1. Process design

Surface mount device manufacturing, especially for fine pitch components, requires continuous monitoring of the process and systematic review. For example, in the United States, solder joint quality standards are based on IPC-A-620 and national solder standard ANSI / J-STD-001. Understanding these guidelines and specifications will enable designers to develop products that meet industry standard requirements.

2. Mass production design

The mass production design includes all mass production processes, assembly, testability, and reliability, and starts with the need for written documentation. A complete and clear assembly document is absolutely necessary for a series of transitions from design to manufacturing. Its related documents and CAD data list include bill of materials (BOM), list of qualified manufacturers, assembly details, special assembly guidelines, PC board manufacturing details and included Gerber data or IPC-D-350 program.

CAD data is of great help in developing testing and manufacturing tools, and writing programs for automated assembly equipment. It contains the X-Y coordinate position, test requirements, summary graphics, circuit diagrams and X-Y coordinates of test points

3. PC board quality

A sample is taken from each lot or a specific lot number to test its solderability. This PC board will first be compared with the quality specifications marked on the manufacturing PC. The next step is to reprint the solder paste on the solder pads. If an organic flux is used, it needs to be cleaned to remove residues. While evaluating the quality of the solder joints, we should also evaluate the appearance and size response of the PC board after reflow. The same inspection method can also be applied to the wave soldering process.

4. Development of assembly process

This step includes continuous monitoring of each mechanical action with the naked eye and automated vision devices. For example, it is recommended to use laser to scan the volume of solder paste printed on the surface of each PC board.

After placing the sample on the surface mount device (SMD) and reflowing it, the quality control and engineering staff need to check the soldering conditions on the pins of each component one by one. Each member needs to record the passive components and the number of pins Component alignment status. After the wave soldering process, it is also necessary to carefully examine the uniformity of the solder and determine the potential locations that may cause defects in the solder joints due to the close distance between the pins or the components.

5. Fine pitch technology

Fine pitch assembly is an advanced construction and manufacturing concept. The density and complexity of components are much larger than the current mainstream products in the market. If you want to enter the mass production stage, you must modify some parameters before entering the production line.

For example, the fine pitch component has a pitch of 0.025 or less, which can be applied to standard and ASIC components. The industry standards for these components have very wide tolerances. Because the tolerances of component suppliers are different from each other, the pad size must be tailored for this component or modified to truly improve the yield of assembly.

The pad dimensions and spacing generally follow IPC-SM-782A specifications. However, in order to meet the process requirements, the shape and size of some pads will be slightly different from this specification. For wave solder, the pad size is usually slightly larger in order to have more flux and solder. For some components that are usually kept near the upper and lower limits of the process tolerance, it is necessary to adjust the pad size appropriately.

6. Consistent orientation of surface mount devices

Although it is not absolutely necessary to design all components in the same orientation, for the same type of components, the consistency will help improve the efficiency of assembly and inspection. For a complex board, components with pins usually have the same orientation to save time. The reason is that the gripping heads for placing components are usually fixed in one direction, and the board must be rotated to change the placement orientation. As for the general surface mount devices, there is no problem in this respect because the gripper of the placement machine can rotate freely. However, if the wave soldering furnace is to be passed, the component must be aligned to reduce the time it is exposed to the flux.

The polarity of some polar components is determined as early as the entire circuit design. After understanding the circuit functions, the process engineer determines the order of placing components to improve assembly efficiency, but it has consistent directionality. Or similar components can increase their efficiency. If the placement orientation can be unified, not only can the speed of writing the placement component program be shortened, but also the occurrence of errors can be reduced.

7. Consistent (and sufficient) component distance

Fully automatic surface-mount device placement machines are generally quite accurate, but when designers try to increase the density of components, they often ignore the complexity of mass production. For example, when a high component is too close to a micro-pitch component, it not only obstructs the view of the pin solder joints but also hinders heavy tools or tools used during heavy work.

Wave solder is generally used in relatively low and short components such as diodes and transistors. Small components such as SOIC can also be used on wave solder, but it should be noted that some components cannot withstand the direct heat of the tin furnace.

In order to ensure consistent assembly quality, the distance between the components must be large enough to be exposed to the tin furnace uniformly. In order to ensure that the solder can contact each contact, the high component and the low and short component should be kept a certain distance to avoid the shielding effect. If the distance is not enough, it will also hinder the inspection and heavy work of components.

Industry has developed a standard set of applications for surface mount devices. If possible, use standards-compliant components whenever possible. This will allow designers to build a database of standard pad sizes and allow engineers to better understand process issues. Designers can find that similar standards have been established in some countries, and the appearance of components may be similar, but the pin angles of their components vary from country to country. For example, SOIC component suppliers from North America and Europe can meet EIZ standards, while Japanese products use EIAJ as their design guidelines. It should be noted that even if it complies with the EIAJ standard, the components produced by different companies will not be the same in appearance.

8. Designed to improve production efficiency

The assembly of a PCBA board can be quite simple or very complex, depending on the shape and density of the components. Complex design can make efficient production and reduce the difficulty, but if the designer does not pay attention to the details of the process, it will become very difficult. The assembly plan must be considered at the beginning of the design. Generally, as long as the position and orientation of the component are adjusted, its mass production can be increased. If a PC board has a small size, has an irregular shape, or has components close to the board edge, you can consider mass production in the form of a continuous board.

9. Test and repair

It is often inaccurate and time-consuming to use a small desktop test tool to detect missing components or processes. Test methods must be considered at design time. For example, if you want to use ICT test, you need to consider the design of some test points that the probe can touch on the line. The test system has a program written in advance, which can test the function of each component, can indicate which component is faulty or incorrectly placed, and can determine whether the solder joint is good. Detecting errors should also include short-circuits between the contacts of the components, and empty soldering between the pins and the pads.

If the test probe cannot reach every common junction on the line, it is impossible to measure each component individually. Especially for the assembly of fine pitches, it is necessary to rely on the probes of the automated test equipment to measure the points connected on all lines or the lines connected between the components. If this is not possible, then the next best thing is to pass the functional test. Otherwise, the customer will not use it until after the shipment.

ICT testing is to make different tools and test procedures without using products. If testing is considered during design, then the product can easily test the quality of each component and contact. However, the lack of tin and very small short circuits can only be checked by electrical testing.