Performance comparison of three kinds of processes for preparing stereo LED light

Stereoscopic light-emitting lamps have become a research hotspot, and the key is how to obtain uniform illumination on the front and back. In this paper, we study the transient and steady-state luminous flux, color temperature and chromaticity coordinates of the front and back of the three-dimensional lamp.

The sample obtained by first coating the silica gel and then coating the phosphor paste (sample 2) has the smallest difference between the front and the back, and the color temperature and chromaticity coordinates are close to each other; while the direct coating of the phosphor (sample 1) has the largest total luminous flux. However, the color temperature, color coordinate and luminous flux of the front and back sides are very different; the light source prepared by coating the silica gel doped with the diffusion powder and then coating the phosphor has the lowest total luminous flux, and the difference between the front and back luminous flux is larger than that of the sample 2.

The illuminating angles of the three samples were tested, and the illuminating angle distribution was similar, and the illuminating intensity was similar to the luminous flux ratio of the integrating sphere test. Therefore, the preparation process of the sample 2 is suitable for preparing a three-dimensional light-emitting lamp.

introduction

The market-oriented LED packaging technology is that the positive-loading chip is fixed in the concave cup by insulating glue or silver glue, and the positive and negative electrodes are connected through the gold wire, and then the silica gel mixed with the phosphor powder is placed on the upper point, and the white light is generated after being lit. .

There are three disadvantages to this product:

1. The gold wire is easily broken by the thermal expansion and contraction of the silica gel;

2. The shape of the silica gel affected by the gold line curvature affecting the mixed phosphor is difficult to control, resulting in uneven distribution of the phosphor;

3. The chip is grown on a sapphire substrate. The thickness of the chip is about 8 μm, and the thickness of the sapphire is about 150 μm. The heat of the chip is transmitted to the support through the sapphire. The path is long and the thermal resistance is large, and the heat dissipation performance is poor.

The appearance of flip chip can effectively solve the above problems. The package of flip chip is commonly called gold-free package. There is no gold wire to effectively solve the first and second problems. At the same time, the flip chip layer is directly bonded to the substrate, sapphire. It is no longer used as a heat conduction channel, but as a luminescent medium, it avoids the problem of long heat conduction path and poor heat dissipation performance.

The advent of flip-chips has made planar coating technology available for LED packaging. Flat coating technology is generally used for semiconductor component packaging processes. There is no report of planar coating technology for LED packaging processes.

In this paper, the flip-chip package on a flat-coated white ceramic substrate is studied, and the front and back light distributions of the three-dimensional illumination are studied. The planar coating process with uniform light color is improved, and the optimal preparation of the stereoluminescent phosphor coating technology is obtained. .

experiment

The flip-chip LED chip is fixed on the white ceramic substrate by a die bonder. The size of the ceramic plate is 5 mm×8 mm×0.64 mm, and the size of the chip is 14 mil×30 mil. The sample after the chip is fixed is shown in FIG. 1 , and the glue and The phosphor ratio was: 1.1:1.1:1.28:0.095, labeled as Sample 1, Sample 2, and Sample 3.

Sample 1 is a flat phosphor coated directly on the front side;

Sample 2 is first filled with silica gel to fill the inter-chip gap, dried and then coated on the front side with a glue plane of mixed phosphor;

Sample 3 was first coated with interstitial voids coated with silica gel mixed with diffusion powder, dried and then coated on the front side with a glue plane of mixed phosphor, as shown in FIG.

Test equipment: The light color test was carried out on the front and back sides of the standard machine (model 0.3m integrating sphere); the light distribution was tested and analyzed by a remote distributed photometer.

Figure 1: Uncoated phosphor white ceramic plate after solid crystal

Figure 2: Photographs of Sample 1, Sample 2 and Sample 3