IPC 4101 (Specification for Base Materials for Rigid and Multi-Layer Printed Circuit Boards) was released for publication in December, 1997. It was released as the replacement standard for MIL-S-13949. However, it contained a majority of the exact wording from the military standard. It maintained the “slash sheet” format appendix to the standard that specifies the resin and fiber system of different PCB laminates, along with testing parameters and properties. Initially there were 41 slash sheets, but as the industry opens up to “Lead Free” and “Green” processes, the slash sheets have increased to 66, the current revision.
As a contract manufacturer, say you receive a new circuit board part to assemble that is 6-layers with a high micro-via count, has blind and buried vias, and a lead free HASL finish. The circuit board laminate requirement is strictly Tg (Glass Transition Temperature) 170.
Bow and twist of printed circuit boards (PCB) tends to be the highest amount of falsely identified non conformances and the least understood. Perfectly flat rigid circuit boards as a norm, is a misconception held by many incoming inspectors. Understanding the reasons and causes for bow and twist can help resolve the issue at the board design stage.
As printed circuit board (PCB) designs get more demanding with advanced technology, involving complicated foot prints, and adding cost to components, incoming inspection of printed circuit boards need to have higher priority.
There was a time when “made in China” was synonymous with “cheap, poor, quality products”. Buyer beware was a common theme with outsourcing to Asian PCB manufacturers. So how did Epec approach this challenge and succeed? It was by managing quality through intense auditing, training, and qualification. Epec understood at a very early stage that first class quality product from Asian manufacturers would require constant presence, on-going training, and persistent auditing.
Cleanliness of bare circuit boards increases in importance with advances in PCB technology that continue to decrease conductor spacing. Inorganic contamination within printed circuit board fabrication can lead to electrochemical migration. Electrochemical migration is the dissolution and movement of metal ions in presence of electric potential, which results in the growth of dendritic structures between anode and cathode. These dendritic growths, which were minimal over periods of time, were not a concern of "yesterdays" bare boards.
When designing a circuit board one factor that must be considered is the solder mask and whether to go with matte finish mask or gloss finish mask. Usually, most designers don't specify which option and end up leaving the option to the PCB fabricator. This will likely lead to a gloss finishes which is more popular of the two.
When designing PCB's in a multi-up array, most designers choose v-score as the singulation method over traditional rout and breakaway tabs. The benefits gained range from effortless removal of parts from panel form, to realized cost savings with better utilization of panel area. When designing a circuit boards in array with v-score, there are two areas of concern - the angle of the cut, and the depth of the cut.
With rigid-flex printed circuit boards (PCB's), the transition from the rigid material to flex material (Transition Zone) can exhibit visual imperfections that, although acceptable, could affect the final part. These imperfections can consist of adhesive squeeze-out, protruding dielectric materials, crazing, or haloing. With the protruding dielectric materials (resin), the particles can have sharp glass-like qualities.
When a blow holes occur during the assembly process, as a result of the PCB card, the issue tends to be entrapped moisture or air. With moisture, any non-plated and non-masked areas on a bare circuit board, that expose internal laminate, can be suspect to absorbing moisture, both during board fabrication, and during improper storage. Examples of highly suspect areas are non-plated drilled holes and routed features.