What is a Wave Soldering Fixture?

A wave soldering fixture, also known as a wave soldering pallet, carrier, or jig, is a specialized tool used in the wave soldering process. Its primary function is to hold the printed circuit board (PCB) and protect components and areas on the board that are sensitive to high temperatures or do not require soldering, allowing them to pass safely and precisely through the molten solder wave to complete the soldering process.

Simply put, it's like putting a "protective suit" on the PCB, exposing only the pins that need to be soldered.

  1. Main Functions of a Wave Soldering Fixture 

      Selective Soldering:   Walls and covers on the fixture can precisely shield areas that do not require soldering, such as gold fingers, connectors, surface-mount components (already reflow soldered), and IC socket holes, preventing solder from entering and causing short circuits or contamination.

      Protecting Sensitive Components:   Some components (e.g., LEDs, electrolytic capacitors, plastic connectors) cannot withstand the high temperatures of wave soldering (typically 250°C - 265°C). The fixture can completely encapsulate and isolate them, providing thermal insulation and protection.

      Support and Prevention of Deformation:   Thin or large-sized PCBs are prone to bending and warping when heated. The fixture provides uniform support, effectively preventing board warping and ensuring soldering quality.

      Improving Production Efficiency:   The fixture can hold multiple small PCBs or irregularly shaped boards, enabling soldering of multiple boards in a single pass through the furnace, greatly improving production efficiency.

      Auxiliary Processes:   Some fixtures are also designed with turbulence columns or solder thieves to improve local soldering results and prevent bridging and icicles.

  2. Common Materials and Structures of Wave Soldering Fixtures 

  Materials: 

      Laminates:   The most commonly used is synthetic stone. It offers excellent high-temperature stability (long-term temperature resistance >280°C), extremely low thermal conductivity (excellent insulation), anti-static properties, and good mechanical strength, making it difficult to deform. It is the preferred material for high-end fixtures.

      Aluminum Alloy:   Good thermal conductivity and high strength, but poor insulation. It requires surface treatment (e.g., Teflon coating) to prevent solder adhesion. It is mostly used for support frames or in applications requiring extremely high strength.

      Bakelite:   Lower cost, but not as heat-resistant or durable as synthetic stone. It is prone to carbonization, deformation, and dust generation under long-term high temperatures, and has been gradually replaced by synthetic stone.

  Structure: 

      Base/Frame:   The main body of the fixture, used to support the entire PCB.

      Walls/Dams:   Raised edges on the fixture that block molten solder from flowing to areas that do not require soldering.

      Cover/Top Plate:   Used to press down and protect components on the top surface of the PCB.

      Clips/Pressure Bars:   Used to securely fix the PCB within the fixture to prevent displacement during furnace passage.

      Windows/Openings:   Areas where pins need soldering are precisely cut out to allow the solder wave to make contact.

      Locating Posts/Pins:   Ensure the PCB can be accurately placed in the designated position of the fixture.

      Turbulence Columns/Solder Thieves:   Small auxiliary structures, usually at the tail of the fixture, used to break surface tension and remove excess solder when the board exits the solder wave, preventing bridging.

  3. Design and Manufacturing Process 

      DFM Analysis:   Before designing the fixture, a Design for Manufacturability (DFM) analysis of the PCB layout, component types, temperature resistance, soldering requirements, etc., is required.

      3D Design:   Using professional CAD software, design the various components of the fixture based on the PCB's 3D model, accurately calculating window positions, wall heights, fixture tolerances, etc.

      CNC Machining:   Use CNC machines to perform precision milling, drilling, and cutting on synthetic stone plates or aluminum to produce the various parts of the fixture.

      Assembly and Inspection:   Assemble the processed parts and perform a trial fit with the actual PCB to check its fit, stability, and window accuracy.

  4. Usage Precautions 

      Cleaning:   Regularly clean the fixture of flux residues and oxides, as these can affect soldering quality and the fixture's insulation effect.

      Inspection:   Before each use, check the fixture for damage, cracks, or severe deformation, especially the clip and pressure bar mechanisms.

      Cooling:   The fixture temperature is very high after exiting the furnace and needs to be sufficiently cooled before reuse to extend its lifespan and prevent burns.

      Storage:   Store flat or vertically suspended to avoid deformation due to heavy pressure.

  5. Fixture Costs and Considerations 

Fixture costs range from several hundred to several thousand yuan, depending on their size, complexity, and materials. When deciding whether to use a fixture, the following need to be weighed:

      PCB Value and Complexity:   High-value or complex PCBs must use fixtures to ensure yield.

      Component Sensitivity:   Whether the board has a large number of heat-sensitive components.

      Production Volume:   For large-volume production, the fixture cost can be amortized, making it more economical.

  6. Summary: 

Wave soldering fixtures are indispensable process equipment in modern electronic assembly. Through precise mechanical design, they cleverly solve a series of problems such as selective soldering, component protection, and prevention of PCB deformation, and are key to ensuring high-quality and high-yield wave soldering production. Choosing a well-designed and high-quality fixture is a very important investment for electronic manufacturing enterprises.