“PCB test coupons”refers to the test specimens or test boards attached to Printed Circuit Boards (PCBs).

I. Background and Definition

During the PCB manufacturing process, test coupons are small test structures designed at the edge or in the vacant area of the circuit board. They are fabricated simultaneously with the actual PCB circuits and are used to evaluate the quality and performance of the PCB manufacturing process. These structures contain various circuit features such as wires, vias, and pads, just like a small sample cut from the whole PCB for testing purposes.

II. Applications

1. Electrical Performance Testing
• They are used to measure the critical electrical parameters of PCBs, such as the resistance of the lines. For example, by designing  wires with specific lengths and widths on the test coupons, the resistance value per unit length can be accurately calculated, thus evaluating whether the conductive performance of the PCB's wiring layer meets the design requirements.
• Testing capacitance and inductance. For some PCBs with high -speed signal transmission, the values of capacitance and inductance can affect signal integrity. Test coupons can simulate the capacitance and inductance structures in actual circuits, facilitating measurement with professional testing equipment.
2. Reliability Testing
• Thermal stress testing is carried out. The PCBs with test coupons are placed in a high-temperature environment or an environment with cyclic temperature changes, and the performance changes of the circuits on the test coupons are observed. For example, it is checked whether the solder joints crack due to different coefficients of thermalexpansion.
• Humidity testing. In a high - humidity environment, PCBs may have problems such as moisture absorption and short-circuit.Test coupons can help evaluate the moisture-proof performance of PCBs, suchas observing the change of insulation resistance in a humid environment.
3. Solderability Testing
• The solderability of the pads is evaluated. The pads on the test coupons can simulate the actual soldering process. By applying       solder to the pads, the wetting condition, soldering strength and other indicators are observed to ensure that electronic components can be well-soldered to the PCB during the actual assembly process of electronic products.

III. Types

1. Electrical Performance Testing Coupon
• This type of test coupon mainly contains circuit structures for testing various electrical parameters. For example, there is a coupon specifically used for testing the characteristic impedance of transmission lines. It is usually a micro - strip or strip - line with a       specific length and width, and its characteristic impedance is measured with equipment such as a network analyzer to check whether it meets the design standards.
2. Mechanical Performance Testing Coupon
• It is used to evaluate the mechanical properties of PCBs, such as flexural strength. It may be a PCB specimen with a certain size and shape. During mechanical testing, a certain external force such as bending and stretching is applied to it, and the occurrence of mechanical damage phenomena such as fracture and delamination is observed to judge       the mechanical quality of the PCB.
3. Chemical Performance Testing Coupon

• It is mainly used to test the chemical resistance of PCBs. For example, the test coupons are soaked in a specific chemical solution  (such as an acidic or alkaline solution), and the corrosion on the surface is observed to evaluate the chemical stability of the PCB. This is very important for the quality control of PCBs of electronic products working in harsh chemical environments (such as chemical instruments).
  

I-TECH ELECTRONICS CO.,LTD regularly implements above test.