Five types of PCB soldering process

Five types of PCB soldering process

Generally, we will encounter the following problems when doing PCB layout design and PCB soldering process. How many layers of boards should be used for this PCB? It supposes to be single-layer board, double board or multilayer board? How to protect ESD/EMI? 

Will the PCB soldering process assembly be single-sided or double-sided? Should electronic components use full through-hole plug-ins? Or full SMD patch? Or patch plus plug-in hybrid? This paper focuses on the PCB soldering process.

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    How many layers of PCB boards are used

    In PCB soldering process, the number of layers refers to the number of circuit layers of the PCB. The more layers, it means that the same surface area can carry more circuits, and then use vias as connections between layers.

    The more layers of PCB usually means that more functions can be designed with smaller PCB size, but the production cost is relatively more expensive. Generally speaking, the more advanced boards has more PCB layers. And at least one layer will be used as ground, and one layer will be used as power supply voltage.

    Single-sided or double-sided

    In PCB soldering process, this is related to the production cost of assembling the PCB. If possible, try to put all the parts on the same side of the board, which will greatly reduce the production process. Because even there is only one part on the other side, and a SMT production line is usually required for welding. If this part can be combined and moved to the same side as other parts, the cost of a production line can be saved.

    All in-line or full patch

    In PCB soldering process, it is best if you can do full through-hole in-line wave soldering process or full patch SMT process, so that you don’t need to open an additional production line. SMT and wave soldering belong to different welding processes.

    In fact, the current PCB Assembly factories are using less and less wave soldering furnaces. Try your best to reduce wave soldering process, because the electricity cost of opening a wave soldering furnace is very expensive.Even just to heat the entire tin furnace pool to the melting temperature.

    Does the SMT factory provide the red glue wave soldering process

    Not every EMS factory has the red glue manufacturing process. It is recommended to ask clearly before designing, so as not to fail to produce after the design is completed.

    Secondly, the wave soldering and reflow processes have different requirements for the pad distance and size design of the same electronic component. It is recommended to consult the SMT factory first to obtain the relevant DFM requirements.

    How does the EMS or SMT foundry calculate the PCBA foundry cost

    How does the EMS or SMT foundry calculate the PCBA  foundry cost

    Generally speaking, EMS (electronics manufacturing service) or SMT foundries mostly calculate the cost of the foundry based on labor hours, and a few calculate the cost of the foundry based on a certain percentage of the material cost in the BOM table, and all the necessary governance The tool fee will also be calculated on your behalf.

    If the assembly board will use both SMT and wave soldering processes, generally speaking, the unit working hours of SMT will be more expensive than wave soldering in PCB soldering process. Because SMT equipment is more expensive, and the quality requirements of operators are relatively high, so the relative salary will also be higher.

    In principle, if you can reduce the manufacturing process, you can save production costs, because no matter whether a production line only uses 1/10 or 1/2 of it, the basic cost of the entire production line will be fixed there after the line is opened. Costs will be reduced for less use.

    5 main PCB soldering process solutions

    Single panel full straight plug in wave soldering process

    The first kind of PCB soldering process is generally used for single-sided boards, all electronic parts are insert parts or through hole parts including resistors, capacitors, and inductors. Manual plug-ins insert parts into a single-sided board and then flow through wave soldering to solder the parts to the circuit board. This kind of board The biggest feature is that all the parts are on the same side of the circuit board, so the parts can be welded after only one wave soldering.

    In the early days when there were no SMD parts, almost all circuit board assemblies used this type of process. The disadvantage is that it requires a large circuit board space, and with the evolution of technology, many parts have been converted to SMD without plug-in models, so now it is rare to see the manufacturing process of this type of board.

    Occasionally, you can still see some cheap power supplies/transformers or mouse boards still using this process, because the parts are cheap, or because they need to use parts that can withstand high current or voltage, if you choose SMD models, it will be more expensive, and most boards still use low-cost paper circuit boards. There are also some special boards that need to use parts that can withstand high current or voltage. Such parts may not be replaced by SMD parts.

    Single sided patch SMT plus plug in wave soldering process

    Single sided patch SMT plus plug in wave soldering process

    Generally,the second kind of PCB soldering process is used on a single-sided board. SMD patches and through-hole plug-ins are placed on the same side of the circuit board. In this PCB soldering process, the board must first be printed with solder paste on the SMT line, and the SMD parts are printed on the board, and the SMD parts are reflowed. Solder on the board, and then go to the plug-in station. Manual or automatic plug-in machines insert the plug-in into the board, and then solder the plug-in to the board through wave soldering.

    As the size of boards is getting smaller and smaller, and SMD components are becoming more and more popular and cheaper, most of the consumer circuit board assembly processes are now almost developing towards SMD+plug-in. That is to say, most of the electronic parts on the current assembled circuit board use SMD packaging, and a small number of parts that cannot be replaced by SMD, or use through-hole plug-ins based on price considerations.

