PCBA Tech - 8 principles and 15 precautions of PCBA processing

1. Preferred crimping and PCBA surface mount components

Surface mount parts and crimping parts, with good technology.

With the development of component packaging technology, most components can be purchased in packaging categories suitable for reflow soldering, including plug-in components that can be reflow soldered by through-holes. If the design can achieve complete surface installation, it will greatly improve installation efficiency and quality.

crimping components are mainly multi-pin connectors. This kind of packaging also has good manufacturability and connection reliability, which is also the preferred category.

2. Take the PCBAmounting surface as the object, and consider the packing ratio and pin spacing as a whole

Package size and pin pitch are the most important factors affecting the entire circuit board process. Under the premise of selecting surface mount components, a group of packages with similar or appropriate technical performance should be selected to paste a certain thickness of stencil printing onto a PCB with a specific size and mounting density. For example, for mobile phone boards, the selected packaging is suitable for printing with 0.1mm thick steel mesh solder paste.

3. Shorten the process path

The shorter the process route, the higher the production efficiency and the more reliable the quality. The optimal design of the process path is as follows:

Single-sided reflow soldering;

Double-sided reflow soldering;

Double-sided reflow soldering + wave soldering;

Double-sided reflow soldering + selective wave soldering;

Double-sided reflow soldering + manual soldering.

4. Optimize component design

The main component layout design is mainly related to the component layout direction and spacing layout. The arrangement of the components must meet the requirements of the welding process. Scientific and reasonable design can reduce the use of incorrect welding tools and joints, and optimize the design of the steel mesh.

5. Consider the design of welding pad, welding resistance and steel mesh window

The design of pad, solder resist and stencil window determines the actual distribution of solder paste and the process of solder joint formation. Coordinating the design of the welding pad, welding resistance and steel mesh is very important to improve the welding throughput speed.

6. Focus on new packaging

The so-called new package does not completely refer to the new package on the market, but refers to the fact that your own company has no experience in using these packages. For new package import, small batch verification must be performed. Other people can use it, but it does not mean that it can also be used. Under the premise of using it, you should understand the characteristics of the process and the scope of the problem, and master the countermeasures.

7. Focus on BGA, chip capacitors and crystal oscillators

BGA, chip capacitors and crystal oscillators are typical stress-sensitive components, and PCB bending and deformation should be avoided as much as possible during welding, assembly, workshop rotation, transportation, use and other links.

8. Study cases to improve design standards

Manufacturing design rules are derived from production practices. It is very important to improve the design of manufacturability to continuously optimize and improve the design rules according to the continuous occurrence of poor assembly or failure.

When engineers design PCBA boards, they must start from reducing costs and improving assembly quality on the premise of meeting the requirements of the overall mechanical and electrical performance, mechanical structure and reliability. So, what issues should be paid attention to in the design of PCBA board manufacturability? Share 15 attention issues for everyone.

1. Minimize the number of PCB layers. Can use single-sided board instead of double-sided board, and can use double-sided board instead of multi-layer board, so as to reduce PCB processing cost as much as possible.

2, try to use reflow soldering process, because reflow soldering has more advantages than wave soldering.

3. Minimize the process of PCB assembly process and try to use no-clean process.

4. Whether it meets the requirements of SMT process and equipment for PCB design.

5. Whether the PCB shape and size are correct, and whether the small size PCB considers the splicing process.

6. Whether the clamping edge design and positioning hole design are correct.

7. Whether the positioning holes and non-grounding mounting holes are marked as non-metallized.

8. Whether the Mark graphic and its position meet the requirements, and whether 1~1.5mm is left around to the solder mask.

9. Have you considered the requirements of environmental protection?

10. Whether the selection of substrate materials, components and packaging meet the requirements.

11. Whether the PCB pad structure (shape, size, spacing) meets the DFM specification.

12. Lead width, shape, spacing, and whether the connection between lead and pad meets the requirements.

13. Whether the overall layout of the components and the minimum spacing between components meet the requirements; whether the rework size is considered around the large components, and whether the polarity arrangement direction of the components is as consistent as possible.

14. Whether the aperture and pad design of the plug-in components meet the DFM specification; whether the distance between adjacent plug-in components is conducive to manual plug-in operation.

15. Whether the solder mask and screen patterns are correct, and whether the component polarity and IC pins are marked.