Printed Circuit Boards (PCB) provide mechanical support and the electrical interconnects needed for electronic and structural performance, and manufacturing survivability.
To accomplish these essential functions, PCBs must be constructed to address out-of-plane Coefficient of Thermal Expansion (CTEz), elastic modulus (Ez), or in-plane solder joint fatigue that lead to board failure.
The Designer-PCB Properties Relationship
CTEz measures the amount a component material expands when exposed to a change in temperature, and is influenced more by die and assembly processes than the designer or end user.
On the other hand, designers directly impact PCB properties based on how they approach four key elements that, individually or collectively, drive solder joint fatigue and board failure:
Glass: Glass styles range from high resin/low glass fiber volume to relatively low resin/high glass fiber volume. Most data sheet specifications are based on highest glass fiber style, providing no exposure to temperatures above the glass transition temperatures. Complex PCBs are typically constructed from lower glass content options, and designs must take this into consideration.
Copper: Copper weight is rolled out over a square foot to determine the thickness of the layer on the PCB. Most range from .5 mils to 4.11 mils. Since the copper layer is etched away to define the interconnects, the higher the copper weight, the more etching required resulting in higher resin concentrations – both of which are key considerations in the design, manufacturability and performance of the boards.
Laminate Resin: Copper-infused laminate resins vary in the type and number on each PCB, and contribute to thickness and manufacturing survivability. On multi-layer PCBs, each layer must be carefully evaluated both individually and in conjunction with all others. Laminate under-specification is common, resulting in failed stackups and other detrimental miscues.
Pre-preg Resin: Containing no copper, pre-preg resins are partially cured to fill in etched copper and glass voids, and are cured during the pressing process. Like laminates, pre-pregs are often under-specified, causing issues related to measurement, cleanliness and imprecise material control.
Sherlock Modeling and Simulation
Sherlock Automated Design Analysis™ Software allows for more accurate PCB modeling and evaluation to optimize the selection and stackup of glass, copper and resins.
With this one-of-a-kind software, designers have the tools they need to perform detailed FEA PCB modeling and to run multiple, complex simulations:
Stackup: The stackup tool allows for accurate selection of glass and fiber, which informs the overall material properties used during FEA analysis for the selected laminate.
High Fidelity PCBs: Sherlock can identify and mesh copper features within PCBs or substrates for insight into risks presented by warping, thermal issues, mechanical loads and the like.
PCB Meshing: Sherlock identifies homogeneous mechanical properties of the uniform (whole) model and those of each layer in a layered model. In uniform models, meshing demonstrated mechanical property variances only in-plane; in layered models, each element has properties computed based on location and layer.
Lead Modeling: Sherlock allows for the addition of through hole leads to select components and viewing virtually constructed PCBs in 3D, greatly increasing the FEA model complexity. FEA results are automatically post-processed to make predictions for lead vibration fatigue.
DfR Solutions’ Sherlock Automated Design Analysis™ Software gives designers the tools they need to achieve specified, appropriate CTEz and Ez for optimum PCB performance, solder joint reliability and successful boards.
You can try Sherlock for yourself – free! Request your no-obligation 3-week trial today by clicking the button below.