In addition to the above, three additional points are added:
1.Gold wire characteristics.
In addition to the above advantages, gold wire has a face-centered cubic lattice structure, in its structure because of defects, dislocations and vacancies and so on make the lattice incomplete, due to these incompleteness and the physical properties of the gold wire are affected, gold wire is more brittle and easier to break after processing. However, the properties of the annealed gold wire are relatively stable, because annealing can reduce the stress, make the gold wire soft, not easy to break, and at the same time, in the annealing process, the gold wire expands slightly, often making it very straight, just suitable for use. The annealing atmosphere is not demanding, vacuum or N2 filling is feasible, as for the temperature at 400 450.
2.The reason for "off-key".
The bonding of aluminum metallization film and gold wire is prone to produce brittle intermetallic compounds, which cause discontinuous cracks and voids between them due to the very strong stress between them, resulting in a complete open circuit at the bonding point or the interruption of electrical contact. Scanning with an electron microprobe has shown that the fracture failure is related to the gold-rich phase.
Bond failure is caused by white intermetallic compounds (Au2Al), known as "white patches". Because the "white spots" are not only brittle but also have low conductivity, which increases the contact resistance, microscopic examination shows that the discontinuities enter the intermetallic band near the middle thickness. A simple way to prevent a gold-aluminium reaction is to evaporate a diffusion-blocking metal (e.g., molybdenum) between the aluminium film and the gold bond, or to use a gold-gold bond.
The main reason for the debonding of the gold-aluminum system is the formation of "white spots", and the debonding of the aluminum-aluminum system is also due to the growth of a white loose substance around the solder joints (especially the soldering points of the gold plating layer) - aluminum hydroxide (commonly known as "white hair"), which is more obvious after the humidity test. Poorly sealed devices have "white hairs" on the surface of the aluminum wire, which is a loose and insulating substance.
3.Precautions for titanium powder method.
In the titanium powder method, because the reaction between titanium and hydrogen at high temperature and low pressure (such as under vacuum) is reversible, titanium hydride decomposes titanium, and if the amount of hydrogen is too large, titanium and hydrogen will be violently combined, so it cannot be roasted in hydrogen.
When sintered, titanium runs into the glass phase of the ceramic and reduces the glass viscosity. As a result, the glass flows out freely and slightly, combining the ceramic with the metal pieces. After high-temperature sintering, a thin layer of copper or nickel film is added with electroplating or electroless plating.
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