Utilizing the strain effect of metal conductors, the strain of the PCBA is quantified by the change in resistance value of the strain gauge (strain rosette) attached to the PCBA as it undergoes mechanical deformation along with the deformation of the PCBA. Thus, by comparing this quantified strain with the limit strain, the risk of component or component solder joint rupture due to the deformation of the PCBA can be judged, providing a direction for improvement measures in the PCBA manufacturing process.
The strain testing system detects the voltage change caused by the change in resistance value of the strain gauge through the Wheatstone bridge. Then, through the program in the strain testing software, the voltage change is converted into strain.
The strain rosette is a strain gauge containing three independent sensitive grids. They are stacked on top of each other at a common point and are used to measure the strain along their respective axes at a common point.
Strain is defined as (change in length)/(original length) and is a dimensionless physical quantity. In PCBA strain testing, since the strain value is extremely small, it is usually described in microstrain (με), which is defined as 106*(change in length)/(original length).
In PCBA strain testing, the strain state of the PCBA is a plane strain state. The strain test analysis system can calculate the principal strain and strain rate during the PCBA manufacturing process by measuring the real-time strain values in three directions of the strain rosette to determine whether the product strain in the manufacturing process exceeds the standard.
Steps exceeding the strain limit are considered as excessive strain and are confirmed for corrective measures to be taken. The strain limit can come from customers, component suppliers, or well-known practices within the enterprise/industry (derived from IPC_JEDEC-9704A).
Among them, the principal strain is the maximum and minimum orthogonal strains in a plane. They are perpendicular to each other and the shear strain in the direction where they are located is zero. In PCBA strain testing, the principal strain is usually measured and calculated as the critical measurement criterion; the strain rate represents the speed of strain change per unit time and is used to measure the risk of component damage.
Post time: Oct-18-2024
