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Software Analysis

Finite Element Analysis (FEA) is a numerical technique for finding solutions of boundary-value problems in structural analysis. FEA is commonly used for determining stresses and displacements in mechanical systems. FEA software is applied in various engineering environments and is generally adapted to popular CAD packages for use in diversified applications. The highly complex and versatile algorithms of this software can take several hours to solve a system including thousands of components, such as the probes in our in circuit test fixtures.

Here at Rematek, we have chosen to use an alternate method called Finite Difference Simulation (FDS). This numerical technique is perfectly adapted to our problems involving a thin plate and provides us with fast and precise results. The FDS analysis tool is directly integrated into our fixture design software called DrillCAD. This software, which has been continuously developed since 1994, has turned out to be the most sophisticated fixture design tool on the market. Its brand-new FDS functions now allow us to predict displacements, pressures and strains everywhere on the PCB very precisely during the fixture design stage.

Spring probe & pressure finger locations over board image

Our FDS tool not only lets us account for the force of the probes, the positioning of the fingers/stoppers and the thickness of the plate, but also the presence of components on top of and underneath the PCB. The 2D analysis software usually used in the fixturing industry considers the PCB to be a plate with uniform elasticity. Such software will compute that the maximum strain under a BGA is located at its centre. In practice, we know that the forces are concentrated on the outer edges of a BGA.

DrillCAD has been programmed according to a plate with non-uniform properties. It is thus possible for us to define the zones where the components add rigidity to the UUT. As described in the example in Image 3, a BGA will concentrate the forces and strains on its edges, reducing these same factors at its centre.

The following examples are showing the displacement and strain as a colored map over the UUT image, with and without the component effect. The red and magenta zones represent displacement greater than 0.005" or strain over |500|.

Displacement without components Displacement with components
Horizontal strain without components Horizontal strain with components
Vertical strain without components Vertical strain without components

Perfectly adapted to analysis of a thin plate such as a PCB, our FDS tool lets us obtain results with multiple iterations in a few minutes. Thus, we can quickly optimize the design of our fixtures to minimize the strain levels on the PCBs, without lengthening the delivery times of our projects. Once this work is completed, DrillCAD allows us to export all the necessary files to manufacture the fixture, such as the drilling files, the wiring files and the test files.

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