Date: 2019-12-26
In recent years the rapid development of the panel industry, after the domestic manufacturers crazy expansion, the product supply and demand relationship has been basically relaxed, manufacturers began to focus on the product "quality" to improve.
The display panel industry is moving toward high-resolution graphics, curved surfaces, ultra-thin surfaces, thinness, bendability, high dynamic HDR, high contrast and wide color games. the mini-led is born.
According to the forecast, the mini-led will officially break out in 2019 and enter the commercialization stage.
At present, the global mainstream manufacturers have basically completed the research and development process of mini-led backlight, and entered the stage of small batch samples or large batch supply.
Domestic enterprises are also in the process of intensive research to speed up the process of market.
Mini-led USES LED chip sizes in the micron scale, and each mini-led circuit board typically has thousands of chips and tens of thousands of solder joints to connect to the RGB tri-color chip.
Such a huge amount of solder joints, to the chip package welding brought great difficulty.
Today we are going to learn about the welding process.
Compared with the traditional reflow welding process, Mini- LED technology requirements to the extreme, according to statistics, more than 40% of the welding defects are caused by the printing process, 40% is caused by welding.
Other 20% and solder paste, substrate materials have a lot to do.
For the reliable welding of mini-led, higher requirements are put forward for reflow welding of equipment, welding process and materials (solder paste), all of which are indispensable.
Equipment - vacuum reflow welding:
The mini-led has smaller solder pads, less solder paste and smaller chips, which puts forward higher requirements for welding equipment, temperature uniformity and other technological parameters.
Current welding problems include:
1. Chip displacement: there is movement after welding of the chip, so it is necessary to reduce the movement after welding of the bare chip.
2. Chip rotation: because the spacing of the mini-led chip itself is only 0.8mm, 0.6mm, 0.4mm or less, the chip itself is easy to rotate in the atmosphere during the welding process, which has a bad influence.
3. High void rate: currently, after nitrogen reflow welding, low void rate solder paste is used, and the void rate is controlled to about 10% after welding.
With ordinary solder paste, the void rate may reach more than 15% after welding.
High void rate, long-term use due to thermal conductivity or reliability problems may lead to poor product.
4. virtual welding: in the selection of reflow welding, oxygen content is a very important indicator, if the oxygen content can not be controlled to within 100ppm, or even lower, it may lead to virtual welding of the product.
At the same time, the temperature uniformity is not up to standard is also a very important factor.
If the temperature uniformity in the whole furnace chamber is less than 2 degrees, it will lead to some of the chip virtual poor welding.
These problems are also important parameters for users to choose vacuum welding furnace.
Must go testing more, must control technical index strictly.
After all, with more than 9,000 chips on a single circuit board, it's a big deal to have a few bugs that lead to bugs in the final product.
These problems are also important parameters for users to choose vacuum welding furnace.
Must go testing more, must control technical index strictly.
After all, with more than 9,000 chips on a single circuit board, it's a big deal to have a few bugs that lead to bugs in the final product.
Vacuum return furnace at MINILED
The author is a test industry reflow and vacuum reflow furnace, many times failed, after more than a year to test the success of the feeling. The detour ahead is too long.