Fixture Strain and Spring Force Deflection Limits on High Density Assemblies
Fixture spring force and deflection limits enforce maximum micro-strain thresholds to prevent latent BGA pad cratering and ceramic capacitor fracture during testing.
Multi-Layer HDI PCB Flexure
Mechanical Strain
Mechanical deformation properties of high-density interconnect boards quantify the amount of bending a substrate undergoes during assembly or operation. Managing multi-layer hdi pcb flexure prevents the rupture of small microvias and the shearing of fine-pitch solder balls. This measurement is important for thin boards used in mobile devices where space is limited and the board is part of the mechanical structure.
Microvia Reliability
The copper structures in high-density boards are smaller and more delicate than those in standard multilayer boards. Excessive multi-layer hdi pcb flexure puts a heavy load on the buried and blind vias which leads to fatigue and eventual open circuits. Boards with many layers are stiffer but also more prone to internal delamination if they are forced to bend too far.
Structural Limits
Testing the flexural strength involves applying a controlled force to the board and measuring the displacement until a failure occurs. Designers use the results to determine where to place stiffeners or how to design the enclosure to protect the multi-layer hdi pcb flexure from exceeding safe limits. The data helps in selecting the right resin system and glass weave to provide the necessary mechanical support for the dense circuitry.
Maintaining a flat profile during the solder reflow process is also essential to prevent permanent warping that would make the board unusable.