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In the process of industrial projects, considering the controllability of PCB development schedule and risk, it is the first choice for most engineers to use mature core boards to promote the development and implementation of the project. So how to choose the connection between the core board and the bottom board, that is, the packaging of the core board? What are the advantages and disadvantages of various packages? And what are the precautions in the use process after the selection? Let's talk about these issues today.
Core board is an electronic motherboard that packages and encapsulates the core functions of MINI PC. Most core boards integrate CPU, storage devices and pins, which are connected to the supporting backplane. Because the core board integrates the general functions of the core, it has a core board which can customize the versatility of various backboards, which greatly improves the efficiency of the development of single-chip computers. Because the core board is separated as an independent module, it also reduces the difficulty of development and increases the stability and maintainability of the system. Especially in urgent and important projects, there are uncertainties in the development time and risk of high-speed hardware and underlying drivers from IC level R&D, and using core board as the main control is the first choice.
Of course, due to the large number of core board parameters and the limited space of this article, we will only talk about the core board packaging this time. The encapsulation of core board is related to the convenience of future production, the yield of finished products, the stability of field trial, the life of field trial, the convenience of troubleshooting and locating of faulty products, etc. Next, we discuss two common core board packaging forms.
I. Pass Packaging of Stamps
Stamp pass packaging is favored by electronic engineers for its IC-like appearance, welding and fixing methods. So many core boards in the market use this kind of package. Examples of stamp hole encapsulation styles are shown in Fig. 1:
What are the two types of core board packaging commonly used in industry? How to choose?
As can be seen from the picture above, the core plate of the stamp hole encapsulation style is as thin as a stamp, and the edge welding pin is very similar to the edge of a stamp, hence the name. This type of package is very strong because the connection between the bottom plate and the bottom plate is fixed by welding. It is also suitable for use in high humidity and high vibration.
For example, the island project, the coal mine project and the food processing plant project have the characteristics of high temperature, high humidity and high corrosion. Stamp holes are especially suitable for these kinds of project occasions because of the stable way of joint welding.
Of course, stamp hole packaging also has some inherent limitations or shortcomings, such as: low yield of welding products, unsuitable for multiple furnace welding, inconvenience in maintenance, disassembly and replacement, etc. The author has encountered many problems: high welding defect rate of patch machine caused by warping of core plate of stamp hole, loosening of main CPU caused by welding factory pasting core plate to back for secondary furnace welding, and discarding of bottom plate welding pad caused by maintenance and disassembly, etc.
Therefore, if you really have to choose stamp hole packaging because of the requirements of the use occasion, the problems that need to be paid attention to are: using manual welding to ensure the welding product rate, using machine welding to avoid sticking the core board for the last time, and preparing for high scrap rate. Especially the last point should be explained in particular, because most of the stamp hole core boards are chosen to obtain the polar repairing rate after the product arrives at the scene, so it is necessary to accept the inconvenience of production and maintenance of stamp hole encapsulation, and must accept the characteristics of high scrap rate and overall cost.
2. Packaging of Precision Plate-to-Plate Connectors
If we can't accept the inconvenience of production and maintenance brought by stamp hole packaging, perhaps the precision board-to-board connector packaging is a better choice. The encapsulation is in the form of base-to-base insertion. The core plate does not need to be welded in the production process. It is easy to insert and replace in the maintenance process. The core plate can be replaced by troubleshooting. So the package is also adopted by many products. The package style is as follows:
What are the two types of core board packaging commonly used in industry? How to choose?
As can be seen from the figure above, this kind of package can be plugged in and plugged out to facilitate production and maintenance and replacement. Moreover, because of the high pin density, more pins can be drawn in a small size, so the core board of this type of packaging is compact. It can be easily embedded into products with limited product size, such as roadside video stakes, hand-held meter readers, etc.
Of course, because of the high pin density, it is slightly more difficult to weld the base plate, especially in the sample stage of the product. When the engineer welds by hand, many engineer friends have been crazy in the manual welding process of this kind of package. Some friends melt the base plastic during welding, some lead to collective adhesion due to high pin density during welding, and some seem to be perfectly welded but the measured pin is short-circuited.
It is difficult to weld the base of the package, so even in the sample stage, it is better to ask professional welders to weld, or patch machine to weld. If unconditional machine welding is true, a manual welding procedure with high welding success rate is also provided here.
1. Spread solder uniformly on the pad (pay attention not too much, too much solder will raise the base pad, nor too little, too little will lead to virtual soldering);
2. Align the base to the pad (pay attention to the base with fixed column when purchasing the base, convenient alignment);
3. Use soldering iron to press each pin one by one.