Due to advances in packaging technology, the electrical performance of SMD IC is better than THT IC.Integrated circuit packaging not only plays the role of the internal bonding point of integrated circuit chip and external electrical connection, but also provides a stable and reliable working environment for the integrated circuit chip, plays a role of mechanical and environmental protection for the integrated circuit chip, so that the integrated circuit chip can play a normal function.
People try to package the chip directly On the PCB. There are usually two methods of packaging: one is the COB (Chip On Board) , and the other is the reverse assembly welding method.The Bare Chip applicable to the COB method is also called the COB Chip, while the Bare Chip applicable to the reverse assembly welding method is called the Flip Chip, FC for short. The two have different structures.
(1) COB chip.The welding area and chip body are on the same plane, and the welding area is evenly distributed around the area. The minimum area of the welding area is 90um by 90um, and the minimum spacing is 100um.Since the welding area of COB chip is distributed around, the increase of I/O is limited to a certain extent. In particular, the welding area is connected to the PCB pad via wire welding. Therefore, PCB bonding pads should have the corresponding number of pads and be arranged in the surrounding area, so as to adapt to it.So the difficulty of PCB manufacturing process also increases.In addition, COB heat dissipation also has some difficulties.
(2) FC flip chip.The so-called flip Chip technology is also known as Controlled Collapse Chip Connection, C4) technology.It is the circuit chip with convex point electrode face down (flip), so that the convex point becomes the solder joint of chip electrode and substrate wiring layer, through welding to achieve a solid connection, this assembly method is also known as FC method.It has the advantages of simple craft, high installation density, small volume, good temperature characteristics and low cost.It is especially suitable for making hybrid integrated circuits.
The difference between FC and COB is that the solder joints are arranged on the chip in a plane array, and the solder area is made into a convex point structure. The outer layer of the convex point is Sn-Pb solder. Therefore, FC can be placed on the PCB in the welding process, and SMT method can be applied to realize welding.
The chip integration on the chip using FC flip chip technology is the application of multi-chip technology.
FC flip chip has the characteristics of small crosstalk, especially suitable for the bare chip multi-input/output, electrode whole surface arrangement, welding spot miniaturization trend of high-density development, is the most promising one of the bare chip welding technology.So FC flip chip technology has become the support technology for MCM of multi-chip components, and has been widely used in the chip welding of BGA, CSP and other new miniaturized components and components.