The JT-450: Soldering What SMT Cannot Reach
Every PCBA line has two soldering technologies working side by side: reflow for SMT (surface mount) and wave soldering for through-hole. While the SMT line processes boards with components sitting on the surface, the wave soldering machine handles the components whose leads pass through the board and emerge on the other side — connectors, large capacitors, transformers, relays, and power devices.
The JT-450 is our primary wave soldering system, with JT-350 units supporting lower-volume lines. Both are designed for lead-free operation with SAC305 alloy, the same solder chemistry used throughout our facility. They represent the "other half" of PCBA manufacturing — the half that SMT cannot address.
Why Through-Hole Still Matters
In an era of ever-shrinking SMD components, through-hole technology persists for good reasons:
Mechanical Strength. A through-hole connector soldered into a plated through-hole is mechanically far stronger than a surface-mount connector relying only on pad adhesion. For connectors that will be repeatedly mated and unmated — USB, HDMI, power jacks, terminal blocks — through-hole is the reliable choice.
Power Handling. High-current components (power transistors, heavy-gauge terminals, large inductors) generate heat during operation. Through-hole joints provide better thermal paths and higher current-carrying capacity than SMT joints of equivalent footprint.
Component Availability. Some specialized components — particularly transformers, large electrolytic capacitors, and power semiconductors — are simply not available in SMT packages. The design requires some through-hole content.
Mixed-Technology Boards. Most real-world PCBs are neither purely SMT nor purely through-hole. They are mixed-technology: SMT components on one or both sides, through-hole components on the top side, all soldered in a sequence of reflow then wave soldering.
How Wave Soldering Works
Wave soldering is fundamentally different from reflow. In reflow, solder paste is deposited on individual pads, components are placed, and the entire assembly is heated until the paste melts and forms joints. In wave soldering, the board passes over a flowing "wave" of molten solder that contacts all exposed metal surfaces simultaneously.
The JT-450 process:
Lead-free preheat temperatures are higher than tin-lead: typically 110-130°C topside, vs. 90-110°C for SnPb. The JT-450's preheat zones are calibrated for SAC305.
Dual Wave: Why Two Waves?
Single-wave systems still exist, but dual-wave is the modern standard — and for good reason. The two waves serve different purposes:
| Wave | Purpose | Characteristics |
|---|---|---|
| First (Turbulent) | Penetration and wetting | High pressure, turbulent flow, forces solder into tight spaces |
| Second (Laminar) | De-bridging and finishing | Smooth flow, controlled exit angle, removes shorts and excess |
Without the first wave, solder may fail to penetrate dense connector pin fields. Without the second wave, the board exits with bridges between closely spaced pins. The combination is essential for modern mixed-technology boards.
Lead-Free Challenges in Wave Soldering
Wave soldering with SAC305 is significantly more demanding than with traditional Sn63/Pb37:
Higher temperature. Solder pot temperature runs at 260-270°C vs. 240-250°C for SnPb. This increases oxidation rate (dross formation) and thermal stress on the PCB.
Dross formation. SAC305 oxidizes rapidly at wave temperatures, forming dross (oxidized solder waste) at 2-3× the rate of SnPb. The JT-450's solder pot design and nitrogen blanketing (where equipped) minimize dross, but it remains an operational cost.
Copper dissolution. Lead-free solder dissolves copper from the PCB pads and through-hole barrels more aggressively. Wave contact time must be carefully controlled — typically 2-4 seconds — to prevent copper erosion while ensuring adequate wetting.
Wetting performance. SAC305 does not flow as readily as SnPb. Board surface finish matters more: ENIG (Electroless Nickel Immersion Gold) and HASL (Hot Air Solder Leveling) give better results than OSP (Organic Solderability Preservative) in wave soldering.
The JT-450 manages these challenges through precision thermal control, adjustable conveyor speed, and programmable wave height — all parameters tuned per product.
JT-450 vs. JT-350
The JT-450 and JT-350 are from the same product family, with the JT-450 being the larger, higher-capacity system:
| Parameter | JT-450 | JT-350 |
|---|---|---|
| Max PCB Width | ~450mm | ~350mm |
| Preheat Zones | 3-4 zones | 2-3 zones |
| Solder Pot Capacity | ~500kg | ~350kg |
| Throughput | Higher | Standard |
For most production, the JT-450 handles the large-format and high-volume boards, while JT-350 units serve smaller or lower-volume products.
Why Wave Soldering Quality Matters
Through-hole joints are often the most mechanically stressed connection points on a PCB — connectors being pulled, power terminals carrying high current, large components subject to vibration. A poorly formed wave solder joint may pass initial electrical test but fail prematurely in the field.
The JT-450's dual-wave design, precision thermal control, and lead-free optimization ensure that every through-hole joint on every board meets IPC Class 2 or Class 3 acceptance criteria: smooth fillets, complete hole fill (minimum 75% for Class 2, 100% for Class 3), and no bridging or icicles.
For customers whose products will operate in harsh environments — automotive engine compartments, industrial machinery, outdoor equipment — this joint quality is not optional. It is the difference between a product that lasts and one that returns under warranty.
