Detailed description of reflow soldering furnace temperature measurement method

Reflow soldering relies on the action of hot air flow on the solder joint, and the adhesive flux undergoes physical reactions under a certain high-temperature air flow to achieve SMD welding; The reason why it is called "reflow soldering" is because the gas circulates back and forth in the welding machine, generating high temperatures to achieve the welding purpose. So the standard for reflow soldering furnace temperature is very important, and it is necessary to test the reflow soldering furnace temperature standard. JEENOCE will share with you in detail the reflow soldering furnace temperature measurement method.

The temperature measurement of reflow soldering furnace is generally carried out using a temperature collector (i.e. temperature memory device) that can enter the furnace with the PCB board. K-type thermocouples (made of different materials according to the measurement temperature range and accuracy) are used for measurement, and the diameter of the thermocouple wire is appropriate to be 0.1-0.3mm. After the test, the data from the memory device is input into the PC special testing software for curve data analysis and processing, Finally, print out the temperature curve of the PCB component reflow soldering furnace.

1、 Selection of testing points for reflow soldering furnace temperature

The selection of testing points is generally at least three, which can represent the temperature changes on the PCB component (reflecting the temperature changes in high, medium, and low temperature parts of the PCB component); In general, the high temperature area is located at the center of the edge of the component perpendicular to the transmission direction of the PCB, while the low temperature area is located at the large component Haneda terminal near the center of the PCB (PLCC, QFP, etc.). In addition, there should be testing points on the surface of parts with poor heat resistance and specific customer requirements.

2、 Installation of thermocouple for reflow soldering furnace temperature testing

a. Thermocouples used for temperature sensing should ensure that no short circuiting occurs except for the test points during use and installation, otherwise the test accuracy cannot be guaranteed, and the test points should be as small as possible

b. When a thermocouple is connected to a memory device or other testing equipment, its performance should be consistent with the equipment requirements. The thermocouple converts temperature into electromotive force, so there is a directional requirement when connecting. (Currently, the thermocouple plugs we use have a positive and negative distinction)

3、 Pilot installation of reflow soldering furnace temperature measurement

The thermocouple should be reliably connected to the testing location, otherwise thermal resistance may occur. In addition, the materials in contact with the thermocouple and the materials used to fix the thermocouple should be small, as their thermal or endothermic effects will directly affect the authenticity of the thermocouple measurement values.

4、 Production of temperature measurement plate for reflow soldering furnace

4.1 Using a sample plate with the same production part number as the temperature measurement plate, when making the temperature measurement plate, necessary representative temperature measurement components should be retained in principle to ensure that the test measurement temperature is consistent with the actual production temperature.

If the temperature measurement plate and production part number cannot be consistent, after verification and approval by the engineer, the same type of temperature measurement plate can be used for measurement.

4.3 Temperature measurement points should be selected from the most representative area and components, such as the components with the maximum and minimum heat absorption. Priority should be given to component selection (such as Socket ->Motor ->Large BGA ->Small BGA ->QFP or SOP ->Standard Chip). In addition, a temperature measurement area between the two should also be selected.

4.4 Generally, there should be no less than 3 temperature measurement points on each board, and at least 4 should be selected for BGA or large ICs. Components should be selected based on the preferred principle of special representative components.

4.5 Location distribution: Adopting a full board diagonal or 4-corner-1 center point method, it can cover the distribution of the entire board position

4.6 The temperature measurement line should be fixed on the temperature measurement board with high-temperature resistant yellow tape or red adhesive.

5、 Test the reflow soldering furnace temperature curve

5.1 According to the temperature process limits set by the engineer, the furnace temperature testing technician pre sets the furnace temperatures for each zone based on different reflux furnace structures to meet the temperature process requirements

5.2 Insert the thermocouples on the temperature measurement board into the socket of the tester in sequence. Wear a protective cover, and be sure to insert the air line into the first socket.

After setting the furnace temperature, the temperature measurement board can only be used for testing after the green light of the reflux furnace lights up normally.

5.4 Carefully place the temperature measuring plate and tester onto the reflow soldering conveyor belt or chain, and turn on the power and data recording switch of the tester. The feeding method should be the same as the produced board.

After the 5.5 test is completed, remove the tester from the output end.

5.6 Read the temperature curve on the computer and check if the curve is within a reasonable process range. Otherwise, the technician needs to continue adjusting the temperature of each zone until a temperature curve that meets the process boundary is measured

6、 Collection of measured reflow soldering furnace temperature data

a. Open the computer KIC temperature measurement program as shown in the picture. And check if the solder paste process is OK

b. Input relevant information including furnace temperature, temperature zone, chain speed, testing channel, etc.

c. Connect the thermometer according to the prompts and start reading data.

d. Analyze the data according to the temperature curve requirements and print out the temperature curve that meets the regulations for archiving

e. Fill out the Temperature Curve Confirmation Form and have ME and IPQC confirm it is OK before posting it on the reflux furnace.

7、 Inspection after reflow soldering furnace

Check the welding situation of the substrate after passing through the furnace at this temperature setting, and confirm the rationality of this setting range and furnace temperature parameter setting based on this welding yield.

8、 Testing frequency of reflow soldering furnace temperature

The temperature of the reflow soldering furnace is tested by the technician once a day. If the wire is changed, it should be redone, and the correct temperature curve chart should be printed and filled out in the corresponding Temperature Curve Confirmation Form.

9、 Precautions for reflow soldering furnace temperature measurement

a. If the customer requests to measure the IC/QFP temperature, the thermocouple wire should be connected to the pins of the IC.

b. If the customer requests to measure the BGA temperature, a hole should be drilled on the BGA pad position on the front of the test board until the opposite side is reached. The thermocouple wire should be inserted from the opposite side of the test board into the BGA solder joint, and the entire BGA should be welded to the test board.

c. When measuring the temperature of hand soldered components, the thermocouple wire should be threaded through the solder hole from the front, extending a length of 1.5-2mm from the test plate to make contact with the tin wave.

d. Pay attention to safety during the testing process to prevent high-temperature burns.