1.3ccga (ceramic cloud grid array ceramic column grid array)
CCGA, also known as SCC (solder column carrier), is another form of CBGA when the size of ceramic body is greater than 32mm×32mm (see Figure 5). Unlike CBGA, 90Pb/ 10Sn solder columns are connected to the lower surface of ceramic carrier instead of solder balls. The array of solder columns can be completely or partially distributed. The common solder column has a diameter of about 0.5 mm and a height of 2.20. CCGA has two forms, one is that the solder column is connected with the ceramic bottom through * * * crystal solder, and the other is that the fixed structure is cast. The solder column of CCGA can bear the stress caused by the mismatch of thermal expansion coefficient TCE between PCB and ceramic carrier. A large number of reliability tests have confirmed that CCGA with package size less than 44mm×44mm can meet the industrial standard thermal cycle test specification. The advantages and disadvantages of CCGA are very similar to those of CBGA. The only obvious difference is that the solder column of CCGA is more vulnerable to mechanical damage than the solder ball of CBGA in the assembly process. Some electronic products have begun to use CCGA packaging, but CCGA packaging with I/O number between 626 ~ 1225 has not been mass-produced, and CCGA packaging with I/O number greater than 2000 is still under development.
Fig. 5CCGA (ceramic column grid array)
1.4 tbga (ball grid array with ball grid array)
Fig. 6 internal structure of tbga
TBGA, also known as ATAB(Araay Tape Automated Bonding), is a relatively new BGA package type (see figure 6). The carrier of TBGA is copper/polyimide/copper bimetallic layer, and the copper wire used for signal transmission is distributed on the upper surface of the carrier, and the other surface is used as the stratum. The connection between the silicon wafer and the carrier can be realized by flip chip technology. When the connection between the silicon wafer and the carrier is completed, the silicon wafer is sealed to prevent mechanical damage. The vias on the carrier play the role of connecting two surfaces and realizing signal transmission. The solder balls are connected to the via pads through a micro-welding process similar to wire bonding to form a solder ball array. The top surface of the carrier is connected with a reinforcing layer through glue, and the reinforcing layer is used for providing rigidity for the package and ensuring the flatness of the package. Usually, the thermal grease is connected to the heat sink on the back of the flip chip, which provides good thermal characteristics for the package. The solder ball composition of TBGA is 90Pb/ 10Sn, and the solder ball diameter is about 0.65mm. Typical solder ball array spacings are 1.0mm, 1.27mm and1.5mm.. The assembly between TBGA and PCB adopts 63Sn/37Pb*** * crystal solder. TBGA can also be assembled by using the existing surface mount equipment and technology and adopting the assembly method similar to CBGA.
The I/O number of commonly used TBGA packages is less than 448, and products such as TBGA736 have been listed. Some large foreign companies are developing TBGA with I/O number greater than 1000.
The advantages of TBGA package are:
① It is lighter and smaller than most other BGA package types (especially those with high I/O number).
② It has better electrical performance than QFP and PBGA packages.
③ Suitable for batch electronic assembly.
In addition, this package realizes the connection between the silicon chip and the carrier in the form of high-density flip chip, which makes TBGA have many advantages such as low signal noise. Because the thermal expansion coefficient TCE of the reinforcement layer in the printed board and TBGA package is basically matched, it has little effect on the reliability of the assembled TBGA solder joint. The main problem of TBGA packaging is the influence of moisture absorption on packaging.
The problem of TBGA in application is how to occupy a place in the field of electronic assembly. Firstly, the reliability of TBGA must be proved in mass production environment. Secondly, the cost of TBGA packaging must be equivalent to that of PBGA packaging. Due to the complexity and relatively high packaging cost of TBGA, TBGA is mainly used for electronic products with high performance and high I/O number.
2 flip chip:
Different from other surface mount devices, the flip chip is not packaged, and the interconnection array is distributed on the surface of the silicon chip, replacing the wire bonding connection form, and the silicon chip is directly flip-chip on the PCB. Flip-chip no longer needs to lead out I/O terminals from the silicon wafer, which greatly shortens the interconnection length, reduces the RC delay and effectively improves the electrical performance. There are three main types of flip-chip connections: C4, DC4 and FCAA.
2. 1c4 (controlled collapse chip connection controlled collapse chip connection)
Fig. 7 C4 structural form
C4 is a form similar to ultra-fine pitch BGA (see Figure 7). Generally, the pitch of solder ball array connected to silicon wafer is 0.203~0.254mm, the diameter of solder ball is 0. 102 ~ 0. 127 mm, and the composition of solder ball is 97Pb/3Sn. These solder balls can be completely or partially distributed on the silicon wafer. Because ceramics can withstand high reflow temperature, ceramics are used as substrates for C4 connections. Usually, gold-plated or tin-plated connection pads are distributed on the ceramic surface in advance, and then C4 flip-chip connection is carried out.
