TEST METHOD OF PRINTED CIRCUIT BOARDS UNDER COMBINED MECHANICAL AND THERMAL ACTIONS Russian patent published in 2015 - IPC G01M7/00 

FIELD: instrumentation.

SUBSTANCE: invention can be used for reliability tests of the printed circuit boards (PCBs) and their components under combined mechanical and thermal actions. Tests are performed under two stages. At the first stage the load application points and point with maximum movement (deflection) are determined by calculation as per envelopes of the maximum movements of the results of testing of the preliminary developed FE model of the device with PCBs at all stages of standard operation, and load at each selected point is determined by equation: , where δ_j(x_i, y_i) is movement in j point under load applied to i point; P_i(x_j, y_j) is load applied to point i; G is coefficient of proportionality linking movement with load and cylindrical rigidity of PCB; is cylindrical rigidity of PCB (E is Young's modulus of the PCB material, h is PCB thickness, ν is Poisson number of PCB material), and loading of the selected points is performed sequentially by monitoring movement in other points, and, if necessary, movement is increased in further points determining maximum movement as per equation , where δ_max(x_j, y_j) if maximum movement in point j; $${\displaystyle \sum _{i=1}^N{\delta }_j\left(x_i,y_i\right)}$$ is summary movement in point j; N is number of points of load application (N ≥ 1); j is number of point with maximum movement; i is number of current point with movement; Δ is error of set movement, at that in the accessories for PCB installation the limit conditions are ensured similar to the conditions of PCB securing in the device, and stresses occurred in PCB not exceeding the permitted for PCB material and PCB installed components, and during acceptance tests the maximum movement is determined by equation , where η is safety factor of material strength in terms of movement. Using the acoustic emission (AE) method during deformation the damages in PCB design are checked. If PCB design has no damages then second stage is performed. Accessory with PCB is installed in the thermal furnace, and tests for thermal cycling is performed, at that number of thermal cycles and range of change of temperatures acting on PCB comply with the requirements of PCB acceptance tests. Using AE method during PCB thermal cycling the occurred damages are monitored, and upon thermal cycling completion PCB operation check is performed. Additional effect is obtained due to that upon the first stage completion the thermal cycling is performed with half of number of thermal cycles corresponding to the requirements of PCB acceptance tests, the accessory with PCB is removed from the thermal furnace, and PCB is re-arranged in the accessory rotating it to the indenters by opposite side, new deflection of PCB is made, and thermal cycling is repeated for half of cycles corresponding to the requirements of PCB acceptance tests.

EFFECT: development of the combined test method for mechanical and thermal; actions on PCBs at set load.

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