The dynamic characteristics of SMA include dynamic changes in mechanical and physical properties such as temperature, stress, strain, and electromagnetic compatibility. With the miniaturization of SMA, these dynamic characteristics are becoming more and more sensitive to product assembly quality and performance. It is not only required for scientific design, but also has become indispensable in the design of products such as three-dimensional high-density SMA.
1. SMA thermal analysis design
Temperature is the main factor affecting the working reliability of electronic components. Temperature is directly related to a number of physical or chemical processes that usually degrade the reliability and performance of electronic components and electronic equipment. As far as semiconductor devices are concerned, they are extremely sensitive to high, low temperature and their changes. Usually high temperature will cause integration The characteristics of the circuit change. Many degradation and failure mechanisms of integrated circuits are related to temperature, such as corrosion and diffusion. High temperature will accelerate the action of these mechanisms, thereby reducing component reliability. In addition, the increase in temperature will also bring about a series of adverse effects such as increased leakage current of the integrated circuit, increased sensitivity to noise, drift of the operating point, unstable gain, and even thermal breakdown. Practice has proved that: every time the junction temperature of the integrated circuit increases ior, the failure rate will increase by about 1 times.
The internal components of the surface mount circuit module are arranged compactly, the assembly density is high, the temperature rise is prominent, and the heat dissipation is relatively difficult. In order to ensure high reliability, stable performance, and long life of surface mount circuit modules, it is necessary to conduct thermal stress analysis and research on the environmental stress and installation method of surface mount circuit modules and the thermal field distribution of surface mount circuit modules, and based on the analysis results, adopt Reasonable thermal design methods ensure that the surface mount circuit modules work reliably within the allowable temperature range.
The thermal field of surface mount circuit modules can be described by partial differential equations. Among the models of various thermal field problems and their numerical solutions, the finite element analysis method is particularly suitable for solving the problem of definite solutions of partial differential equations with complex boundaries and the vectorization of the solution process. Therefore, the finite element analysis method is used to analyze the surface Assemble circuit modules for thermal analysis. The finite element analysis method refers to the use of computers to solve differential equation problems in mathematical physics or engineering practice, mainly a systematic numerical calculation method for partial differential equation problems. The basic idea in a nutshell is “approximation by block” and “decomposition to meet requirements”. That is to say, the solution area is divided into a finite number of non-overlapping sub-regions, that is, “units”, and the approximate solution required by the equation will be approximated by the approximate functions in each unit, and finally from the overall point of view, considering the relevant factors, a A satisfactory solution that meets the conditions.
For thermal analysis of surface mount circuit modules, ANSYS can be used as an analysis tool. ANSYS is one of the most powerful general-purpose tool software used in finite element analysis and design. It is widely used in many industries such as aerospace, automobiles, and electronics. It is the first finite element software that has passed ISO 9001 quality certification. It can solve a variety of problems in different fields, in addition to powerful structural analysis functions (linear static analysis, nonlinear static analysis, linear dynamic analysis, nonlinear dynamic analysis), but also for other fields , Such as electric field, magnetic field, thermal field, flow field, etc., provide specialized algorithms and analysis functions. It also has perfect pre-processing, solving and post-processing functions. In the post-processing module, the powerful graphics function also makes the result analysis more vivid and direct.
A thermal analysis model of a three-dimensional component. The three-dimensional component is composed of 5 PCBs, which are 3 horizontally mounted and 2 vertically mounted PCBs, and integrated circuit chips are assembled on 3 horizontal PCBs.
In order to make the model solving process concise, the following assumptions are made:
(1) It is assumed that each printed circuit board is a tetragonal shape, and small chamfers, rounded corners and holes are ignored;
(2) The printed circuit board is flat, and there is no initial packaging on it except for the components;
(3) The circuit board is unified and balanced;
(4) The geometric form of the components in the printed circuit board analysis is not necessarily the actual product geometric form.
