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Gold welding process
Gold and gold alloys have good weldability and brazeability. For pure gold, oxidation during soldering, brazing, and brazing is not a serious problem. However, some of its alloys must be protected from oxidation during the welding process. Gold and most of its alloys have a low melting temperature (1093 ° C) and good oxidation resistance, so they are easy to weld. The following is a brief introduction to several gold welding processes:
First, gas welding
Generally, micro-reducing oxygen-acetylene flame is used for gas welding to avoid pores. Coal gas - oxygen gas - air flame may also be employed. Gas welding is usually done with a small torch. In order to match the weld metal color masterbatch, it is common to use the same gold or gold to fill the metal. When not welding flux can also be used borax or boric acid, or mixtures thereof.
Second, arc welding
Tungsten argon arc welding, plasma arc welding, laser welding and vacuum electron beam welding can be used to weld gold and gold alloys. These methods have fast welding speed and good welding quality, and are especially suitable for welding alloys which may cause oxidation and discoloration at high temperatures. . Take care to prevent tungsten contamination when using tungsten argon arc welding. The filler metal composition must be similar to the wire.
Third, resistance welding
Resistance welding weldable jewelery, optical instruments and other small electrical contact member of the gold-copper alloy, silver-gold-copper alloy, and a gold-copper-nickel alloy, an electrode made with Mo. The strip members are welded by pulse seam welding; the glasses frame is protected by spot welding with argon and nitrogen.
Fourth, solid state welding
Gold and gold alloys can be cold-welded or thermo-welded due to their good plasticity, and sometimes friction welded.
When using cold pressure welding, it must be noted that the surface of the weldment before welding is clean, and when the deformation exceeds 20%, a firm connection can be achieved.
In the microelectronics technology, the wire ball bonding of the inner lead of the integrated circuit is to melt the gold wire end of the diameter of 20-50 μm into a ball, and then use the hot pressure welding or the ultrasonic hot press welding method to make the gold wire ball and the integrated circuit chip. The connection is achieved by a silicon wafer that is metallized by Au or Ag or Al. This gold wire ball bonding technology has been widely used in microelectronic production technology.
Five, brazing
Brazing of gold and gold alloys is commonly used in gold jewellery and dental products. In order to match the color of the splicing with the brazed components and the need for grading brazing of certain assemblies, the brazing materials listed in Table 1 can be adapted. The color can be adapted to the needs of different melting temperatures.
Table 1 Gold alloy solder
category
chemical composition(%)
Solid line
(°C)
Liquidus
(°C)
Au
Ag
Cu
Zn
other
yellow
10K soft
42
twenty four
16
9
Cd1
630
700
10K hard
42
35
twenty two
1
730
745
14K soft
58
18
12
12
720
755
14K hard
58
twenty one
15
6
775
800
white
10K soft
47
15
35
Sn3
657
775
10K hard
62
17
15
4
Sn2
770
810
14K soft
65
16
15
4
Sn4
740
800
14K hard
82
8
Pd8, Sn2
1090
1105
The complexity of the problem is that the complicated jewelry needs to be welded several times to complete, and the soldering temperature of the latter welding is lower than the previous one. Therefore, it is necessary to form a solder series. For example, some manufacturers' 8K gold solders operate from 700 ° C (first solder) to 640 ° C (third solder), 14K gold solder from 780 ° C (first solder) to 670 ° C (third Solder), 18K gold solder from 820 ° C (first solder) to 700 ° C (third solder).
The solder with high silver content has good wettability and fluidity, and it has less tendency to interact with gold. The solder with high copper content interacts with the base metal when the brazing temperature increases. Intensified. Therefore, the brazing temperature and the holding time must be strictly controlled, and it is generally preferred to perform rapid brazing to prevent the occurrence of corrosion defects.
Gold and gold alloy brazing processes can be flame brazing, electric resistance brazing, conventional furnace brazing, and high frequency brazing. Most of the jewelry and dental industries use neutral or reducing oxygen-acetylene flame brazing; when some small parts are used for resistance brazing, the positioned joints can be placed between the two electrodes, and when heated to the brazing temperature, they are sent to Brazing wire, complete brazing joint.
Dental brazing material, when brazing material to prevent harm to human body, you must disable the cadmium-containing solder, Au-Ag-Pd available type solder, K gold Most copper, black oxide when heated brown, brazing Injection protection should be used. The injection should preferably be a mixture of 50% molten borax, 43% boric acid, and 7% sodium carbonate. A reducing flame must be used for flame brazing.
Sixth, soldering
In semiconductor and microelectronic devices, it is often used as a metallization coating on the surface of ceramics, glass or other metals. For example, a plating of gold in a thin film circuit is used as an electrical conductor (circuit). The soldering of the circuit is carried out according to the usual soldering process, and the Sn61-Pb39 solder can rapidly diffuse and alloy with the gold film. The other two suitable solders are In95-Bi5, Sn53-Pb29-In17-Zn0.5. Brazing is carried out using a suitable heating method and a rosin-type flux. After welding, it is washed in ethanol or a chlorinated hydrocarbon solvent to remove residual flux.
It should be pointed out that when soldering tin -based soldering of gold and gold alloys, the brazing temperature and brazing time must be strictly controlled to prevent the corrosion caused by excessive dissolution, including the “full shedding of the gold layer in the microelectronic film circuitâ€. "phenomenon.
In addition, contact-reactive brazing, which is achieved by eutectic reaction of gold with certain metals, is also used in semiconductor and microelectronic device chip connections. For example, the Au-Si eutectic point is 370 ° C, and Au-Si eutectic bonding is a typical process technology.