LEDDie bonding solder pasteNot only does it have a high thermal conductivity, low resistance and fast heat transfer, but it can also meet the requirementsLEDThe heat dissipation requirements of the chip, as well as the stable quality of the surface mount and high mechanical strength of the soldering, can effectively ensure the reliability of die bonding. The solder paste manufacturer briefly discusses the specific characteristic parameters:

Thermal conductivity:

The main alloy of die bonding solder pasteSnAgCuThe thermal conductivity of is approximately67W/m·KIt has low resistance and fast heat transfer, which can meet the requirementsLEDThe heat dissipation requirements for chips (generally, the thermal conductivity of silver glue is usually.1.5-25W/m·K"

Chip size:

The diameter of the solder paste powder is10-25μm(5-6#The powder can effectively meet the requirements5mil-75mil(0.127-1.91mmWelding of high-power chips within the range.

Crystal bonding process

Glue preparation - Glue removal and dispensing - mold bonding - eutectic welding. The dispensing cycle of the surface mount machine can reach240msThe placement cycle is150ms. The SMT speed is fast and the yield rate is high.

Welding performance:

It can withstand repeated dispensing for a long time, with full and bright solder joints and a porosity of less than5%The die bonding has good reliability and stable quality.

Thixotropy

Uniform particle size ultrafine tin powder and high thixotropic solder paste are adopted. They have good thixotropy, will not cause chip drift, and have low viscosity.10000-25000cpsThe size can be adjusted according to the dispensing speed.

Residue:

There is very little residue and it will be curedLEDThe base is placed in the incubator240After a few hours, the residue and the base metal will not discolor and will not affectLEDThe luminous effect.

Mechanical strength

The mechanical strength of the welding is higher than that of silver glue, and the weld points can withstand it10Newtonian thrust does not cause damage or flake off.

Welding method:

Reflow soldering or bench reflow soldering, where the temperature of the reflow oven is directly set at the eutectic temperature of the alloy for soldering, reduces the energy consumption for grain bonding.

Alloy selection:

Customers can choose the appropriate alloy according to their own patch requirements.SnAg3Cu0.5Lead-free solder paste compliesROHSInstruction requirementsSnSb10Its melting point is245-250°CIt meets the requirements of secondary reflow solderingLEDThe packaging requirement is that its thermal conductivity is close to that of the alloySnAgCu0.5.

Cost comparison

In meeting the requirement of high powerLEDAmong the bonding materials with heat conduction and dissipation requirements, the cost of surface mount solder paste is much lower than that of silver glue, silver paste andAu80Sn20Alloy, the surface mount process is more energy-efficient.

2,LEDCuring solder paste operation:

1Pay attention to the amount of solder paste manually or automatically. People don't feel well. In addition, excessive solder paste may spill onto the surface of the chip, causing a short circuit. Less solder paste will reduce the soldering area at the bottom of the chip and affect heat dissipation.

2Solder paste storage: The general storage temperature for solder paste is2-10℃Take it out of the refrigerator, heat it up and use it. The effect is very good. The usage time of solder paste each time should not exceed2-3Hours are appropriate.

3Solder paste baking time and temperature: Due toLEDThe chip is limited by temperature. During reflow soldering, the entire solder paste curing process generally does not exceed5Minutes, the highest temperature270Degree of8-10Seconds. If there is no reflow soldering and an oven is used, then the time needs to be mastered through multiple experiments.

Iii.ledSelection of die bonding solder paste.

Solder paste is a uniform mixture of solder powder (metal) and viscosity-stable flux, used to join two metal surfaces when heated. Solder paste has different properties due to the different components of solder powder, so different components have different uses; otherwise, unsatisfactory results will occur.

1Solder paste die bonding was the first to be proposed for useSnAgCuSolder paste crystal bonds, but experiments have found that it is usedSnAgCuAfter the solder paste crystal bonds and silicone encapsulation, they cannot withstand the subsequent lead-free solder paste reflow process.Leadfreereflowprocess),SnAgCuThe solder paste will degrade and become brittle, causing the chips and brackets to peel off. Due to poor contact, some voltages will rise, become unstable, and even short-circuit. Poor contact may also cause other problems, increasing thermal resistance andTjFailure. According to tests,SnCuSolder paste will not have this problem.

2Tin powder particle size: Currently in useLEDWhen surface mounting, the fluidity of the solder paste is highly required. The solder paste melts uniformly during this process. Therefore,LEDDie bonding solder paste is required to be used5#Or above pink mesh.

ledDie bonding solder paste has a high electrical conductivity and strong adhesion. Therefore, after the manufacturing process, it is difficult to determine whether the solder paste combines well with the chip through power and thrust tests. It is also necessary to observe the cross-section of the solder paste after the chip is pushed open, observe the coverage of the solder paste, and check if there are any holes inside the solder paste to confirm whether the process is normal. The solder paste process is recommended to use reflow soldering because reflow soldering can control the temperature curve and ensure uniform and stable temperature.