Since the miniaturization and lightweight of electronic products have promoted the transformation of electronic components from plug-in components to SMD components, there are still some plug-in components that are restricted by various factors and cannot be converted into SMD components, so mixed circuit boards will always exist.
Regarding the welding of mixed circuit boards, whether it is wave soldering or manual welding, there is a problem of low efficiency, so it is particularly important to choose and use appropriate wave soldering fixtures.
Table of Contents
What is a wave soldering fixture?
Wave soldering fixture refers to a tool used to pass the soldering furnace during the wave soldering process. It is a jig used to carry the PCB board through the soldering furnace and complete the welding operation.
Typical application scenarios for using wave soldering fixtures:
1) Double-sided mixed assembly process, there are devices on the back and it is not a red glue process, so a jig is required.
2) When the component body exceeds the edge of the PCB board and cannot pass through the solder furnace, a jig is required.
3）The PCB board is a continuous board and is easily deformed when exposed to high temperatures, so a jig is required.
Role of wave soldering fixtures:
1) Prevent PCB deformation due to excessive temperature.
2) SMD components can be protected so that PCB can be safely passed through wave soldering.
3) It can provide good support for thin substrates or flexible PCBs.
Characteristics of wave soldering fixtures
1. The material has high strength and is easy to carry out precision machining.
2. It has high temperature resistance, good dimensional stability and is not easy to deform.
3. It has thermal conductivity, and the heat can be quickly and evenly transferred to the circuit board when passing through the oven.
4. Corrosion resistance, resistant to corrosion by flux and cleaning agents.
5. Comply with anti-static requirements.
6. When used in environmentally friendly products, environmental protection requirements must also be met.
7、Moisture-proof and good electrical insulation.
Common material for wave soldering fixtures
Fiberglass board
It is composed of glass fiber materials and high heat-resistant composite materials. It has high mechanical properties and dielectric properties, good heat resistance and moisture resistance. The advantage is that it is cheap, but the disadvantage is that it has a short service life.
Composition stone
An environmentally friendly stone, which is made of more than 95% natural stone powder, plus a small amount of polyester and adhesive, mixed, pressurized, and vibrated under vacuum. The disadvantage is that it is more expensive, and the advantage is that it has a long service life.
Types of wave soldering fixtures
Universal wave soldering fixtures
It is the simplest to make. It only requires one or several aluminum frames and a few screws. There is no need to use composition stone or fiberglass board material to make holes. The advantage is that the aluminum frame bracket can slide and can adapt to various board sizes, any board can be used, but the disadvantage is that it cannot protect SMD chip devices.
Ordinary wave soldering fixtures
It is suitable for boards that have undergone wave soldering in large quantities. Use composition stone or fiberglass board material to open holes, so that the soldering feet area where the tin water comes into contact can be soldered. The area without openings protects the components that have been pasted to prevent them from falling.
Wave soldering fixture with cover
Its function is to fix and cover the plug-in components. Because some plug-in components are tall and light, easy to float, and the welding is not beautiful and reliable, so the cover plate is needed to fix the plug-in components through wave soldering.
Hand dip wave soldering fixture
It is generally used in some small companies. Because wave soldering equipment is large in size and high in cost, most small companies do not have matching wave soldering equipment. When using a soldering oven to solder plug-in components, a hand-dip wave soldering jig is required.
PCB design factors affecting wave soldering
When designing PCB, the solderability of plug-in components needs to be considered. When designing PCB layouts, single-sided layouts and single-sided soldering components are generally given priority. When the PCB layout cannot satisfy single-sided soldering, a double-sided mixed layout will be used. In this case, The wave soldering assembly process and the entire cost of the assembly process need to be considered.
Pin distance between chip components and plug-in components
Since the fixture opening for wave soldering needs to be larger than the plug-in component pad, if the fixture opening is relatively small, it may lead to soldering leakage. If the opening is larger, it may cause the patch components that are closer to the plug-in pad to be separated from the plug-in pad. Therefore, when designing the layout, the distance between the chip component and the plug-in pad must be considered, which generally needs to be greater than 3mm.
Height limit for chip components near plug-in pins
When making the jig, it is necessary to wrap the patch material near the pins of the plug-in material. If the chip components near the pins of the plug-in material are too high, the protrusion of the jig at the corresponding position will be too high, which will affect the process of passing the oven. The contact between the solder and the plug-in pin pad may lead to the possibility of virtual soldering, so generally do not place chip components larger than 3.5mm near the plug-in pin.
Reserve craft edge
For PCBAs that need to be wave-soldered, a process edge must be left during PCB design, usually 3-5mm. This is to allow the fixture to support the width of the PCB contact and also to prevent the rails from damaging the components on the PCBA board when passing through the oven.
Design of soldering pad
For multi-pin plug-in components, such as pin headers, network transformers and other devices, when the pin spacing is less than 2mm, it is necessary to leave a tin pad on the edge of the pad to prevent the pins from being connected to the tin during wave soldering. Generally, the tin pad connected to the pin pad is teardrop-shaped, and the tin pad separated from the pad is generally rectangular.
Additional white oil solder mask
If the pin spacing is less than 1mm, you need to add white oil solder resist between the pins to prevent the pins from being connected to tin.
Wave soldering fixture refers to a tool used to pass the soldering furnace during the wave soldering process. It is a jig used to carry the PCB board through the soldering furnace and complete the welding operation.
- Universal wave soldering fixtures
- Ordinary wave soldering fixtures
- Wave soldering fixture with cover
- Hand dip wave soldering fixture
- Pin distance between chip components and plug-in components
- Height limit for chip components near plug-in pins
- Reserve craft edge
- Design of soldering pad
- Additional white oil solder mask
