PCB Tech - Advantages and disadvantages of PCBA packaging

Advantages and disadvantages of PCBA packaging
BTC (Bottom Terminal Component) can be translated as a bottom solder terminal device. It is a relatively new type of package. Its characteristic is that the outer connection terminal and the metal inside the package are integrated. There are many specific package names, including SON, DFN, QFN, LGA, etc. But it is actually divided into two categories, namely the peripheral square pad layout and the area array circular pad layout.

At present, imaging module devices (CIS), aviation, aerospace, navigation, motor cars, automobiles, outdoor LED lighting, solar energy and military enterprises, as well as various electronic products on smart terminals with high reliability requirements, the BTC application on the circuit board is very A wide range of special devices, such as solder ball array devices (BGA/CSPALP/POP) and QFN/LLP, are all facing the trend of miniaturization. For some smart phones, up to eight BTCs are used for each. BTC is also used in voltage regulators and power regulators, as well as many other automotive and industrial applications. Designers have found that using BTC in small packages and small PCBs has great benefits.

We are all very familiar with ball grid array packaging (BGA). From the physical structure, BTC and BGA are slightly different, which makes BTC and BGA different in all aspects such as cost, design, assembly and rework. BTC is like BGA without solder balls. It has excellent electrical performance and thermal characteristics, and is a very durable package, so there is no need to worry about damaging the pins during processing. The most attractive thing about BC is its price. This is why it can be widely used in high-volume products such as mobile phones and other mobile products.

Because BTC has no leads, it has many advantages, such as smaller package size and excellent electrical (ie resistance, capacitance, inductance) performance. In addition, because the heat generated by the BTC package is directly conducted to the thermal path of the PCB (the heat is from the silicon die to the silicon die to the copper pad and then to the PCB), they also have excellent thermal performance. The most important thing is that the BTC package is compatible with the standard SMT process (the same as the thermal path in the fine pitch QFP, there is no special intermediate link).

Of course, any type of packaging has its shortcomings, and BTC is no exception. The most significant problem is that the BTC terminal does not have good weldability. The solder end of the BTC is a surface, and the solder joint formed with the PCB processing pad is a "surface-to-surface" connection. The processability of BTC-type packages is relatively poor. In other words, it is difficult to weld. Frequent problems are voids in the weld, virtual welding or bridging of the surrounding solder joints. There are two main reasons for these problems. One is that the gap between the package body and the PCB processing is too small, the solder paste is easy to squeeze during patching, and the solvent volatilization channel in the flux is not smooth during soldering; the second is the heat sink pad and IO. The pad area is very different. When the solder paste deposition rate on the O pad is low, the phenomenon of component lifting and false soldering is easy to occur.

Another major issue of BTC is the flatness and coplanarity of the package. These packaging requirements are extremely high. The package and PCBmust be completely flat, and the amount of solder must be just right. If these conditions are not met, either an open circuit will occur due to insufficient explosive paste, or a large number of solder voids and bridges will appear on the side due to too much solder paste. .

In addition, since the package terminal does not protrude to the outside of the package, it is difficult to visually inspect and verify the solder interface. Given that this kind of package puts many higher requirements on assembly, inspection and rework, this means that this low-cost package may not immediately reduce the overall cost of assembly.