SMT reflow soldering process
From: Author:Mark Hardy Publish time:2021-09-09 10:31 Clicks:0
1) Requirements for the temperature recovery curve of solder paste:
The current reference temperature curve of solder paste MULTICORE and KESTER:
a. Preheating stage: 25°C to 130°C, the heating slope is less than 2.5°C/sec, and the time is 60~90 seconds.
b. Soaking stage: about 130℃ to 183℃, 1.5 minutes to 3 minutes. The middle part should be close to about 150±10℃. The maximum slope is less than 2.5°C/sec.
c. Reflow stage: 60~90 seconds above 183℃. The peak temperature is 210℃~220℃.
d. Cooling stage: The cooling slope is required to be 2~4℃/sec.
2) The company has a wide range of products, and the temperature setting should be based on the specific product and comprehensively consider the following factors:
a. Requirements for components:
If the temperature is too high, there will be potential damage to the components, especially the thermal devices and relay crystal oscillator devices. When the solder paste reflow requirements are met, the lower limit of temperature and time is taken.
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b. Layout and packaging of components:
For high component density and PLCC, BGA and other components with large heat absorption and poor thermal soaking performance, the preheating time and temperature should be taken as the upper limit.
c. PCB thickness and material:
The thicker the thickness, the longer the time required for soaking; for special materials, to meet their specific heating conditions, the main consideration is the highest temperature and duration that they can withstand.
d. Requirements for double panels:
For double-sided reflow soldering boards, first produce the side with smaller components; under the same conditions, produce the side with fewer components first, and the temperature setting of the reverse side should be different during production, generally 15°C to 25°C.
e. Production capacity requirements:
The running speed of the chain (mesh belt) is sometimes the bottleneck of the production line. In order to meet the production capacity, the chain speed can be increased, and the corresponding temperature setting needs to be increased (the wind speed can be unchanged), which should be confirmed by PROFILE.
f. Factors of equipment:
Consider the impact of different equipment. The heating method, the number and length of the heating zone, the exhaust gas discharge, the air flow rate, etc. should be confirmed by PROFILE.
g. Lower limit principle:
On the premise of meeting the welding requirements, in order to reduce the damage of temperature to the components and PCB, the temperature should be lowered.
h. When measuring temperature, substrates, devices with large heat absorption, and heat-sensitive devices should be equipped with test points to ensure the representativeness of PROFILE.
3) Modification control of process parameters:
1) The reflow soldering process parameters should be set and confirmed by the on-site process engineer.
2) When there are other abnormalities due to changes in environmental conditions or in order to solve soldering defects such as tin beads, monuments, etc., to modify the process parameters, it must be recorded in the "SMT Reflow Oven Procedure Change Record Sheet", and this modification must be made by Performed by on-site process engineer or confirmed by on-site process engineer.
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