The pure gold wire is drawn from a material with a gold purity of 99.99% or more, which contains trace elements such as Ag/Cu/Si/Ca/Mg. The silver thread is drawn from a material with a purity of silver of 99.99% or more, and it also contains other trace elements. However, in order to reduce costs, some LED manufacturers have developed copper alloys, gold-clad silver alloy wires, and silver alloy wires to replace expensive gold wires. The following is how to identify whether the gold wire used in LED packaging products is pure gold from Shenzhen Xinguangshuo Technology:
Chemical composition inspection
Method 1: EDS component detection
(Identify incoming material types: gold wire, silver wire, gold-coated silver alloy wire, copper wire, aluminum wire.)
Gold wire has the advantages of high electrical conductivity, good thermal conductivity, corrosion resistance, good toughness, and excellent chemical stability. However, the price of gold wire is expensive, which leads to high packaging costs. In the periodic table, the four metal elements of gold, silver, copper and aluminum in the transition group of metal elements have high electrical conductivity. Many LED manufacturers try to develop materials such as copper alloys, gold-clad silver alloy wires, and silver alloy wires to replace expensive gold wires. Although these alternatives are superior to gold wires in some properties, they are much worse in terms of chemical stability. For example, silver wires and gold-coated silver alloy wires are susceptible to sulfur/chlorine/bromination corrosion, and copper wires are prone to oxidation. In the case of encapsulated silica gel similar to water-absorbent and breathable sponge, these alternatives make the bonding wire vulnerable to chemical corrosion, reduce the reliability of the light source, and use it for a long time, and the LED lamp beads are easy to break and die.
Method 2: ICP purity detection
(Identify the purity level of the gold wire and determine the added alloying elements.)
The LED bond alloy wire is drawn from a material with a gold purity of 99.99% or more, which contains trace elements such as Ag/Cu/Si/Ca/Mg. By designing a reasonable alloy composition, the gold wire has the advantages of sufficiently high tensile and bonding strength, good ball formation, and low vibration fracture rate. Most of the bond alloy wires should be high-purity alloy wires with a purity of 99.99% or more, and the total amount of trace elements should be kept below 0.01% to maintain the characteristics of gold.
Diameter deviation
One gram of gold can draw a gold wire with a length of 26.37m and a diameter of 50μm (2 mil), or a gold wire with a length of 105.49m and a diameter of 25μm (1 mil). If the length of the gold wire is fixed, and if the diameter of the incoming gold wire is half of the original, the resistance measured on the gold wire is one-fourth of the normal.
Jinjian Testing pointed out that for suppliers, the smaller the diameter of the gold wire, the lower the cost, and the higher the profit when the price remains unchanged. For LED customers who use gold wires, purchasing gold wires that cut corners on the diameter will increase the resistance of the gold wires and reduce the risk of fusing current, which will greatly reduce the life of the LED light source. The life of the 1.0 mil gold wire must be shorter than that of the 1.2 mil gold wire, but the simple inspection of the packaging factory cannot be tested. Here, Jinjian can provide the incoming material inspection of the gold wire diameter.
Surface quality inspection
The surface of the wire should be free of nicks, pits, scratches, cracks, bumps, folds, and other defects that reduce the service life of the device that exceed 5% of the wire diameter. During the drawing process of the gold wire, the surface defects on the wire surface will increase the current density and make the damaged part easily burned. At the same time, the resistance to mechanical stress is reduced, causing the damage of the inner lead to break.
The surface of the gold wire should be free of oil, rust, dust, and other adherents, which will reduce the bonding strength between the gold wire and the LED chip, and between the gold wire and the bracket.
Mechanical performance testing (breaking load and elongation)
A good gold wire that can withstand the impact generated during resin encapsulation must have a specified breaking load and elongation. At the same time, the breaking force and elongation of the gold wire play a key role in the quality of wire bonding, and bonding wires with high breaking rate and elongation are more conducive to bonding.
Too soft gold wire can cause the following disadvantages: ①The arch wire sags; ②The ball is unstable; ③The neck of the ball is easy to shrink; ④The gold wire is easy to break.
Too hard gold wire will cause the following defects: ①Put the chip electrode or epitaxial hole; ②The neck of the gold ball is broken; ③It is difficult to form an alloy; ④It is difficult to control the arc of the arch wire.