C4 connection cannot be assembled with existing assembly equipment and technology because the melting temperature of 97Pb/3Sn solder balls is 320℃, and there is no other solder in this interconnection structure with C4 connection. In C4 connection, high temperature flux is printed instead of solder paste missing. Firstly, the high-temperature flux is printed on the pads of the substrate or the solder balls of the silicon wafer, and then the solder balls on the silicon wafer are precisely aligned with the corresponding pads on the substrate. The flux provides sufficient adhesion to maintain the relative position until the reflow soldering is completed. The reflow temperature of C4 connection is 360℃. At this temperature, the solder ball melts and the silicon wafer is in a "suspended" state. Due to the surface tension of solder, the silicon wafer will automatically correct the relative position of solder ball and pad, and finally the solder collapses to a certain height to form a connection point. C4 connection mode is mainly used for CBGA and CCGA packaging, in addition, some manufacturers also apply this technology to ceramic multi-chip module (MCM-C). The number of I/Os connected by C4 is below 1500, and some companies expect to develop more than 3,000 I/Os. ..
Advantages of C4 connection are:
1) has excellent electrical and thermal properties.
2) The I/O number can be very high when the pitch of solder balls is moderate.
3) Not limited by the size of the pad.
4) It can be suitable for mass production.
5) The size and weight can be greatly reduced.
In addition, C4 connection has only one interconnection interface between the silicon chip and the substrate, which can provide the shortest and least interference signal transmission channel. The reduction of the number of interfaces makes the structure simpler and more reliable. There are still many technical challenges in C4 connection, and it is still difficult to really apply it to electronic products. C4 bonding can only be applied to ceramic substrates, and it will be widely used in products with high performance and high I/O number, such as CBGA, CCGA, MCM-C and so on.
2.2 DCA (direct chip connection direct chip connection)
Similar to C4, DCA is an ultra-fine pitch connection (see Figure 8). The silicon wafer in DCA has the same structure as the silicon wafer in C4 connection, and the only difference between them is the choice of substrate, which is a typical printing material. The solder ball composition of DCA is 97Pb/3Sn, and the solder on the connection pad is * * * crystal solder (37Pb/63Sn). For DCA, because the spacing is only 0.203~0.254mm, it is difficult for * * crystal solder to leak to the connection pad. Therefore, before assembly, the top of the connection pad is plated with lead-tin solder instead of solder paste, and the amount of solder on the pad is very strict, usually more than other ultra-fine pitch components. The solder with a thickness of 0.05 1 ~ 0. 102 mm on the connection pad is pre-plated, generally slightly dome-shaped, so it must be leveled before pasting, otherwise it will affect the reliable alignment between the solder ball and the pad.
Figure 8 DCA structure form
This connection can be realized by surface mount equipment and technology. First, the flux is distributed on the silicon wafer by printing, then the silicon wafer is mounted, and finally reflowed. The reflow soldering temperature of DCA module is about 220℃, which is lower than the melting point of solder balls, but higher than the melting point of crystal solder on connection pads. The solder balls on the silicon wafer play the role of rigid support, and the crystal solder melts after reflow, forming a solder joint connection between the solder balls and the pads. For this solder joint formed by two different Pb/Sn compositions, the interface between the two solders in the solder joint is not obvious, but a smooth transition zone from 97Pb/3Sn to 37Pb/63Sn is formed. Due to the rigid support of the solder ball, the solder ball will not "collapse" in DCA assembly, but it also has self-correcting characteristics. DCA has been applied, and the I/O number is mainly below 350. Some companies plan to develop I/O numbers above 500. The driving force of this technology development is not higher I/O number, but mainly focused on the reduction of size, weight and cost. The characteristics of DCA are very similar to C4. Because DCA can be connected with PCB by using the existing surface mount technology, it can be used in many applications, especially in portable electronic products.
However, the advantages of DCA technology cannot be exaggerated, and there are still many technical challenges in the development of DCA technology. There are not many assemblers who use this technology in actual production, and they are all trying to improve the process level to expand the application of DCA. Because DCA connection transfers high-density related complexity to PCB, it increases the difficulty of PCB manufacturing. In addition, there are few manufacturers specializing in the production of silicon wafers with solder balls, and there are still many problems worthy of attention in assembly equipment and technology. Only by solving these problems can we promote the development of DCA technology.
2.3 fcaa (flip chip bonding attachment flip chip bonding connection)
There are many forms of FCAA connection, which is still in the initial stage of development. The connection between the silicon wafer and the substrate is replaced by glue. In this regard, there may be solder balls on the bottom of the silicon wafer, or solder bumps and other structures may be used. The adhesives used in FCAA include isotropic and anisotropic types, which mainly depend on the connection conditions in practical applications. In addition, the choice of substrate usually includes ceramics, printed board materials and flexible printed circuit boards. This technology is not mature at present, so I won't elaborate here.