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PCB Tech

PCB process SMT PoP CoC three automatic welding process flow and realization possibilities
2021-10-06
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Author:Aure

PCB process SMT PoP CoC three automatic welding process flow and realization possibilities




Comparison of three technological processes

Generally speaking, the SMT patching method we see more often is a carrot and a pit, that is, a land can only have one bungalow, but the technology of electronic component packaging is changing with each passing day, and the size is required to be smaller and smaller. Therefore, it is often seen that the parts are marked on the circuit carrier board and then used as normal SMD parts to be pasted on the final circuit board. For example, LGA packaging belongs to this type of technology. In addition, another part is sometimes marked on the part. What I have heard is that another BGA is added to the top of the BGA part. This packaging technology is commonly known as PoP (Package on Package), which is similar to building a building, and a piece of ground can be covered with more than two floors.


However, there is still a new SMT process called CoC (Chip on Chip). Since another BGA can be marked on the BGA, can Small Chips such as small capacitors or small resistances also be able to use SMT machines to achieve automatic welding processes? What is the purpose?

 


PCB process SMT PoP CoC three automatic welding process flow and realization possibilities

The PoP process for BGA usually comes from the needs of BGA parts vendors, so there will be many bumps on the top of the BGA package for another BGA for soldering, and the BGA itself will have solder balls. (solder ball), so the SMT machine does not need to do any special adjustments to put the BGA on the T/P (Top Package) of the PoP to the top of the BGA under the B/P (Bottom Package), and the soldering only needs to be adjusted and reflowed. Furnace temperature, its success rate is very high.

 

However, the general small resistor/capacitor/inductance (small chip) does not have enough solder to solder two small parts, so how to print the solder paste in the middle of the two parts has become a big problem, but the method is always People came up with it, and I really admire these engineers.


The purpose of CoC is to make L/C/R parts in parallel. Generally speaking, the chance of resistance and resistance welding in parallel is not great. If capacitors and capacitors are welded in parallel, the capacitance value can be increased. Some parts with large capacitors may be too expensive or fundamental If you can't buy them, you can consider parallel capacitors. There are functional requirements for zero external RC parallel or LC parallel.

 

CoC implementation method: purely consider the use of SMT for automated welding, without considering manual hand welding, SMT machines may need to be modified, you can ask SMT manufacturers to modify the program to achieve, B/C (Bottom Chip) is the next part, T/C (Top Chip) is the top part. At the beginning, solder paste is printed on the solder pads of B/C and T/C respectively, and both B/C and T/C are printed to their respective positions on the circuit board, and then It’s the point. Then use the suction nozzle of the SMT machine to pick up the T/C parts from the circuit board and stack them on top of the B/C. At this time, there should be some printed circuits on the T/C end points. The solder paste on the board is to use these solder pastes to solder the B/C and T/C parts together, so the key point is to adjust the pick-and-place procedure of the SMT machine, and the amount of solder paste originally printed on the T/C It may also need to be optimized and adjusted.