Testing the quality of the coating is an important means of checking the quality of the plating. Jinjian detection LED bracket silver plating layer inspection project includes the base material of the bracket, the quality of the coating, the thickness of the coating and the uniformity inspection.
1. Identify the base material of the bracket
At present, there are iron brackets, aluminum brackets, brass brackets, copper brackets, etc. The aluminum brackets are the cheapest, then brass, and finally copper. Iron brackets have the lowest thermal conductivity, followed by aluminum and brass, and copper is the best. Many packaging factories promise that the bracket is copper, which is actually brass or adulterated copper.
The effects of different material brackets on LED performance are also different, especially for light fading. This is mainly because the thermal conductivity of copper is much better than that of iron and aluminum. The thermal conductivity of copper is 398W (mk), while the thermal conductivity of iron is only about 50W (mk), which is only 1/8 of the former.
2. Identify the quality of the plating
A good plating layer should be fine, smooth, uniform and continuous. It does not allow contaminants, chemical residues, spots, black spots, charring, roughness, pinholes, pitting, cracks, delamination, foaming, and Defects such as wrinkling of the skin, peeling of the coating, yellowing, crystalline coating, and partial plating.
3. Measure the thickness and uniformity of the stent plating
The existing LED light source on the market selects copper as the base material of the lead frame. In order to prevent oxidation of copper, the surface of the stent is usually plated with a layer of silver. If the silver plating layer is too thin, the stent is liable to yellow under high temperature conditions. The yellowing of the silver-plated layer is not caused by the silver-plated layer itself, but by the copper layer under the silver layer. At high temperatures, copper atoms diffuse and penetrate the surface of the silver layer, causing the silver layer to yellow. The oxidizability of copper is the biggest drawback of copper itself. When copper is oxidized, thermal and thermal performance will be greatly reduced. Therefore, the thickness of the silver plating layer is crucial.
At the same time, both copper and silver are susceptible to corrosion by various volatile sulfides and halides in the air, causing darkening of the surface. Studies have shown that discoloration increases the surface resistance by about 20-80%, and the power loss increases, so that the stability and reliability of the LED are greatly reduced, and even lead to serious accidents.
In addition, customers can also use the following incoming inspection methods to select reliable materials:
1. Appearance inspection: visual method, magnifying glass (4~10 times).
2. Silver plating adhesion test: bending method, tape method or combined use.
3. Soldering test: Dip tin method, generally more than 95% of the tin area is even and smooth.
4. Water Vapor Aging Test: Test for discoloration or corrosion spots and subsequent weldability.
5. Anti-tarnish test: use oven baking method, whether it is discolored or peeled.
6. Corrosion resistance test: salt spray test, nitric acid test, sulfur dioxide test, hydrogen sulfide test.
LED bracket plating quality impact on LEDs
Attached:
LED silver plating basic process
Degreasing - Washing - Polishing (grinding) - Activation - Washing - Front Nickel - Washing - Alkali Copper - Washing - Acid Copper - Washing - Post Nickel - Washing - Pre-plating Silver - thick silver (optional silver plating) - washing - peeling silver - washing - electrolysis - washing - silver protection - washing - baking - receiving packaging
case analysis:
A customer's in-line lamp beads have a dead light phenomenon in reflow soldering, and the gold detector is commissioned to analyze the cause of the dead light. The phenomenon of reflow soldering dead lamp is analyzed because the silver plating layer of the bracket wire bonding platform is thin, so that the bonding force between the two solder joints and the bracket is weak, so that the welding of the two solder tails is weak, and during the reflow soldering process, the solder joints are hot and cold. It is easy to separate from the bracket after shrinking. Therefore, Jinjian advised customers to strengthen the inspection of the silver plating of the LED bracket.
After the failure lamp was dissolved in the tube, it was observed under a scanning electron microscope. The second welding fish tail was broken, and the fish tail and the support were hardly contacted, and there was a phenomenon of virtual welding.
Under the scanning electron microscope, it was observed that the silver plating layer of the two-welded stent was too thin and uneven, the thick silver plating layer was about 1.32 um, and the thin silver plating layer was only 0.56 um. The silver plating layer is too thin and the thickness is uneven, which may cause the adhesion of the solder joint to be weak, and the detachment from the bracket causes the LED to die.
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