Deformation of a board and package
Fig 5: Deformation of a board and package.

Calculating Trace Metal Fraction
The next step is to build the structural model for computation of deformation, strain, and stress. ANSYS SpaceClaim reads the ECAD geometry converting it into a 3D model of simplified layers, mapping the metal and dielectric properties onto the layers. That geometry is then opened in Mechanical where it is easily meshed due to the layer nature of the geometry. Each layer can have a combination of metal and dielectric properties. Some elements will be entirely metal, others entirely dielectric, and still others a mixture of metal and dielectric. The resulting mesh is a simpler swept hexahedron mesh, so you need only to adjust density to suit your purposes. A higher mesh density will produce a more accurate representation of the model and take more computational time. A lower mesh density takes less computational time and will be less accurate.

For greater insight into the accuracy of the model, you can also create a color-coded, source point cloud that takes advantage of the data map but is independent of the mesh, and assesses if a point is metal, dielectric, or something in between, enabling you to better understand thermal effects.

Calculating Thermal–Mechanical Stresses and Deformation
The resulting model with its mesh is the basis of a structural simulation with appropriate material properties taken into consideration. Its solution will quantify thermal stresses, strains, and deformation at any location on the board. By knowing these locations, you are able to determine whether some aspects of the model are at risk of failure, including attachment locations such as at solder balls. Icepak simulation also accounts for the cooling conditions of the board itself (for example, cooling fans). The engineer can also perform dynamic analysis to determine the modal frequencies and effects of random vibration on the board with thermal loading taken into account.

Stress of a board and package
Fig 6: Stress of a board and package.

This multiphysics simulation methodology gives engineers the ability — for the first time — to accurately determine the effects of thermal loading on a PCB within a timeframe that is relevant to a typical design cycle. One sample model with 2194 parts (55 board, 35 package and 2104 solder balls) and 3 million nodes and 3 million elements took less than four hours to set up and 18 minutes and 37 seconds to solve. You can now identify thermal loading issues, propose possible solutions and determine whether or not each of their proposed solutions solves the problem long before a prototype is produced. By understanding the effects of thermal loading on the structural integrity and reliability of the board in the early stages of the design process, engineers are empowered to design products with lower failure rates and reduced warranty costs while also reducing time to market and engineering expenses.


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