy-duty terminals, both inside and outside the PCB. Unlike SMT solder joints, which form connections only on the PCB surface, THT/through-hole soldering involves inserting component leads through plated through-holes (PTHs) in the PCB. Molten solder forms robust joints on both sides of the PCB while achieving a 360-degree metallurgical bond along the hole walls. This structure, akin to reinforced concrete in construction, provides exceptional resistance to vibration and mechanical stress, making it the only reliable choice for securing heavy power components such as large inductors, filter capacitors, and IGBT modules.

The advantages and disadvantages of this connection method are directly reflected in two key physical parameters: contact resistance and thermal rise.

1. Minimizing Contact Resistance: A high-quality THT solder joint can achieve contact resistance as low as micro-ohms (μΩ). This is due to its vast contact area and gap-free metallurgical bond, effectively preventing resistance increases caused by microscopic poor contact or long-term oxidation. Consider a simple calculation: If a connection point carries 500A of current and its contact resistance is just 1 milliohm (mΩ) higher than the ideal state, the power formula P = I²R reveals that this point will generate 500² × 0.001 = 250 watts of excess heat. This not only represents significant energy waste-potentially reducing system efficiency by several percentage points-but also creates a dangerous hotspot that could lead to solder joint melting, PCB substrate carbonization, and ultimately, fire hazards.
2. Effective Control of Temperature Rise: Low contact resistance directly results in low temperature rise. During the initial design phase, especially in the NPI EVT/DVT/PVT (New Product Introduction Engineering/Design/Production Validation) stages, we must conduct detailed thermal simulations (CFD) and mechanical stress analyses (FEA) for every critical THT connection structure. This is not just theoretical calculation but also requires building prototypes during the DVT phase and performing actual measurements using thermal imaging under full load, overload, and even short-circuit conditions to ensure the temperature rise remains within the design margin. This is particularly important for applications involving Heavy Copper PCB. Thick copper layers (e.g., 6oz or higher) can carry high currents but also act like massive heat sinks, rapidly drawing away heat during soldering, making it difficult for the solder in the holes to fully melt. This places extremely high demands on the energy input and heat management of the soldering process; otherwise, "cold solder joints" or incomplete fillings may occur, creating long-term failure risks.

Crimping and Soldering Synergy: The Art of Building a High-Reliability Process Window

In power module assembly, crimping and soldering are the two mainstream connection technologies. Crimping uses mechanical force to tightly bond terminals and wires, offering speed and no need for heating, but its long-term reliability heavily depends on precise tools and perfect matching of terminal and wire specifications. Any minor deviation, such as tool wear, wire diameter tolerance, or operator technique variations, can lead to insufficient or excessive crimping force. The former causes poor contact and increased resistance, while the latter damages the wire, reducing its fatigue resistance. Over time, material creep effects may also reduce crimping force, especially after frequent thermal cycling.

In contrast, THT/through-hole soldering provides a more stable and predictable metallurgical bond. The intermetallic compound (IMC) layer formed between the solder, pins, and hole-wall copper ensures permanent and electrically stable connections. In fields where reliability is paramount (e.g., aerospace, high-end industrial control), we even adopt a "crimping + soldering" redundancy strategy: crimping ensures mechanical fixation and preliminary electrical connection, while soldering forms an airtight, low-resistance permanent electrical pathway to guarantee fail-safe connectivity.

Defining and strictly controlling the soldering process window is the core of achieving high-quality THT solder joints. A professional Turnkey PCBA supplier, such as HILPCB, must master complex soldering processes. For THT components, automated wave soldering or selective soldering is primarily used:

• Wave Soldering: Suitable for boards with many THT components, offering high efficiency but significant thermal shock, requiring protection for nearby SMT components.
• Selective Soldering: Uses a miniature solder nozzle to precisely solder individual or a few THT joints. It allows customized soldering parameters (preheat time, soldering temperature, contact time) for each joint, perfectly addressing thermal management challenges in heavy copper PCBs or high-density mixed-technology boards while minimizing thermal impact on surrounding components.

Throughout the NPI EVT/DVT/PVT process, we repeatedly validate these processes through DOE (Design of Experiments) to lock in optimal production parameters and solidify them into the production workflow, ensuring consistent high quality for every board in mass production.

EMI and Thermal Management Co-Design for High-Current Connections

At the system level, THT connection design extends far beyond mechanical and electrical considerations.

Electromagnetic Interference (EMI) Suppression: High-current paths are primary sources of EMI. The di/dt generated by high-frequency switching creates significant induced voltage on current loops, resulting in conducted and radiated noise. THT connection pins and pads inherently introduce parasitic inductance and capacitance. Design optimization must minimize the physical length of power current loops through layout improvements and utilize multilayer board ground planes to reduce loop area. The robust structure of THT components makes them ideal as anchoring points for "island" grounding or shielding enclosures. By soldering multiple shield pins to the PCB's ground layer, a low-impedance path to ground is created for high-frequency noise, effectively suppressing EMI leakage.

