LED package substrate with small light-emitting high-density density trend

　　　　 The small illuminating surface is easier to match the secondary optics, resulting in a higher center light intensity, resulting in a trend toward small package high power density LEDs. The high power density places great demands on the heat dissipation of the package substrate/packaging process/chip/application end. The small-outlet LEDs are generally of two types: SMD and COB surface light sources.

Need to explain here, COB is the abbreviation of chips on board, high-power density SMD light source is actually COB package. (Small history: Today's COB nicknamed the surface light source when it was born, but in an academic exchange organized by the Guangzhou Science and Technology Bureau, the speaker specifically mentioned that the surface light source is different from the popular packaging technology at that time, using COB. Encapsulation. Perhaps the COB feature is obvious and easy to catch up, which is popular.)

Package substrate under the trend of small light-emitting high-density density

High-light-pass density SMD substrate possible popular size 3535/5050/7070/9090

CREE high optical density SMD substrate power density

From the table, the power density per square centimeter of the SMD substrate reaches 24W/cm2 or more.

Small light surface high light flux density COB

The power density of the COB substrate reaches 6W/cm2 or more, and Cree's 2590 is 14.5W/cm2;

From the table and the report, the LES of each manufacturer of the small-glossy high-gloss light is roughly the same, which is 6mm/8.5mm-9mm/11mm-12mm/13mm-14mm/19mm. The power density of the illuminating surface is between 28-40W/cm2, which is more than twice the power density of ordinary COB;

Boldly predict that the future COW surface light source market below 10W will be attacked by SMD; the power density of COB surface light source will also increase as fast as SMD. After all, single high power is its advantage.

High power density package substrate should meet

1 high thermal conductivity

2 high light efficiency

3 chip and substrate thermal expansion coefficient is similar, to avoid thermal damage to the chip damage

4 antioxidant and anti-vulcanization

5 is best thermoelectric separation, mainly for SMD. Thermoelectric separation will greatly facilitate the application side

6 high insulation, mainly for COB surface light source, compliant with high voltage and small current non-isolated drive trend

Various types of package substrate data

Compared with high power density SMD, metal based / SiC / AlN can meet the heat flux density requirements, but metal based and SiC are conductors, not suitable for positive and negative pads require via type SMD package substrate, AlN Excellent thermal conductivity and insulation properties are the most suitable high power density package substrates;

Compared to high power density COB, mirror aluminum/AL2O3/SiC/AlN meets heat flux requirements. Due to the light-emitting efficiency and high cost of SiC/AlN, mirror-surface aluminum-based and Al2O3 ceramics are most suitable for small-emitting high-gloss COB package substrates;

Mirror aluminum and Al2O3 ceramics are the two main streams of COB packaging. It should be noted that although the thermal conductivity of mirror aluminum is much higher than that of ceramics, its thermal expansion coefficient of more than 20 must account for its thermal stress on the chip substrate at high power density.

There are also two kinds of Al2O3 ceramic substrates, one is a sintered silver ceramic substrate with a thick film process, and the other is a DPC (ceramic direct copper-clad) ceramic substrate with a rising film process.

DPC is loading COB substrate

Sintered silver formal COB substrate

The sintered silver ceramic substrate and the DPC ceramic substrate still have great differences. The biggest difference is that the DPC substrate does not contain silver, does not oxidize and vulcanize, and the lumen maintenance rate is much better than that of the sintered silver substrate; the package wire tension is better than that of the sintered silver substrate; Because the solder has a good affinity for silver, the soldering iron has a slightly longer residence time when soldering the silver pad. It is very likely that the silver is adsorbed by the solder and the pad is removed. The solderability of the DPC pad is far better, and the deficiency of the DPC substrate is the initial light. It is not as effective as a sintered silver substrate, and the cost is slightly higher.

DPC achieves the adhesion, the process results are different, the process is proper, and the adhesion force is very strong.

As shown in the pull test, you can see that the ceramics are pulled up.

Exposed to the air for one month, the sintered silver substrate has been severely oxidized

The DPC line uses a thin film process that can be very fine and is suitable for package substrates for flip chip.

DPC fine line spacing 75um

DPC flip-chip COB substrate

In the future, COB in flip-chip package or COB in vertical structure chip package will be more suitable for COB light source with high light transmission and small light output!

Wonderful application of DPC:

Thick copper high power package substrate