How to identify whether SMD LED CHIP is pure gold wire
The gold wire used for packaging LED lamp beads has a gold content of more than 99.99%. The gold of this material is produced by a wire drawing process. In addition to 99.99% gold, this gold also contains 1% or less of other elements. trace elements. One of the core components of the LED lamp bead package is the gold wire. The gold wire is the bridge connecting the light-emitting chip and the solder joint, which plays a decisive factor in the service life of the LED lamp bead. So how to identify the purity of gold wire?
Identification of LED gold wire can use ICP purity detection method, mechanical property detection method, and EDS component detection method to determine the purity of LED gold wire
Gold wire purity grades can be identified using ICP purity testing to determine added alloying elements.
1. Looking at the appearance of the gold wire of the LED lamp bead, first of all, there should be no nicks, pits, scratches, cracks, bumps, discounts and other defects that reduce the service life of the device that exceed 5% of the wire diameter on the surface of the gold wire. During the drawing process of the gold wire, the surface defects on the surface of the wire will lead to an increase in the current density, making the damaged part easy to be burned, and at the same time, the ability to resist mechanical stress is reduced, causing the inner lead to break at the damaged part. Secondly, the surface of the gold wire should be free of oil, rust, dust and other adhesions, which will reduce the bonding strength between the gold wire and the LED chip, and between the gold wire and the bracket.
2. There is a diameter deviation between the special gold wire for LED lamp beads and the unqualified gold wire. 1 gram of gold can draw a gold wire with a length of 26.37m and a diameter of 50μm (2 mil), or a length of 105.49m. , A gold wire with a diameter of 25 μm (1 mil). The length of the gold wire is fixed. If the diameter of the incoming gold wire is half of the original, then the measured resistance of the gold wire to be beaten is a quarter of the normal value. For gold wire suppliers, the thinner the diameter of the gold wire, the lower the cost, and the higher the profit when the selling price remains the same.
For LED lamp bead customers who use gold wires, purchasing gold wires that cut corners in diameter will have the risk of increasing the resistance of the gold wire and reducing the fusing current, which will greatly reduce the life of the LED lamp bead light source. The life of 1.0mil gold wire is necessarily shorter than that of 1.2mil gold wire, but the simple inspection of the packaging factory cannot be tested, and the diameter of the gold wire can only be detected with precision instruments.
3. The special gold wire for LED lamp bead is drawn from a material with a gold purity of more than 99.99%. By designing a reasonable alloy composition, the gold wire has high enough tensile force and bonding strength, good sphericity, and vibration fracture rate. low advantage. Most of the bonding wires should be high-purity alloy wires with a purity of more than 99.99%, and the total amount of trace elements (such as Ag/Cu/Si/Ca/Mg) should be kept below 0.01 to maintain the characteristics of gold.
Using mechanical property testing, that is, testing the breaking load and elongation of the gold wire
A good gold wire that can withstand the shock of 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 the bonding wire with high breaking rate and elongation is more conducive to bonding.
Too soft gold wire will cause: ① the arch wire sags; ② the spherical shape is unstable; ③ the ball neck is easy to shrink; ④ the gold wire is easy to break.
Too hard gold wire will lead to: ① the chip electrode or epitaxy is punched out of the hole; ② the neck of the gold ball is broken; ③ it is difficult to form an alloy; ④ it is difficult to control the arc of the arch wire.
Use chemical composition test - EDS composition test method
Identify the types of incoming materials: gold wire, silver wire, gold-clad 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, but the price of gold wire is expensive and the packaging cost is also too high.
