One of the more rigorous tests that can be performed on a printed circuit board is a destructive physical analysis (DPA). Despite the name, the initial steps of a DPA are non-destructive and involve a thorough inspection of the board as received, with emphasis on studying the process quality of things like plated through-holes, solder mask, and conductor trace spacing. This inspection is usually accomplished with a combination of optical microscopy and x-ray imaging. Next, the board will be cross-sectioned in several different areas in order to gather data about the uniformity of the PCB manufacturing process. Measurements are taken of dielectrics and conductors to ensure the boards are meeting or exceeding minimum specifications; the general construction of the board is also evaluated. Special attention is given to the vias and through-holes on the board so that any stress cracking or improper plating can be identified. If the board has been populated with components, cross-sectioning may also be employed to examine the integrity of solder joints between the board and its devices.
A populated board may also be the subject of an audit to ensure compliance with the Restriction on Hazardous Substances (RoHS) directive. RoHS requires that consumer electronics be free of a handful of elements and compounds that constitute significant ecological hazards; one of the most common printed circuit board tests, a RoHS audit, is a service that determines whether a given PCB meets these standards. A RoHS audit can be a standalone analysis, or performed as part of a DPA; the primary tools necessary for the audit are elemental analysis tools, like energy dispersive spectroscopy or x-ray fluorescence, and can analyze either whole boards or cross-sections thereof.
With the increased complexity of printed circuit boards, there is an increasing need for external test services due to the increasingly extensive nature of the analysis. It is often necessary to subcontract DPAs or RoHS audits to outside firms, with the experience and capability necessary to perform effective, insightful analysis.