Measling in laminate substrates must not exceed what percentage of the spacing between noncommon conductors?

Measling in laminate substrates refers to the presence of faint white lines or patterns that can appear in the material due to various reasons, such as thermal stress or moisture absorption. The requirement that measling should not exceed 50% of the spacing between noncommon conductors is significant because it directly impacts the reliability and performance of the electrical assembly.

If the amount of measling surpasses this threshold, it could potentially lead to electrical insulation failure or signal integrity issues, as the integrity of the dielectric material between conductors is crucial for preventing unintended electrical paths or interference. Therefore, keeping measling to no more than 50% ensures that the substrate maintains its functional integrity and reliability.

In contrast, allowing measling levels of 75%, 100%, or even 25% would suggest higher tolerances that could compromise the performance of the electronic assembly. The specification for 50% ensures that while some degree of measling is accepted (acknowledging that it's often unavoidable), it must remain within a safe limit that will not compromise the overall assembly quality.