It’s vital to meet FDA and ISO 13485 Standard quality and reliability requirements for medical ventilators and other medical equipment. But there’s still more that ventilator OEMs need to put into practice, specifically in the high reliability or Hi Rel area to further add to ISO 13485.
The term “Hi Rel” is most often associated with mil/aero PCB applications. But those same practices are synonymous with the high reliability expected for medical electronics, and again, in particular, to medical ventilators.
In both cases — mil/aero and medical equipment — added tolerances are built into processes and procedures as the foundation of high reliability PCBs. In other words, it’s going above and beyond the regular ones applied to commercial PCBs. Here, the savvy ventilator OEM plugs in additional reliability at PCB design, fabrication, and assembly. Various key steps at each stage get an extra five to 20 percent reliability factor.
Check out our SMT007 column to learn more about Hi Rel for medical equipment, including ventilators. In the meantime, here are some tips and hints to get you better acquainted with Hi Rel requirements.
- Solder paste printing is a major step for Hi Rel. Here’s where fully automated pick and place machines with advanced vision systems are critical to properly align fiducial marks.
- It’s important that either the printer efficiently measures the proper amount of dispensed solder paste on an empty pad or a standalone paste height inspection machine is used for that purpose, Fig. 1.
- Automated Optical Inspection or AOI assures all placements are proper, and there are no angles, skews, misplaced components, and/or polarity problems as it pertains to polarized components.
- A correct thermal profile is critical for meeting Hi Rel requirements.
- A Hi Rel PCB requires three to four iterations of the first article to assure a perfect thermal profile is perfectly created and verified.
- Conductive thermal compound helps to dissipate heat more efficiently. Also, soldering swages with heavy gauge wires to the pad and PCB, pre-tinning stranded wires when required assures sufficient solder.
Lastly, savvy Hi Rel PCB assembly houses working with medical equipment OEMs design solder stencils perfectly allowing perfect solder flow dispensing on the PCB pads. This assembly step increases reliability by an estimated five to 10 percent. Moreover, for acceptable quality levels (AQL), medical equipment and ventilator PCBs — just like mil/aero boards – must undergo 100 percent inspection to assure 100 percent reliability compared to the commercial standard of 0.65.