Thermal Management Synergy: THT solder joints themselves serve as efficient heat dissipation channels. Large metal pins and plated through-holes can rapidly conduct heat from power devices (e.g., MOSFETs, IGBTs) to high-thermal-conductivity layers (High Thermal PCB) or directly to heatsinks mounted on the PCB's backside. This "board-level cooling" design is closely tied to the final Potting/encapsulation process. While potting materials (e.g., epoxy or silicone) provide excellent insulation, moisture resistance, and vibration protection, their thermal conductivity is typically far lower than copper. This means potting alters the original heat dissipation path, trapping heat internally. Thus, co-simulation during the design phase is essential, treating THT component cooling, PCB copper layer thermal conduction, and potting material thermal conductivity as an integrated system to ensure core device junction temperatures remain within safe limits under worst-case conditions.

For modern inverters integrating complex digital control logic, this co-design becomes even more challenging. The control core typically consists of high-density BGA (Ball Grid Array) chips. While ensuring THT soldering quality for power devices, Low-void BGA reflow quality for control chips must also be guaranteed. Voids in BGA solder joints compromise thermal performance and long-term reliability. These two aspects are mutually constraining in manufacturing: the substantial thermal mass of THT components affects BGA reflow temperature profile uniformity. This represents the ultimate test of a Turnkey PCBA provider's technical capabilities, requiring precise process control and deep expertise in mixed-technology manufacturing.

Maintenance & Replacement: The Difficult Trade-off Between Connection Reliability and Field Serviceability

The ruggedness of THT/through-hole soldering connections means they rarely require maintenance throughout a product's design life. This is critical for inverters installed in remote locations (e.g., photovoltaic plants in deserts or offshore wind farms), as any field service entails high labor, transportation, and downtime costs. However, this extreme reliability also brings the challenge of difficult repairs. Replacing a multi-pin THT power component is far more complex than replacing an SMT component. It requires professional rework equipment (such as a combined workstation with a hot air gun and solder sucker) and experienced technicians. Otherwise, during the disassembly process, the PCB's multilayer structure or solder pads can easily be damaged due to overheating, leading to the scrapping of the entire expensive PCBA.

Therefore, during the NPI EVT/DVT/PVT phases, the design team must carefully balance reliability and serviceability. A typical lesson from failure is: an early inverter design directly soldered all power devices to the mainboard and encapsulated the entire unit. When an IGBT module failed due to surge impact, the entire inverter had to be replaced as a whole, causing the customer's total cost of ownership (TCO) to skyrocket. In subsequent designs, the team learned from this lesson and redesigned vulnerable or future-upgradeable modules to connect to the mainboard via high-reliability THT connectors, while the core, less-prone-to-failure power paths continued to use direct soldering to ensure ultimate reliability. Potting/encapsulation was also modularized, further reducing repair complexity and costs. These decisions profoundly impact the product's market competitiveness and customer satisfaction.

Inspection and Traceability: From Process Control to Full Lifecycle Data Management

Ensuring the quality of every THT solder joint in tens of thousands of inverters requires strict inspection and process control. Beyond traditional manual visual inspection (AVI), modern production lines rely on more advanced methods:

• Automated Optical Inspection (AOI): Quickly examines solder joint appearance, such as solder wetting angle, glossiness, and the presence of solder balls, shorts, or cold joints.
• X-Ray Inspection: This is the "gold standard" for evaluating the internal quality of THT solder joints. It can penetrate components and PCBs to clearly observe the barrel fill of solder within the holes, ensuring compliance with the IPC-A-610 Class 3 standard requirement of over 75% vertical fill. It also detects internal voids, which are potential killers of long-term reliability.

In the era of smart manufacturing, all these inspection data should be deeply integrated with Traceability/MES (Manufacturing Execution System). Imagine this scenario: a faulty PCBA from the field is returned for analysis. By scanning the QR code on the board, engineers can instantly retrieve its complete "birth certificate" from the Traceability/MES system: which production line and time frame it was manufactured in; the selective soldering equipment ID used for its critical THT terminals, real-time temperature profile data at the time, batch numbers of the solder and flux used; and the original images and judgment results from AOI and X-Ray inspections. This end-to-end data management not only reduces root cause analysis time from weeks to hours when issues arise but also enables continuous optimization of process parameters through statistical analysis (SPC) of massive production data, allowing for prediction and prevention before defects occur. This is an indispensable core capability for delivering high-quality Through-Hole Assembly services and comprehensive Turnkey PCBA solutions. Similarly, the Low-void BGA reflow process for complex components like BGAs requires the same granular level of strict traceability management.

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Conclusion

In summary, THT/through-hole soldering is far from an outdated technology. In fields like renewable energy inverters, where demands for power, efficiency, and reliability reach their peak, it remains the most robust and reliable choice to meet the challenges of high voltage, high current, and harsh environments. From early-stage simulation and validation during NPI EVT/DVT/PVT phases, to system-level co-design with Potting/encapsulation, and throughout the production process with Traceability/MES monitoring, every application of THT technology highlights its irreplaceable core value.

Choosing a partner like HILPCB, which deeply understands the complexities of power electronics manufacturing, means you receive not just PCBA that meets specifications but also comprehensive assurance spanning design for manufacturability (DFM), process development, supply chain management, and rigorous testing. Our professional Turnkey PCBA service expertly handles complex hybrid processes, including THT/through-hole soldering and Low-void BGA reflow, ensuring your inverter products operate stably, efficiently, and safely over decades-long lifecycles, providing a solid and reliable hardware foundation for the future of green energy.

Related links

• Heavy Copper PCB
• high-thermal-conductivity layers (High Thermal PCB)
• Through-Hole Assembly services