PCB Technical - Discussion on SMT Technology of Printed Circuit Board

In the mass PCB production, we usually use fully automatic printing machines for printing (that is, coating solder paste). When the printed circuit board (PCB) enters the printing machine and is coated with solder paste, it must be fixed in the printing machine., There are usually two ways to fix the printed circuit board (PCB) of the printer: the first is to convey and position the guide rail; the second is to fix and position the bottom of the conveying guide by vacuum suction.

For a thin and fragile printed circuit board (PCB), if solder paste is applied in the first printing machine that fixes the printed circuit board (PCB) method, we will see the printed circuit board After the PCB is placed on the transfer rail of the printing machine and enters a proper position, the two transfer rails will clamp the printed circuit board (PCB) towards each other, which will cause the middle part of the printed circuit board (PCB) to slightly bulge. On the one hand, this clamping force is easy to cause the PCB to break; on the other hand, the printed circuit board (PCB) is raised in the middle, which makes the entire printed circuit board (PCB) to be coated uneven. This will affect the coating quality of the solder paste.

If the solder paste is applied to the printer of the second fixed printed circuit board (PCB) method, the above situation can be avoided, because in this fixed printed circuit board (PCB) method, the conveying rails are not facing each other Movement, then no opposing force will be applied to the two sides of the printed circuit board (PCB), and the middle of the PCB will not bulge. This kind of printer relies on the vacuum suction device under the conveying rail to hold the printed circuit board (PCB) Adsorbed on the conveying rail, the printed circuit board (PCB) will not be broken by the external force of the clamping. In addition, we will see that the bottom of the printed circuit board (PCB) is suspended in the middle. In order to ensure a thin PCB surface is flat and not bend when coating, we will add a self-made platform to the vacuum suction device to support the printed circuit board (PCB) during actual operation. The area of the platform can be compared with the printed circuit board (PCB). The printed circuit board (PCB) is matched, thus avoiding the problem of the uneven surface of the printed circuit board (PCB) that affects the coating quality.

In order to ensure the yield and product quality, the second type of printing with vacuum adsorption and fixing function is used for production.

After the solder paste is applied, it enters the patching process. Similarly, before the printed circuit board (PCB) enters the placement machine for placement, it must first be fixed in the placement machine. There are usually two ways for the placement machine to clamp and fix the printed circuit board (PCB). The first is to clamp the printed circuit board (PCB) by moving the transfer rails on the placement platform to move toward each other. Thereby, the printed circuit board (PCB) is fixed and positioned; the second type is that a compression strip is installed on the transmission rail. When the printed circuit board (PCB) advances to the corresponding position on the transmission rail, the compression strip on the rail is Automatically press down, press both sides of the printed circuit board (PCB) on the guide rail to fix and position. No matter which of the above-mentioned printed circuit board (PCB) fixing methods are used, there is no support at the bottom of the printed circuit board (PCB), which forms a suspension. If the printed circuit board (PCB) is thin and easy to break During placement, with the movement of the placement platform and the movement of the placement, it cannot be fully guaranteed that the printed circuit board (PCB) surface will not bend. This will affect the accuracy of the placement of the chip. In addition, the first printed circuit board (PCB) method is for the thin and fragile printed circuit board (PCB), which makes the printed circuit board (PCB) board The opposite clamping force on both sides can easily cause the middle of the printed circuit board (PCB) to bulge. If the printed circuit board (PCB) is a jigsaw, it may even cause the joint to break. For this reason, in actual operation, we will use the printed circuit board (PCB) to be fixed in a custom-made tray, and then the tray is sent to the conveyor rail, into the placement machine for placement, so that the printed circuit board (PCB) It will not be directly broken by the external force given by the guide rail, and the tray plays a supporting role for the printed circuit board (PCB). During placement, the impact of the printed circuit board (PCB) without support is prevented from being deformed. The problem of the accuracy of the placement of the patch. Using this method, we require good consistency between the trays (including the shape, frame, size and the size related to the positioning of the printed circuit board (PCB)). The consistency of the tray directly affects the accuracy of the placement position.

Of course, the above method is not perfect, it also has some flaws. Because this method requires relatively high pallet manufacturing, in addition to the high consistency requirements, there is another problem to be solved, that is, the fixed problem of the printed circuit board (PCB). Therefore, pay attention to the way of fixing the printed circuit board (PCB) when making the pallet. It is necessary to ensure that the printed circuit board (PCB) cannot be shaken in the pallet, but also to make the printed circuit board (PCB) easy to pick and place. It increases the difficulty and cost of making the pallet. In view of this, we propose another solution. This method is to make the pallet into a simple frame, and the printed circuit board (PCB) is fixed in the pallet by vacuum The method of adsorption makes it easier to make the tray, to ensure consistency, and to pick and place the printed circuit board (PCB). However, this method requires a slight modification to the existing placement machine. Because the current placement machine does not have the function of vacuum adsorption to fix the PCB, it is necessary to add a small vacuum adsorption device, and the opening of the vacuum pump of the device needs to be synchronized with the movement of the conveying rail to clamp and fix the printed circuit board (PCB).