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Analyze the semiconductor package supported by the copper ball
In recent years, flat-panel and smart phones have rapidly expanded in the market with high popularity. With the high-performance requirements of the public, high-density packaging technology is also being pursued. In order to achieve high performance and high density, it is expected that the size of CSP will become thinner and thinner. I am also looking forward to the emergence of new technologies and new materials such as 3D encapsulation and large WL-CSP. Senju Metal Industry also responded to these requirements and prepared many welding consumables for different purposes and uses, published in SEMI Taiwan.
The so-called 3D package is a PKG and electronic part that is joined upwards in a longitudinal manner, and the substrate and parts will be back and forth in a reflow oven at approximately 250 ° C. As a result, since the ball is melted and the load is excessively heavy, there is a possibility that an electric short circuit occurs due to contact between the ball and the ball. In response to this issue, Senju Metal proposed a copper nucleus ball that can ensure space. The copper ball as the core of the copper core ball has a melting point of about 1,080 ° C, that is, it returns back and forth in the reflow agent, and the shape of the copper ball does not change, so that a certain space can be reserved for the 3D package. Moreover, the copper pillars that must be used in general electroplating engineering can also be changed into copper core balls, and the packaging process can be performed by using existing equipment.
The copper core ball is a composite multi-layer structure solder ball composed of a copper ball, a nickel plating layer and a tin plating layer.
The M758 with thermal fatigue resistance is more sturdy to the Chip and is the most suitable material for WLCSP.
With high-performance, high-density packaging, the size of the Chip will become increasingly thinner and larger. When the substrate is bonded to Si having a small coefficient of thermal expansion, the electrode and the ball are in contact with each other due to the difference in thermal expansion coefficient, which may cause damage or even defects. For this problem, Senju Metal Industry developed the M758 as a solution.
M758 adds Bi and Ni to the Sn-3Ag-Cu series, strengthens and strengthens the structure through solid solution strengthening and precipitation strengthening, and the joint between the substrate and the Chip is stronger. The heat-resistant fatigue property is the most suitable for WLCSP. Used croquet material.
Due to the characteristics of the mobile device, the demand for the impact of falling, and the increase in the area of ​​the battery to be mounted, in the circuit part, the need for high-density packaging increases the thermal fatigue resistance of the surrounding parts. In order to meet the above requirements, Senju Metal has developed the Ryukyu M770 which has both thermal fatigue resistance and drop impact resistance.
In general, cracks due to thermal fatigue are generated when the weld is expanded, and cracks caused by the drop impact characteristics are generated at the joint between the weld and the PKG. If fatigue resistance is pursued, it will reduce its impact resistance and vice versa. If you want to have the resistance to falling impact while having thermal fatigue resistance, the methods of various approaches are mutually different, and it is really difficult to take countermeasures.
In response to this problem, the content of Ag can control the flexibility of the solder joint, and the adjustment of the Ag content is a state suitable for fatigue resistance. Generally, in the surface treatment of PKG, the main component Sn in Cu, Ni and lead-free soldering is very easy to react, and the alloy layer of a considerable thickness is produced. However, after adding Cu and Ni, the alloy layer of the joint surface can be suppressed. The reaction produces a thin metal. When the M770 is subjected to a drop impact, it can prevent the occurrence of cracks by mitigating the impact of the joint interface between the solder fillet and the substrate. In the thermal shock test, the possibility of cracks in the expansion of the weld bead can also be reduced.
Based on the demand for multi-capacity, not only the size required by PKG is small and space-saving, but also the need to be a clean-free product while pursuing the need for a small chip in the Ryukyu package. Therefore, in the selection of flux Quite important. Senju Metal has developed WF-6317 and MB-T100 with excellent wettability, low volatility and detergency, DELTALUX FLUX901K series that does not need to be cleaned after packaging, and reinforcement with flux residue as joint, and with Underfill A good compatibility of the Joint Protect Flux JPK8, etc., is used in fluxes for various applications.
Senju Metal proposes various solutions for different topics in semiconductor packaging.