1.What are "static strain" and "dynamic strain"?
Strain that changes slowly over time or remains essentially unchanged is called "static strain", while strain that changes rapidly is called "dynamic strain". However, there is no clear definition for the boundary between "static strain" and "dynamic strain".

2.Why aren't strain gauge resistance values set to 100Ω or 200Ω, which are easier to distinguish? Are there no strain gauges with such resistance values?

When strain gauges were designed in the United States in 1938, their resistance values were specified as standard 120Ω and 350Ω, and manufacturers around the world have adhered to this standard.

3.How to distinguish between uniaxial, biaxial and triaxial strain gauges?

A uniaxial strain gauge can only detect strain in one direction.

A biaxial strain gauge consists of two uniaxial strain gauges superimposed perpendicularly at 0 degrees and 90 degrees.

A triaxial strain gauge is composed of three uniaxial strain gauges superimposed at 0 degrees, 45 degrees and 90 degrees.

4.What material are the strain gauges commonly used in PCB testing made of?

The main component of general strain gauges for PCBs is copper-nickel alloy.

5. What are the application scenarios of PCB-specific strain gauges?

In the PCB manufacturing process, when the force direction is unknown or the force is complex, when measuring BGA devices, the values of principal strain, diagonal strain and triaxial strain in three directions can be calculated using triaxial strain gauges, and the strain rate can be obtained through processing. When testing V-CUT, single-axis strain gauges are often used for on-board components such as capacitors and resistors.

6.What is the relationship between strain gauges and the channels of a strain measuring instrument?

When measuring, a uniaxial strain gauge occupies one channel of the instrument, while a triaxial strain gauge occupies three channels.

7.What is the principle of a PCB strain measuring instrument?

A strain gauge is a sensing element made based on the strain effect, consisting of a sensitive grid and wires, and is used to measure strain. In use, it is firmly attached to the measuring point of a component. When the component is stressed, the measuring point undergoes strain, and the sensitive grid deforms accordingly, causing a change in its resistance. The strain signal is balanced through a Wheatstone bridge module, which can be converted into a corresponding voltage signal. After passing through the analog/digital circuit inside the tester, the voltage signal is converted into a digital signal, which is then captured and analyzed by dedicated software.

8.What is strain rate, and what value does it reflect?

Strain rate refers to the amount of strain change per unit time, reflecting the speed of strain change. The higher the strain rate, the lower the allowable strain change; the lower the strain rate, the higher the allowable strain.

9. What is the unit of strain?

Strain is a dimensionless unit, representing the ratio of the deformation amount to the original length, denoted by the mathematical symbol ε. That is, ε = ΔL/L. In daily written form, it is expressed as με, μm/m, and μe.

10.What are maximum principal strain, minimum principal strain and diagonal strain?

Maximum principal strain: The maximum and minimum orthogonal strains in a plane, which are perpendicular to each other and have zero tangential strain in their respective directions.

Diagonal strain: The directional strain that should be in a straight line or orthogonal to the 45° sensitive grid of the strain gauge, and its value is taken as the larger of the two.

11.What are the principles for selecting test points in daily PCB strain testing?

Based on the actual assembly, analyze the areas with large deformation, the areas with relatively high failure rates according to experience, the areas that are subject to repeated forces in the daily manufacturing process, and the components that are sensitive to strain as pointed out by the component suppliers.

12.What are the differences between three-wire and two-wire strain gauges?

The three-wire system eliminates the influence of wire resistance on strain testing. In the two-wire system, if the wire length is too long, it will affect the testing accuracy.

13.What is the appropriate sampling rate for PCB strain testing?

According to the standard, select 500-2000HZ based on different manufacturing processes. If it is too low, it may not show the true strain law. If it is too high, the data volume will be too large and it will also affect the processing speed of the later data.

14.How to conduct PCB strain testing?

First, select the PCBA measurement points: Which positions are the force-bearing points and which components are more sensitive to strain.

Second, develop a test plan: Develop a test plan based on the measurement points.

Three, prepare test samples: Prepare the corresponding PCBA templates and fixtures.

Four, strain gauge installation: Process the PCBA according to the selected test points and apply strain gauges.

Five, Measurement and Analysis: Conduct tests and report analysis.