Heraeus Electronics-Song Jianbo.
Summary:
According to different application scenarios, semiconductor devices can usually be divided into four categories: consumer electronics, industrial-grade electronics, automotive electronics, and military products. At present, consumer electronics and industrial-grade electronics on the market are mainly copper wires or palladium-plated copper wires, gold-palladium-copper wires, and automotive electronics are still dominated by gold wires. With the recovery of the automobile market, especially the hot new energy vehicle market, the demand for electronic components is also increasing day by day, and the requirements for their reliability are getting higher and higher.
The so-called "automotive-grade components" need to pass AEC-Q certification, for example, AEC-Q100 is suitable for IC products, AEC-Q101 is suitable for discrete devices, and AEC-Q102 is suitable for optoelectronic devices. Among them, AEC-Q100 contains 4 grades, G0 is the highest, G3 is the lowest, and the specific reliability items and conditions corresponding to different grades are listed in the following table:
Table 1 *r181: automotive grade 0 - pcb and assembly recommendations
With the demand for high reliability of automotive electronic devices, higher requirements are also put forward for the packaging materials inside them. Here, we will:High reliability gold wireto see how it meets the needs of high-reliability devices.
Before introducing the product, let's take a look at some of the key properties of gold wire, one of which is the heat-affected zone.
Figure 1Description of the key characteristics of the gold wire.
Heat-affected zoneIn the process of ball burning, the high temperature will melt the gold wire to form Fab, and in this process, the heat will be conducted along the direction of the line, so that the grain structure of the gold wire close to the Fab area will change, become thicker, and the wire will become softer. This part of the area is called HAZ, which is usually tens to hundreds of microns in length. HAZ is a very important feature of gold wire, it directly affects the arc ability of the wire, usually the shorter the HAZ gold wire can be made of lower arc height, suitable for low arc, long arc applications.
Figure 2Description of the heat-affected zone.
From the perspective of wires, different doping types and contents will affect the length of HAZ.
Why does the type of doping affect the formation of HAZ?The main reason is that the recrystallization temperature of different doping elements is different, for example, Ca doping will make the recrystallization temperature of the ball neck greater than 300°C. Therefore, even if it is a 4N gold wire, there will be different lengths of HAZ due to different types of doping.
The length of the HET part of the gold wire type HAZ is listed in Table 2 below. As can be seen from the following data, there will be a slight difference in the length of the HAZ under the condition of different FAB sizes, usually the FAB size is larger, and the HAZ will be longer, the main reason is that when the large ball is burned, the FAB needs more heat to melt the wire, and the large heat will make the ball neck change more significantly, which will increase the length of the HAZ. Therefore, if the problem of ball neck crack is found in the WB process, you can consider appropriately reducing the ball burning parameters to improve the strength of the neck.
Table 2Comparison of the length of the gold wire HAZ of different models.
First solder joint:Its shape, hardness, alloying elements, etc. will affect the bond with the pad surface, especially the reliability.
Table 3 below shows the reliability performance of commonly used wires after combining with Al Pad, among which the growth rate of Au Al IMC is faster, which mainly depends on the atomic valence state, atomic radius, diffusivity and other factors of the material. If one atom spreads faster than the other, it will leave gaps behind it, which clump together to form themOkendall HollowIf such cavities are connected together, the ball will fall off, causing the product to fail in the open circuit.
Figure 3 shows the Au AL 150 IMC layer after 1000 hours of storage**, so if you want to increase the high-temperature storage capacity of the gold wire, you need to delay the growth rate of the Au AL IMC.
Table 3Reliability performance of different materials combined with Al.
Figure 3Au and Al IMC form the Kirkendal hole (150 1000h).
In response to this situation, HET has a good product to recommend to customers, product name:
Chemical composition
Gold content: 99%.
Description of the basic features of the product:
Excellent first-solder joint reliability.
Halogen-free, suitable for frame and substrate applications.
Fab is soft and has good coaxiality, especially suitable for small pitch products.
The fine wire has high strength and is suitable for projects with reduced wire diameter.
Let's take a comprehensive look at this gold wire from the aspects of Fab hardness, spherical shape of the first solder joint, process window of the second solder joint, and the ability of high-temperature storage.
Fab Hardness:Relmax will be softer than the same type of gold wire, and the impact on the pad will be smaller, which will effectively protect the pad from damage.
Figure 4Fab hardness comparison (15 m wire diameter, 25 m Fab).
The first solder joint is spherical:The concentricity of RELMAX will be better, and it is not easy to have abnormalities such as eccentric balls, which is especially suitable for product applications with small pad fenestration.
Figure 5Spherical coaxiality contrast.
Second solder joint process window:The process window of Relmax is significantly larger, and FP2 here is another 2N gold wire of HET, which has a higher hardness, resulting in a smaller process window for the second solder joint.
Figure 6Comparison of the second solder joint process window (1mil gold wire, BGA).
High Temperature Storage Reliability:After high temperature storage, the tensile test was carried out, and the test site was the neck of the ball, and the result showed 08mil 175 10000h did not show the ball falling off;Another set of 06mil 200 5000h is also no problem.
Figure 7Tensile test (0.)8mil，bga 1μm alsi1%cu0.5% pad）
Figure 8175 stores 1000h IMC
Figure 9Tensile test (0.)6mil，bga 1μm alsi1%cu0.5% pad）
Figure 10Relatively stable IMC, 5000h with only slight voiding.
Why does Relmax gold wire improve reliability?In the high-temperature storage stage, a PD barrier layer will be formed with the passage of time, which delays the diffusion rate between Au Al and inhibits the continued diffusion of Au Al to the Au Al IMC layer, thereby improving the ability of high-temperature storage. Referring to the following EPMA analysis results, it can be clearly seen that the PD layer is distributed between the Au and AUAL compounds.
Figure 11EPMA analysis, the distribution of the PD layer was detected.
Figure 12PD Hindrance Layer Action (schematic).
Summary: Under what application conditions can relmax be chosen?
Small pitch High reliability product application with ultra-small pitch.
Products that require high reliability while reducing wire diameter.
Low K and chip-sensitive product applications.
It is suitable for projects where 4N gold wire is converted to 2N gold wire.
Improved MTBA for 2N gold wire.
At present, this product has been stably mass-produced in the industry, welcome to consult. Heraeus Electronics, with its strong R&D strength and continuous R&D investment, will provide our customers with more excellent bonding wire products and help the sustainable development of traditional packaging