Test method and process of reflow furnace temperature curve

1、 Purpose

This specification specifies the test cycle and test method of furnace temperature curve, so as to determine the best curve parameters through regular and correct furnace temperature curve test, ultimately ensure the best and stable quality of PCB assembly, improve production efficiency and product pass through rate, solve the test problems of engineering personnel, optimize production for enterprises and create more profits.

2、 Definition

1. Reflux curve

In the process of using solder paste, through the thermocouple and data collector fixed on the PCB surface, the visual data set of PCB time and temperature in the reflow furnace is tested. According to the curve recommended by the solder paste supplier, the best set of furnace temperature setting parameters for different products are obtained by appropriately adjusting the temperature setting and the speed of the transmission chain.

2. Curing curve

In the glue dispensing or printing process, the visual data set of PCB time and temperature in the curing furnace is tested through the thermocouple and data collector fixed on the PCB surface. According to the curve recommended by the solder paste supplier, the best set of furnace temperature setting parameters for different products are obtained by appropriately adjusting the temperature setting and the speed of the transmission chain.

3. Basic products

It refers to the products as the basic type in a product series, on which other products of the series can change the mounting state or make a small number of revision to the printed board. Generally, the drawing number of the printed board with the same function in a product series is only distinguished in the version number.

4. Derivative products refer to those generated due to the change of design mounting status or a small amount of revision of printed boards on the original basis. The number of chip devices changed is not more than 50, and the overall dimension is not greater than □ 20mm × 20mm IC devices (excluding BGA, CSP and other specially packaged devices) are adjusted.

5. Brand new products

It refers to that the number of chip devices generated when the product company newly develops, changes the design mounting state or modifies the printed board on the original basis exceeds 50, or the overall dimension is greater than □ 20mm × The number of 20mm IC devices is adjusted. All products with BGA, CSP and other special packaging devices added or reduced in the state change are regarded as new products.

6. Test template

It refers to the actual board used to test the furnace temperature. Strictly speaking, the board must be pasted with components basically consistent with the production state used to test

3、 Selection of temperature test points for reflow soldering furnace

The selection of test points is generally at least three parts, representing the test points of temperature change on PCB assembly (which can reflect the temperature change of high, medium and low temperature parts on PCB assembly); Generally, the high temperature part is at the center of the edge of the component perpendicular to the transmission direction of the PCB, and the low temperature part is at the half field terminal of the large component near the center of the PCB (PLCC. QFP, etc.). In addition, there should be test points on the surface of parts with poor heat resistance and the specific requirements of customers.

4、 Manufacturing method of product temperature measuring point

The thermocouple shall be reliably connected with the test position, otherwise thermal resistance will be generated. In addition, the materials in contact with the thermocouple and the materials for fixing the thermocouple shall be small, because its heat or endothermic effect will directly affect the authenticity of the measured value of the thermocouple.

5、 Manufacturing method of temperature measuring plate

1. The sample plate with the same production material number shall be used as the temperature measuring plate. When making the temperature measuring plate, in principle, necessary representative temperature measuring components shall be retained to ensure that the test and measurement temperature is consistent with the actual production temperature.

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

3. The most representative area and components should be selected for the temperature measurement point, such as the components with maximum and minimum heat absorption. The priority of parts 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. Generally, there shall be no less than 3 temperature measuring points on each board, and at least 4 for BGA or large IC. Components shall be selected based on the principle of special representative components.

5. Position distribution: adopt full board diagonal mode or 4 corners and 1 center point mode, which can cover the position distribution of the whole board

6. The temperature measuring line shall be fixed on the temperature measuring plate with high temperature resistant yellow tape or red glue.

6、 Test reflow furnace temperature curve

1. According to the temperature process limit set by the engineer, the furnace temperature test technician preset the furnace temperature of each zone based on different reflux furnace structures to meet the temperature process requirements

2. Insert the thermocouples on the temperature measuring board into the socket of the tester in turn Put on the protective sleeve and pay attention that the air cable must be inserted into the first socket.

