The PCB industry is overdue for modernization.
Familiarity breeds corner-cutting, with negative consequences.
Halides present post-reflow can cause severe corrosion.
Less-than-optimal preheat can lead to moisture-related defects.
Typically, when copper, organic solderable protectant (OSP) coated boards are left exposed after soldering, the copper oxidizes and darkens in color. It will quickly become unsolderable but does not corrode. If exposed to activated flux residues that have not deactivated after preheat and soldering, it is possible to see green verdigis on the copper surface. FIGURES 1 and 2 show a printed circuit board that has been soldered, and the exposed copper on the topside of the board around the pad shows the green deposit referred to as green verdigris.
Do aperture area ratio and aspect ratio play an equal role?
Miniaturization has been a central theme of this column for a long time. The enduring relevance of the topic speaks to the ever-moving goal posts when it comes to component sizes and printing dimensions. Today the industry is facing the reality of passive metric 0201s, which has prompted another look at the influence of stencil architecture on the printing process. The impact of introducing sub-150µm apertures means heterogeneous assemblies will include next-generation surface-mount devices that push area ratios below 0.5. To understand the bearing this will have on the print process, our team evaluated not only at area ratio – which has been the historic measure of printability – but also at the area ratio’s associated aspect ratios. The results were intriguing, to say the least.
By definition, the aspect ratio relates to the measurement of the shape of the aperture, and the area ratio corresponds to the aperture opening and side wall area. The formulas for both follow:
A Feb. 23 news item from the Associated Press cuts to the heart of the matter when it comes to reshoring of manufacturing and why skeptics (including this humble writer) abound over whether Foxconn and others truly intend to set up large manufacturing plants in the US: