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Six traps encountered in manual to mechanical PCBA assembly circuit boards
In the past, it was not difficult to find surface mount or through-hole chip. However, about ten years ago, manufacturers gradually stopped manufacturing through-hole technology wafers. In many cases, the latest products are only small QFN (quadrant flat no-lead package) or wafer-level BGA (ball grid array package).
There are many ways to use most of these chips. Under the agitation of the creativity of PCB factories, only a few components used in the industry are unusable.
1. Consider moisture
Although it doesn't make sense at first glance, plastic absorbs moisture, and it is not only when the whole piece of plastic is thrown into the water that it will be affected. As long as the plastic chip is exposed to the air, it will absorb moisture. If the moisture-absorbing chip is put into a reflow oven, the result will be like popcorn in a microwave oven.
When the moisture is heated, it will turn into water vapor. If it does not vent fast enough, the water vapor will hold the chip apart. Moreover, these cracks are invisible to the naked eye, making the product very unstable. Some DIY players often put the components outside after opening the kit, and don't particularly think about storing these components in a proper environment.
If you want to send the design for mechanical PCBA assembly, you can do two things for humidity-sensitive components. First, there is no need to order components in advance, order them when you need them, or keep the sealed packaging after the components arrive. Otherwise, you can also recycle damp components. If you tell the manufacturer that there is such a situation, ask them to bake those components before PCBA assembly, which can also solve the problem of dampness.
2. Don't save solder mask
If you order without soldermask or silkscreen, some circuit board manufacturers will offer discounts. This is no problem in manual PCBA assembly, because you can adjust the amount of solder used with the naked eye.
Solder mask can improve the quality of solder joints
However, if it is in the reflow furnace, when the solder is soldered to the circuit board through the template, some of the solder will reflow to the copper sheet, resulting in insufficient solder at the tip of the component and unable to secure the joints securely. Although the solder mask costs money, it can improve the stability of the contact, which is more cost-effective in the long run. Moreover, choosing different colors of solder mask can also make the board look more personal!
3. The screen is also very important
The screen has nothing to do with stability, but the screen will affect the accuracy of PCBA assembly. Ideally, the CAD file will tell the PCBA assembly machine the precise position, angle and direction of each component, but things are not perfect.
The size of the component may be wrong, and the label may be unclear. In many cases, the CAD file alone is not enough. The advantage of silk screen is to leave traces of data errors. If you don't want the PCB to be filled with polarity marks or object names, you can put these notes in the file layer of the production software, and then ask the PCBA assembly factory to read the instructions on that layer.
4. Don't be afraid of surface mount
One of the easiest ways to ensure that the board can be made by hand is to insert components with through holes. However, this will limit the design possibilities and cannot apply many new technologies. Of course, you can buy an additional circuit board-a small surface mount chip that is attached to the PCB with solderable connectors on the top. Many functions can be solved in this way, but this is not a panacea. Those products are very useful, but take up a lot of space, and the price will be more expensive than a board.
Through the machine PCBA assembly, the small board on the right can do what the two boards on the left can do together.
If you are doing product design and you don’t use many boards, you can consider additional circuit boards. However, if you want to produce a thousand boards, please redesign the PCB. Just don't forget the bypass capacitor or other components. In addition, many additional circuit boards are open source, so you can directly take a usable circuit to design!
5. Cannot use vias on solder pads
There are pins or solder pads under QFN and BGA, which are usually out of touch. For the reflow furnace, this is no problem, but what if you want to solder by hand? Many people add vias to the chip holder, fix the components on the board with tape, turn the board over, and pass the soldering iron and solder through the vias. In this way, it is indeed possible to manually solder most surface mount components without connectors.
After reading this, you probably have guessed what I am going to say, and this trick can also cause problems in mechanical PCBA assembly. The solder will flow down the via hole and run to the other side of the circuit board, which may cause a short circuit on the back side, fall off of the components on the front side, or inability to securely connect all the solder pads, etc. If you use the via hole manual soldering method, then Before the machine PCBA assembly, the PCB board must be redesigned and the vias must be removed.
6. Do it!
However, a few years ago, the tools and services for producing electronic products were still very complicated and expensive. For amateurs, it was almost impossible to put their own small topics into production and start a small business. Today, things have changed. It is not so difficult to do a hardware business. Almost anyone can give it a try.
