PCBA Tech - SMT patch LED lamp beads purchase and quality control

SMT SMD LED lamp beads are light-emitting diodes. They are a type of decorative lighting products often used in the commercial and home lighting industries. They not only have the lighting effect, but also because their light is relatively soft, they are used for interior decoration. To a certain extent, it can also adjust people's mood and relieve people's pressure. Since the types and types of SMT LED lamp beads on the SMT market are very diverse, attention should be paid to details during the purchase process.

1. The brightness of LED lamp beads

Different colors of LED lamp beads will have different luminous intensities, and the common units are mcd and lm, that is, millicandela. The higher the value, the greater the luminous intensity, that is, the brighter. This is an important indicator for selecting LED lamps. The higher the brightness requirement, the more expensive the lamp, because the high-brightness LED chip is more expensive.

2. The color of the LED

There are many small packaging factories that do not have a spectroscopy and color separation machine, so it is difficult to guarantee the quality. LEDs that have not undergone color separation have poor color consistency, and of course the price difference is relatively large.

3. LED chip

The chip origin determines the price and also determines the quality of the lamp. Customers can often determine the quality of the LED lamp by understanding the LED chip supplier used in the LED lamp, because the biggest factor in determining the price of the LED is the chip. Therefore, knowing the chip supplier can roughly determine the price range of LED lights, which is one of the effective methods for experienced buyers to evaluate suppliers.

4. LED package

The encapsulation of LED lamp beads is divided into resin encapsulation and silicone encapsulation. The price of the resin package is cheaper, because the heat dissipation performance is slightly worse, and the others are the same. Silicone encapsulation has good heat dissipation performance, so the price is slightly more expensive than resin encapsulation.

5. Service life

Although the lifespan of LEDs is 80,000 to 100,000 hours, because LEDs are constant current components, the constant current effects of LED lights produced by different manufacturers are different, and of course the lifespan is also different.

6. Color temperature

When purchasing, pay special attention to the color temperature below 3300K. The light color is reddish to give a warm feeling; there is a stable atmosphere and a warm feeling. It is commonly known as warm color temperature. The color temperature is in the middle of 3000-6000K, and people have no particularly obvious visual psychological effects under this hue, and there is a refreshing feeling; therefore, it is called "neutral" color temperature. The color temperature is more than 6000K, and the light color is bluish, giving people a cool feeling. It is generally called cold color temperature.

SMT quality control

1. Material inspection

Material inspection is IQC. The inspection of materials is a link to ensure the quality of production and is the basis for the smooth progress of SMT patch processing. Next, we will introduce you to the main points of inspection in detail.

1. Incoming inspection

Check whether the specifications, production, model, withstand voltage, appearance and size of electronic components and other materials are consistent with the BOM list provided by the customer to ensure that the materials meet customer requirements. There is also chip inspection. The size, pitch, package and pin of the chip, etc., all need to be QC tested.

2. Top tin inspection

Conduct tinning inspection on IC pins and plug-in component materials to check whether they are oxidized and the material's tin-eating condition.

3. PCB board inspection

The quality of the PCB board determines the quality of the finished PCB, otherwise there will be false welding, false welding and floating height. Therefore, it is necessary to check whether the PCB board is deformed, flying lines, scratches, circuit damage, and whether the board surface is flat.

4. PCB board eating tin inspection

The wettability affects the tin-eating rate of the PCB board, and a poor tin-eating rate will lead to insufficient solder joints.

5. Through hole inspection

The size of the through hole position is determined according to the size of the component. If it is too small or too large, the component cannot be plugged in or fall off.

2. Solder paste inspection

Solder paste source We use international brand Senju solder paste, which is supplied by specialized suppliers. The solder paste adopts the "first in, first out" standard of use in the use process, that is, the first to be purchased, the first to be used. The storage temperature of solder paste is generally between 0°C and 10°C, plus or minus 1°C. The solder paste needs to be thawed before it is used. Generally, it is about 4 hours at room temperature. It needs to be marked for use, and the rest needs to be recycled. However, the second time of recycling needs to be recycled to the supplier for processing to avoid environmental pollution. The solder paste needs to be stirred for 5 minutes with an automatic mixer before use to prevent air bubbles from entering the soldering process.

3. Steel mesh and scraper control

The size of the steel mesh is generally 37cm*47cm, and the tension is 50~60MP. Generally, a tension tester is used for tension testing. The storage temperature of the steel mesh is best controlled at 25 degree Celsius, and the edges of the steel mesh are rubber edges. If the temperature is too high, it will become brittle and cause damage to the steel mesh. The scraper is operated at a 45 degree angle, and the ordinary steel mesh scraper is scrapped after being used 20,000 times. Because the thickness of the steel mesh will become smaller, the tension of the steel mesh will be affected and the tin scraping will be incomplete.

Fourth, the placement machine adjustment and the first QC

Adjust the coordinates of the automatic placement machine according to the coordinate files such as the BOM, template and ECN file provided by the customer to ensure accurate measurement and high placement accuracy. This is the first QC inspection for placement. The quality inspector checks whether there are missing stickers, flying, placement direction and placement accuracy, etc. Mass production can only be carried out after confirmation.

5. Reflow soldering control and second QC

The temperature setting of reflow soldering requires different parameter settings according to the material of the PCB board, such as cardboard, 2-layer board, 4-layer board or ceramic board and so on. At the same time, the PCB board passing the furnace is to control the gap, direction and position of the board and so on. At this time, perform the second QC inspection test for the first reflow soldering to ensure that there is no melting of tin, whether the components are yellow, and there is no false soldering, and mass production after confirmation. This test requires an AOI test to check whether the monument is erected or not.

6. The third QC test

This inspection is a QA inspection by the Quality Department. The quality department needs to conduct random inspections on PCB finished products to ensure that they are packaged and shipped after they are qualified.