PCB copy board, classic PCB temperature curve system components

A classic PCB temperature curve system consists of the following components:

• data collection curve, which passes through the furnace and collects temperature information from the PCB.

Thermocouples, which attach to key components on the PCB, are then attached to the accompanying instrument.

Thermal insulation protects the instrument from heating the furnace.

• software programs that allow data gathered to be viewed in a format, rapidly determine welding results and / or find runaway trends prior to the runaway effects of final PCB products.

Thermocouple (Thermalcouples)

The most commonly used type of thermocouple in the electronics industry is the K thermocouple. Various techniques are applied to attach thermocouples to the components of the PCB. The methods used are determined by the type of PCB being processed, and the preferences of the user.

Thermocouple attachment

High temperature solder, which provides a strong connection to the PCB. This method is usually used for the purpose of sacrificing a specialized reference board for curves and inspection processes. It should be noted that the minimum amount of tin is guaranteed to avoid the effect of the curve.

Glue can be used to fix thermocouples on the PCB. The use of adhesives usually leads to the rigid physical connection of thermocouples to assemblies. Disadvantages include the possibility that the glue may fail in the heating process and leave a residue on the assembly when the curve is removed. Also, note that the minimum amount of glue should be used, because increasing the heat quality may affect the result of the temperature curve.

Capton (KaptON) or aluminum tape, it is the easiest to use, but the most unreliable fixation method. Using tape as a temperature curve often shows very uneven curves because the thermocouple points are raised from the contact surface during heating. Easy to use and leave no impact on the assembly of the residue, making cape or aluminium tape a popular way.

The pressure type thermocouple is clamped on the edge of the circuit board, and the thermocouple connection point is firmly contacted and fixed to the assembly which is doing the temperature curve by using the elastic force. The pressure probe is quick and easy to use and is not destructive to the PCB.

Thermocouple placement

Since the outer edge and angle of an assembly are more heated than the center, the larger heat element and smaller thermal mass element are used, so the placement of the four thermocouples is recommended. A thermocouple is placed on the edge or corner of the assembly, one on the small element, the other at the center of the plate, and the fourth on the larger element. In addition, thermocouples may be added to other parts of interest on the board, or to temperature shock or the most dangerous components of the temperature damage.

Read and estimate temperature curve data

Solder paste manufacturers generally have a recommended temperature profile for their solder paste formulations. The manufacturer's recommendation should be used to determine the optimum curve for a particular process and compare it with actual assembly results. Then, steps may be taken to change the machine settings to achieve the best results of the particular assembly (Figure three).

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

When do the temperature curves?

A temperature curve is especially useful when starting a new assembly. Furnace setting must be determined to optimize the process for high quality results. As a diagnostic tool, a curve instrument is invaluable in helping determine the rate of conformity and / or rework.

A temperature curve can be used to find inappropriate furnace settings, or to ensure that these settings are appropriate for assembly. Many companies or factories make temperature curves on standard reference boards, or use a machine's quality management curve every day. Some factories conduct temperature curves at the beginning of each shift to check the furnace operation and avoid potential problems before the problem occurs. These temperature curves can be used as a hard copy or by electronic format, and can be used as part of the ISO program, or to conduct statistical process on the performance of the whole machine time control (SPC STatistical process control) operation.

Used for temperature curve assembly, should be handled with care. The assembly may be degraded due to improper handling or repeated exposure to reflow temperature. The curve plates may be delaminated over time and the thermocouples may be loose, which should be expected and should be checked before each operation causes damage to the curve. The key is to ensure that the measurement equipment is able to achieve accurate results.

Classic PCB temperature curve and machine quality management curve

Although the most common type of temperature curve relates to the use of a running curve of instrument and thermocouples to monitor the PCB components of the temperature, the temperature curve is used to ensure the reflow oven with the best set continuous operation. A variety of built-in machine temperature curve instruments are available to provide routine measurements of key reflow furnace parameters, including air temperature, heat flow and conveyor belt speed. These instruments also provide the opportunity to quickly find any out of control trend before the out of control factors affect the quality of the final PCB assembly.