3. After the furnace temperature is set and the green light of the reflux furnace is normally on, the temperature measurement board can be used for testing.

4. Carefully place the temperature measuring board and tester on the conveyor belt or chain of reflow welding, and turn on the power supply and data recording switch of the tester. The way of entering the Board shall be the same as that of the produced board.

5. After the test, take out the tester at the outlet end.

6. Read out the temperature curve at the computer end and check whether the curve is within the reasonable process range. Otherwise, the technician needs to continue debugging the temperature of each zone until the temperature curve meeting the process limit is measured

7、 Collect the measured reflow furnace temperature data

1. Open the computer temperature measurement software. And check whether the solder paste manufacturing process is OK

2. Input relevant information, including furnace temperature, temperature zone, chain speed, test channel, etc.

3. Connect the thermometer according to the prompt and start reading the data.

4. Analyze the data according to the requirements of temperature curve, and print the temperature curve that meets the requirements for archiving

5. Fill in the temperature curve confirmation form and post it on the reflux furnace after it is confirmed by me and ipqc.

8、 Post reflow inspection

Check the welding condition of the base plate after passing the furnace under this temperature setting, and confirm the rationality of this setting range and furnace temperature parameter setting according to the welding yield.

Solutions to the problems caused by the change of furnace temperature parameters

1. False soldering: the solder paste is not or not fully welded with the device pins, which can be solved by increasing the reflow temperature or time.

2. Continuous soldering: usually reduce the temperature or time of reflow zone to improve the phenomenon of continuous tin.

3. Solder beads: due to the high temperature or short elapsed time in the preheating area, the moisture and solvent in the solder paste are not fully volatilized, and the solder beads are splashed in the reflux area. Therefore, reducing the temperature or time in the preheating area and reducing the rising slope can be solved.

4. Solder joint is not bright: it is not bright caused by the solder joint is not full. It can reduce the temperature of reflux zone or speed up the chain speed.

The non brightness caused by insufficient melting of solder paste can be solved by increasing the temperature of reflux area or slowing down the chain speed.

5. The main defect of glue solution is insufficient bonding strength (parts are easy to fall during wave soldering or transfer). The solution is to increase the temperature or slow down the transmission speed due to insufficient curing temperature and time. If it is caused by glue aging due to excessive curing temperature or long time, reduce the temperature or speed up the transmission speed at this time.

9、 Furnace temperature test management

The reflow furnace temperature shall be tested once a day by the technician. If the line is changed, it shall be done again, the correct temperature curve shall be printed, and the corresponding temperature curve confirmation form shall be filled in.

1. Furnace temperature test cycle: in principle, the Engineer shall test once a month according to the products produced in the current month, record the test results in the "furnace temperature parameter setting registration form", and print and archive the furnace temperature curve.

2. In principle, the new products must pass the furnace temperature test to determine the accurate furnace temperature setting parameters. However, for the new products with a batch of less than 100 sets, the engineers can adjust themselves according to the original similar products and the welding effect of the observed objects.

3. New products shall receive new test samples during furnace temperature test. Derived products can use the test samples of the original basic products for furnace temperature test, so as to set corresponding and accurate furnace temperature parameters for different products and states.

10、 Precautions for temperature measurement of reflow furnace

1. If the customer requires to measure the IC / QFP temperature, the thermocouple wire shall be connected to the IC pin.

2. If the customer requires to measure the BGA temperature, drill a hole on the BGA pad on the front of the test board until the reverse side, insert the thermocouple wire from the reverse side of the test board into the welding joint of BGA, and weld the whole BGA on the test board at the same time.

3. If it is necessary to measure the temperature of hand welded elements, the thermocouple wire shall pass through the welding hole from the front and extend out of the test plate for 1.5-2mm in order to contact the tin wave.

4. Pay attention to safety during the test to prevent high temperature scald.