Soldering Heat Resistance Test of Printed Circuit Board

Temperature is an important element of safety, reliability and performance in printed circuit boards (PCBs). High temperatures can cause malfunctions and permanent damage in a short time. Certain conditions can cause heating during the operation of a printed circuit board. For example, a component mounted on the board may generate excessive heat. An external factor, for example another component in a complex system such as an aerospace system or medical application, can generate excess heat. Heat may build up on the card due to insufficient ventilation. Or, the heat generated during PCB assembly, drilling and soldering can cause excessive thermal stress on components and cause boards to fail.

Whatever the cause, it is necessary to manage heat to ensure that printed circuit boards can withstand the high thermal stresses they will inevitably encounter. At this point, there is a need for effective PCB heat dissipation techniques and ways to prevent PCB temperature rise.

Monitoring the temperature of printed circuit boards is critical because high temperatures can change the board's structure, degrade its performance, or cause it to fail.

The main types of damage caused by excessive heat in a printed circuit board are:

• Loss of structural integrity: Excessive heat can damage the integrity of the board. The layers of this card are very sensitive to fluctuations in temperature and expand and contract when they get too hot or cold. Excessive heat can cause warping in the lengths, widths and thicknesses of the layers.
• Deterioration of circuit lines: Circuit lines expand and change shape when overheated. When this happens, circuits become susceptible to frequency shifts, distortions, and flat losses. Conductor impedances can also drift from the standard value. Millimeter wave circuits and microwave circuits, in particular, have small, delicate components that are easily damaged when they expand and deform at high temperatures.
• Incompatible material expansion rates: The harmful effects described above are compounded by the fact that different materials expand at different rates. A board has two basic layers: dielectric layers and conductive metal layers. Because these layers contain different materials, they expand differently in response to heat. Therefore, an overheating card can suffer more damage as the different types of layers are separated from each other.
• Oxidation: Oxidation of printed circuit board components is also a problem at high temperatures. If the dialectic material exposed on the cards does not have a protective laminate coating, it will not be protected against oxidation. In this case, the material may rust when exposed to high temperatures. This results in loss of transmission lines and a higher dispersion factor.

Before measuring temperature on printed circuit boards, it is important to identify the primary heat source on the board and locate the temperature sensors. Most of the heat generated on the PCB moves to the temperature sensor via ground pins connected to the bottom layer of the board. Because the pins are connected to the substrate, it has the lowest thermal resistance of any component of the board between the temperature sensor and the heat source.

PCB temperature measurement mainly includes three different steps:

• A ground plane is placed between the temperature sensors and the heat source.
• The ground pins of each temperature sensor are connected to the ground plane of the heat source.
• It is necessary to make sure that the temperature sensors and the heat source are close to each other on the PCB.

Printed circuit boards are generally defined as high temperature printed circuit boards if they can withstand the temperature limit of 150 degrees. Some high-temperature printed circuit boards can withstand even higher temperatures, but boards made from materials with less heat resistance can only operate safely at much lower temperatures.

Among the numerous test, measurement, analysis and evaluation studies given to the enterprises by our organization, there are also tests for the resistance of the printed circuit board to the soldering heat.