Solving solderability issues for printed circuit boards (PCBs) can be a real hassle. Nothing is more frustrating than having lined up all your materials for an assembly, only to start running the package through reflow and discover that the solder paste is wetting poorly to the pads. Immediately, the profile is checked to confirm proper parameters.
For customers and suppliers along the PCB manufacturing process, non-conformances will, unfortunately, happen from time to time. A non-conformance consists of receiving an order for printed circuit boards that do not meet your specifications or industry (IPC) standards. While dealing with these issues is obviously essential, the solution is sometimes not obvious and can put on-time delivery to your customer at risk. It is imperative that your circuit board supplier can deliver conforming product as soon as possible, which means having the procedures to get there.
With the introduction of ISO 9001:2015, which specifies requirements for quality management systems, the statement “quality management system documentation shall include a quality manual” no longer need apply. Many celebrated this as a reprieve from previously having to fully document their quality management system. However, eliminating the supplier quality manual altogether could be a dangerous takeaway on the new standard’s intention.
I can remember the first ‘incident’ of black pad, years ago, when Epec started to use the electroless nickel immersion gold (ENIG) process. We didn’t notice the issue at the time, as it is not evident on the bare board, but received the complaint from assembly as it was later identified on completed assemblies.
The V-score process is the addition of thin, double-sided cuts into printed circuit board (PCB) laminate for the purpose of assisting in the removal of individual parts from the array. The thin cuts which do not go all the way through the material, act as a perforation of the laminate so simple flexing of the laminate, or use of a cutting wheel, will aid in the removal of parts after the assembly process.
Among the multiple layers of a printed circuit board (PCB) lies the PCB silkscreen layer. The placement of the silkscreen markings, whether on the top or bottom layer, in conjunction with the features of the other layers, could affect the final legibility of the printed circuit board markings.
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 for meeting the Restriction of Hazardous Substances, or RoHS compliance, is strictly Glass Transition Temperature(Tg) 170.
Bow and twist of printed circuit boards (PCB) routinely rank among the highest levels of falsely identified non-conformance because it is perhaps the least understood. Envisioning a perfectly flat rigid circuit board as the standard is a fallacy believed by many incoming inspectors. Understanding the reasons and causes for PCB bow and twist can help resolve the issue at the board design stage.