By Dimensional Stability in Electronics Boards
The electrical circuitry in a modern electronics board is intricate and compact. The design must be accurate and fit within the confines of its enclosure. It must communicate with the outside world through a variety of connectors mounted on its surfaces. It must perform efficiently and be stable to withstand vibration and thermal cycles. Dimensional stability is a complex issue that requires a precise understanding of PCB fabrication processes and material properties.
The dimensional stability of a circuit board depends on the tolerances the fabricator sets and the material’s normal coefficient of thermal expansion. It also depends on the specific etching process, copper electroplating, pressures, temperatures and chemistry. These factors create a matrix of small changes that add up to larger overall panel shrinkage or expansion.
A circuit board’s dimensional stability can be improved by designing a balanced stack-up that minimizes flexing and twisting. The use of stiffeners helps lock a electronics board into a planar flatness that enhances surface mount component assembly and acts as a heat spreader. Incorporating a slab of metal into the board’s base or center, called a ground plane, can improve dimensional stability and prevent bow or twist by acting as a stiffer substrate.
How to Ensure Dimensional Stability in Electronics Boards
Another important factor is the selection of a dielectric material. The choice of a material with the appropriate loss tangent and dielectric constant is critical for high-speed digital design. Choosing an unnecessarily low-loss material can increase the cost of the circuit board without improving performance.
In addition, proper spacing between signal traces and the board edges is essential to reduce crosstalk. Incorrect signal propagation due to the proximity of signals to each other can lead to errors in logic operation. This is commonly known as insertion loss, and can be reduced by proper routing design and spacing.
PCBs with a high insertion loss can have erroneous behavior and fail in operation, often without an obvious cause. Identifying this issue early on in the design process is crucial to avoid costly rework and production delays.
The final step in the PCB manufacturing process is soldering. For a high-quality result, the metallization of the copper must be complete. Achieving a high-quality metallization is dependent on the thickness of the copper layer, as well as the quality and consistency of the copper plating process. Incorrect or inconsistent plating can lead to weak points in the metallization that can result in short circuits, bad connections, or even an entire failure of the circuit board.
In order to ensure dimensional stability and the highest possible quality, PCBs must be manufactured according to a strict set of standards. The PCB assembly drawings should clearly indicate the polarity of the components, their positioning relative to the center line and the via dimensions. Inconsistent or inaccurate assembly drawings can cause a wide range of problems, including component mismatch and signal integrity issues. Inconsistent or inaccurate drilling and hole size specifications can also result in a finished product that fails to meet the required specifications.