    Therefore, this type of board is currently the most economical circuit board assembly process.

    Double sided patch SMT plus dot red glue plus plug-in wave soldering process

    The third kind of PCB soldering process is an earlier process of assembling double-sided soldering. Early electronic components are still in the stage of transition from through-hole plug-ins to SMD component packaging. There will be at least 10 traditional through-hole plug-ins or more on a circuit board, and At that time, small parts (small chips) such as resistors, capacitors, and inductors were still above the size of 0603, and some even used 1206.

    So there is red glue on the second side of the board to fix the SMD parts, and then the wave soldering process appears after the plug-in, because the first and second solutions can only be used to arrange the electronic parts on a single-sided board, if the second side of the board can be connected Parts can be placed on both sides, which can greatly increase the utilization rate of the board and reduce the size of the board.

    However, if the second side of the board is soldered with amount of solder paste and then used for wave soldering, because there are still many plug-ins on the board, The solidified solder paste on the second side will be melted when it flows through the wave soldering furnace, and the electronic parts on the second side will fall into the solder pool, so the red glue process has been developed, and the red glue is generally irreversible epoxy Resin material, which can stick to SMD parts and will not re-melt even when flowing through a wave soldering oven.

    Double sided patch SMT plus plug in selective wave soldering process

    Double sided patch SMT plus plug in selective wave soldering process

    With the evolution of the times, this fourth type of PCB soldering process double-sided SMT chip process can be regarded as the most common chip design at present, because most of the electronic components can already find the SMD package model, and only a few of them need to withstand external forces. Based on the consideration of function and reliability, plug-in IO connectors have to use through-hole plug-ins to ensure that their soldering will not be damaged by rude guests.

    This PCB soldering process has abandoned the “red glue” process. A few parts that still need to be soldered by the wave soldering process can be considered to use the wave soldering mask carrier/tray to cover the parts that have been soldered in SMT. Then only expose the part feet that need to be welded by wave soldering.

    In addition, you can also consider introducing the popular selective wave soldering furnace equipment in recent years, which uses small tin furnaces and nozzles, and uses computerized stroke automatic control to solder through-hole parts from the bottom.

    However, the PCB soldering process of the above two through-hole plug-ins has a requirement for a keep out area, and it is necessary to consult the DFM requirement during design.

    In addition to the above two wave soldering and wave soldering-like processes, because there are not many through-hole plug-ins, some people will use some cheaper processes:

    1. Hand welding: Personally, I really don’t recommend hand welding, because the quality is difficult to control. False welding and empty welding often occur at the grounding pins. Parts with thin pins are a test of technology and eyesight. High-skilled workers are required, and manual long-term welding is required. , is not good for the health of the soldering iron hand.

    2. Robot arm or automatic welding equipment: automatic welding can be very cheap or luxurious. This kind of equipment generally uses soldering iron and tin wire, but let the machine replace manual welding, and use a simple XYZ three-axis table or more. Achieved, but the precision and parameters need more time to debug.

    In fact, there is also a through-hole reflow soldering (PIH, Paste-in_Hole) process. Although it also has through-hole inserts, after improving the heat resistance level of the material, the through-hole inserts can be used as SMD parts for patching and passing through the reflow oven.

    Full double sided patch SMT

    Full double sided patch SMT

    At present, almost all smartphones and some consumer electronics products use the fifth The first kind of PCB soldering process. This is because today’s smartphones almost only have a Type-C or lighting IO connector, and at most an earphone can be added. In addition, smartphones are personal items. 

    Generally, customers will take good care of them and will not insert them roughly. Therefore, SMD connector models can be used. As long as there are some stoppers and anti-lifting mechanisms in the design, the warranty period can be guaranteed. Or there will be no connector drop problem during the lifetime.

    FAQ

    In PCB soldering process, the number of layers refers to the number of circuit layers of the PCB. The more layers, it means that the same surface area can carry more circuits, and then use vias as connections between layers. The more layers of PCB usually means that more functions can be designed with smaller PCB size, but the production cost is relatively more expensive. Generally speaking, the more advanced boards has more PCB layers. And at least one layer will be used as ground, and one layer will be used as power supply voltage.
    In PCB soldering process, this is related to the production cost of assembling the PCB. If possible, try to put all the parts on the same side of the board, which will greatly reduce the production process. Because even there is only one part on the other side, and a production line is usually required for welding. If this part can be combined and moved to the same side as other parts, the cost of a production line can be saved.
    Not every EMS factory has the red glue manufacturing process. It is recommended to ask clearly before designing, so as not to fail to produce after the design is completed. Secondly, the wave soldering and reflow processes have different requirements for the pad distance and size design of the same electronic component. It is recommended to consult the SMT factory first to obtain the relevant DFM requirements.

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