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PCB Tech

PCB Tech - The impact of PCBA imposition on SMT factory quotation

PCB Tech

PCB Tech - The impact of PCBA imposition on SMT factory quotation

The impact of PCBA imposition on SMT factory quotation

2021-10-30
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Author:Downs

Why the number of PCB circuit boards is important? Generally speaking, when PCB R&D and design engineers determine the appearance and shape of the printed circuit board, they should immediately proceed with the plywood/joint board/connected board work of the circuit board. The purpose of the puzzle is to increase the output of the production line and reduce the loss of the board.

The most common connecting board is to combine two or more pieces of the same circuit board into a large circuit board, such as 2 in 1 (two in one), 3 in 1 (three in one), 4 in 1 (four in one), etc. ; It is also used to combine different shapes of circuit boards into a large board, but it is rare, because it is difficult for the production tube to match the exact number of different boards when arranging the production; there are also cases where the same board is made into a double-sided board. The so-called double-sided board That is to say,

pcb board

the top and bottom sides of the configuration. This is usually used on circuit boards with fewer parts, such as mobile phone boards, because it can make full use of the long-term boarding function of SMT to increase efficiency, but the disadvantage is that it is used. It is limited and may cause uneven heating. For example, some circuit boards will concentrate heavier parts on one side, and then this side will be used as the second part to prevent the heavier parts from falling. Of course, this kind of board The double-sided design cannot be adopted; some boards may have heat-absorbing parts (such as large-area ATM card reader slots), which is not suitable for the double-sided design.

Basically, when designing several boards, the following factors should be considered. It should be noted that in the end, they should be converted into money as the final measurement standard. Considering the best utilization rate of circuit boards, ordinary circuit board manufacturers will have their basic standard board sizes in order to quickly mass produce and reduce costs, such as 16.16"x16.16", 18.32"x18.32", 20.32"x20. 32",... etc. What we have to do is to use up all these plates as much as possible, that is to say, choose a suitable standard plate size and stuff the plates in to achieve the highest utilization rate of the plates. Because the price of the circuit board will be priced according to the size of the board, the more circuit boards can be packed in a board, the cheaper the price of the circuit board. Of course, the price of the circuit board has to consider how many layers of the board, how many holes to drill, whether there is HID... etc.

Considering the production efficiency of the SMT chip processing section in PCBA processing, SMT processing lines usually have the so-called long-term and short-term points. The short-term line means the line is shorter. Most of them only have a fast machine and a slow machine. A fast machine; a long line means a longer line, and a few more fast machines and slow machines. But no matter the length of the line, there will always be a solder paste printing machine. Generally speaking, taking a plywood with a board length of 150mm as an example, it takes about 35-40 seconds to print the solder paste once. If only 2 in 1 plywood is used for input SMT is short-term, so the time allocated for each machine may be about 10 to 26 seconds. Obviously, the time is all lower than the time of solder paste printing, that is to say, the subsequent pasting machines are waiting for the solder paste printing machine, so This results in idle SMT machines and reduces production capacity. If the 2 in 1 connecting plate is changed to 4 in 1, then the efficiency will be improved immediately (the output per hour), the output per hour: {[60 (seconds/minute) x 60 (minutes/hour)] / Bottleneck time (seconds)} x number of plywood.

But general PCB manufacturers would prefer to have as few as possible the number of connected boards, because this can avoid the loss of cross board (X-board). The so-called cross board is a bad board with more than one board in the plywood. The general SMT manufacturing factory does not want to accept this kind of board because it will cause a loss of efficiency. However, this kind of circuit board cannot be absolutely avoided in the manufacturing process, so even the board The more the number, the more the number of scrapped circuit board factories will be, and the relative cost will increase. As mentioned at the beginning, the final result has to be converted into money to calculate the optimal number of plates to be used and connected. And the results may be different for different board factories and different SMT factories.