Our common computer boards are basically epoxy resin glass cloth-based double-sided printed circuit boards, one of which is a plug-in component and the other side is a component foot welding surface. It can be seen that the solder joints are very regular. We call it the pad for the discrete soldering surface of the component feet. Why are other copper wire patterns not tinned? Because in addition to the pads that need to be soldered, the surface of the rest has a solder mask that is resistant to wave soldering. Most of the surface solder masks are green, and a few are yellow, black, blue, etc., so the solder mask oil is often called green oil in the PCB industry. Its function is to prevent bridging during wave soldering, improve soldering quality and save solder. It is also a permanent protective layer of the printed board, which can prevent moisture, corrosion, mildew and mechanical scratches. From the outside, the green solder mask with smooth and bright surface is a green oil for film-to-board photosensitive heat curing. Not only does the appearance look good, but more importantly, the precision of the pads is high, thereby improving the reliability of the solder joints.
We can see from the computer board that there are three ways to install components. A plug-in installation process for transmission, inserting electronic components into the through holes of the printed circuit board. In this way, it is easy to see that the via holes of the double-sided printed circuit board are as follows: one is a simple component insertion hole; the other is a component insertion and double-sided interconnection via hole; The fourth is the substrate mounting and positioning holes. The other two installation methods are surface mounting and direct chip mounting. In fact, the direct chip mounting technology can be considered as a branch of surface mounting technology. It directly sticks the chip on the printed board, and then uses the wire bonding method or the tape carrier method, the flip chip method, the beam lead method and other packaging technologies to interconnect to the printed circuit board. board. The welding surface is on the component surface.
Surface mount technology has the following advantages:
1. Since the printed board eliminates a large number of large through holes or buried hole interconnection technology, the wiring density on the printed board is increased, and the area of the printed board is reduced (generally one-third of the plug-in installation), and at the same time It can reduce the design layers and cost of the printed board.
2. The weight is reduced, the seismic performance is improved, and the gel solder and new welding technology are adopted to improve the product quality and reliability.
3. Due to the increased wiring density and the shortened lead length, the parasitic capacitance and parasitic inductance are reduced, which is more conducive to improving the electrical parameters of the printed board.
4. It is easier to realize automation than plug-in installation, improve installation speed and labor productivity, and reduce assembly cost accordingly.
It can be seen from the above surface mounting technology that the improvement of circuit board technology is improved with the improvement of chip packaging technology and surface mounting technology. Now the surface mount rate of the computer boards we look at is constantly rising. In fact, this kind of circuit board cannot meet the technical requirements by using the screen printing circuit pattern of the transmission. Therefore, for ordinary high-precision circuit boards, the circuit patterns and solder mask patterns are basically made of photosensitive circuits and photosensitive green oil.
With the development trend of high-density circuit boards, the production requirements of circuit boards are getting higher and higher, and more and more new technologies are applied to the production of circuit boards, such as laser technology, photosensitive resin and so on. The above is only a superficial introduction to the surface. There are many things in the production of circuit boards that are not explained due to space limitations, such as blind buried vias, winding boards, Teflon boards, lithography technology, etc.
