PCB Tech - PCB temperature curve system component composition

· Data collection curve meter, which passes through the middle of the furnace and collects temperature information from the PCB.

·Thermocouple, which is attached to the key components on the PCB, and then connected to the accompanying curve meter.

·Insulation protection, it protects the curve meter from being heated by the stove.

· Software program, which allows the collected data to be viewed in a format to quickly determine the welding results and/or find out-of-control trends before the out-of-control badly affects the final PCB product.

Three, thermocouple (Thermalcouples)

The most commonly used in the electronics industry is the K-type thermocouple. There are various techniques to attach thermocouples to PCB components. The method used depends on the type of PCB being processed and the user's preference.

Four, thermocouple attachment

high temperature solder, it provides a strong connection to the PCB. This method is usually used for operations where a dedicated reference board can be sacrificed for curve-making and process inspection. It should be noted to ensure the minimum amount of tin to avoid affecting the curve.

glue can be used to fix the thermocouple on the PCB. The use of glue usually results in a rigid physical connection of the thermocouple pair assembly. Disadvantages include the possibility that the glue may fail during heating, and leaving residue on the assembly when it is removed after the curve is drawn. Also, care should be taken to use the minimum amount of glue, because increasing the thermal mass may affect the results of the temperature profile.

Kapton (Kapton) or aluminum tape, it is the easiest to use, but the most unreliable fixing method. The use of tape for the temperature profile often shows a very jagged profile because the thermocouple connection point is lifted from the contact surface during heating. The ease of use and the absence of residues that affect assembly make Capetown or aluminum tape a popular method.

Pressure type thermocouple, clamped on the edge of the circuit board, use elastic force to firmly contact and fix the thermocouple connection point to the assembly where the temperature curve is being made. The pressure probe is quick and easy to use, and it is not destructive to the PCB.

5. Placement of thermocouple

Because the outer edges and corners of an assembly heat faster than the center, the larger thermal mass is heated up than the smaller thermal mass, so at least four thermocouple placement positions are recommended. One thermocouple is placed on the edge or corner of the assembly, one on the small component, another on the center of the board, and the fourth on the larger mass component. In addition, thermocouples can be added to other parts of interest on the board, or components that are most dangerous for temperature shock or temperature damage.

6. Read and evaluate temperature curve data

Solder paste manufacturers generally have specific recommended temperature profiles for their solder paste formulations. The manufacturer's recommendations should be used to determine the best curve for a particular process and compare with actual assembly results. It is then possible to take steps to change the machine settings to achieve the best results for the particular assembly (Figure 3).

For PCB assembly manufacturers, there are now new tools that make it easy to design target curves for specific combinations of solder paste and reflow ovens. Once designed, this target curve can be simply invoked by the machine operator at the opportunity of this special PCB assembly to automatically run on the reflow soldering furnace.

Seven, when to make the temperature curve

When starting a new assembly, it is particularly useful to make a temperature profile. The furnace settings must be determined to optimize the process for high-quality results. As a diagnostic tool, the curve meter is invaluable in helping to determine poor yields and/or high rework.

The temperature curve can be used to find inappropriate furnace settings, or to ensure that these settings are appropriate for the assembly. Many companies or factories make temperature curves on standard reference boards, or use machine quality management curve meters every day. Some factories make temperature profiles at the beginning of each shift to check the operation of the furnace and avoid potential problems before they occur. These temperature profiles can be stored as a hard copy or in an electronic format, and can be used as part of the ISO plan, or used to perform SPC statistical process control of machine performance over time.

The assembly used for the temperature profile should be handled carefully. The assembly may be degraded due to improper handling or repeated exposure to reflow temperatures. The curve board may delaminate over time, and the thermocouple may loosen attachment. This should be expected, and the curve device should be checked before each operation causes damage. The key is to ensure that the measurement equipment can get accurate results.

8. Classic PCB temperature curve and machine quality management curve

Although the most common type of temperature profile involves the use of an operating profiler and thermocouple to monitor the temperature of the PCB components, the temperature profile is also used to ensure that the reflow soldering furnace operates continuously with the best settings. There are various built-in machine temperature curve meters that provide daily inspection of key reflow oven parameters, including air temperature, heat flow, and conveyor belt speed. These instruments also provide an opportunity to quickly find any out-of-control trends before the out-of-control factors affect the quality of the final PCB assembly.