Thermal Analysis Technology Used in R&D and Quality Control of Printed Circuit Boards (2)

TMA measurement (thermo-mechanical analysis)

The TMA can be used to measure the dimensional change of the PCB under zero load or deformation under a fixed load. METTLER TOLEDEO's TMA instrument has a resolution of 0.01 μm, which makes it impossible to detect changes that can be detected by the TMA technique under ordinary microscopes.

Figure 2 shows two TMA scans of the FR4 in the Z-direction: Initially, the FR4 sample is thermostatted at 30 °C for 10 minutes (ensuring temperature equilibrium is reached); in any case, the TMA curve for the first scan and subsequent scans Several times the TMA curve is always different, because the TMA curve of the first scan can often reflect the influence of stress on the manufacturing process of the FR4 plate or the length change caused by relaxation of internal stress during storage. , and volume relaxation due to gradual flattening of uneven areas. We usually use the second-scan TMA curve for quantitative calculations.

Fig. 2 TMA spectrum of FR4 (heating rate: 5K/min)

Figure 3 The expansion curve of FR4 panels in various directions (X, Y, Z) and shows the disaggregation of FR4 panels near 288°C.

Figure 4 The coefficient of linear expansion of the FR4 board in various directions (X, Y, Z).

Figures 3 and 4 show the coefficient of linear expansion of FR4 samples in three different directions:
dL 1
=————
Dt L0
The unit of linear expansion coefficient is 10-6°C-1.

The volume expansion coefficient is closely related to the exact angle between the three linearly measured coefficients of linear expansion.