3.4 Wave Solder Setup

Wave soldering is the original mass production technique, and its effectiveness is determined by the harmonious, disciplined alignment of four critical mechanical and thermal steps. This chapter details the non-negotiable setup parameters — from setting the conveyor angle for optimal drainage to balancing the turbulent chip wave with the smooth main wave — that ensures every single THT joint achieves a uniform, clean fillet without creating bridges or icicles.

3.4.1 What the Wave Must Achieve

Wave soldering is the original mass soldering process. Its reliability depends on sequential, repeatable process control. The wave's functional goal is simple: to achieve a complete, high-quality fillet on every THT joint with a clean, dripless exit.

Wave Process Flow

1. Preparation: Fingers and rails hold the PCB at a fixed conveyor angle and speed.
2. Fluxing and Preheat: Chemically clean the board and bring the top-side temperature into the required range.
3. Chip Wave (Turbulence): The first wave scrubs solder into tight pin-to-pin gaps and plated through-holes (PTHs).
4. Main Wave (Laminar): The second wave forms the final, smooth fillet and controls the peel-off.
5. Exit: Peel-off bars or air knives trim excess solder, preventing bridges and icicles.

3.4.2 Essential Hardware Components

Understanding the mechanical actors is key to tuning the process.

• Conveyor and Fingers: Titanium or stainless fingers transport the board (or pallet) at a fixed speed and angle. Cleanliness is paramount; dirty fingers lead to poor wetting and solder wicking along the board edge.
• Chip Wave (Turbulent): A high-energy wave that pushes solder upstream into challenging gaps. Necessary for achieving barrel fill and clearing small bridges in the middle of pin rows.
• Main/Lambda Wave (Laminar): A smooth, continuous flow that provides the final, controlled contact to finish the fillet and ensure a clean drainage upon exit.
• Pallets (Fixtures): Custom composite fixtures that expose only THT windows while shielding surrounding SMT components from solder splash.

3.4.3 Starter Settings and Profiling

Wave profile settings must be adjusted based on the alloy and the board's thermal mass.

Orientation: Boards must be positioned so long pin rows are perpendicular to the wave direction where possible. Parallel rows create channels that trap solder, inviting bridging.

3.4.4 Peel Control: The Quiet Exit

The primary function of the exit area is to cleanly separate the board from the molten solder, minimizing solder tails and icicles.

• Peel-Off Bar: A stationary bar (often titanium) set just downstream of the main wave. It creates a controlled point of contact to mechanically deflect and break the solder film. Set the height to lightly wipe the freshly formed fillet meniscus.
• Air/Nitrogen Knife: A narrow jet blowing along the direction of travel immediately after the main wave. This uses gas pressure to gently trim icicles. Use the smallest intervention that achieves a clean peel; excessive air flow creates ripples that can cause bridges.
• Timing: A small pause (dwell) after the main wave allows the fillet to stabilize before the air knife applies pressure.

3.4.5 Maintenance and Consistency

Wave soldering rewards routine maintenance. Process consistency depends on the physical health of the machine and the purity of the solder.

• Dross Management: Dross (oxidized solder) must be skimmed on a scheduled basis. Excessive dross interferes with pump stability and contaminates the working alloy.
• Solder Level: Keep the solder pot level precisely in spec. A low solder level fakes a short wave height, leading to non-fills.
• Flux System Cleanliness: Regularly clean spray heads or foam stones and log the flux density (e.g., specific gravity or °Bé) to ensure consistent chemical activity.
• Finger Health: Conveyor fingers must be regularly cleaned to prevent flux residue and solder build-up, which causes solder wicking along the PCB edge.

Final Checklist: Wave Solder Setup