Avoid the infamous “Showstopper”
The IEC60601 standard isn’t simple to understand. Experienced engineers not trained in this standard may present sound designs but still have problems with certification. There are many grey areas when it comes to component certifications. The better you understand the standard, the more quickly (and cheaply) you can get the product certified. Here are ten pitfalls I have encountered as a Product Safety Engineer:
- Power Supplies – Leakage and Temperature
-Some Power Supply Units (PSU) are not fully certified for the type of medical device you may design. They may be acceptable for some applications, but not all. Low leakage current is critical and requires close examination of the power supply CB report.
-The critical components in the power supply will be monitored for maximum temperature in the final product. The original PSU tests are done in open air, and your product will require venting, fans, etc. that affect the temperatures.
- Bottom Vents
A chassis with bottom vents has very restrictive requirements to meet. Under certain conditions, the device may comply, but it’s best to avoid using bottom vents.
For details, see IEC/UL60602, Clause 11.3b, Table 25.
- Fuse Selection
Fuses have blow curves, so the current rating can be deceptive. It won’t instantly open with that exact current–it takes time. You want the fuse to open before other hazards occur, and this requires testing to ensure the fuse works, but isn’t too sensitive to routine surges.
- Laser Certificaton
If lasers are used, test reports and certifications will be closely scrutinized by the lab. The report must include testing of the failure modes for the laser. Many reports are incomplete and have skipped these tests! Refer to IEC60825-1 for details.
- Battery Packs
Standards for batteries, especially lithium-ion and other rechargables, have tightened considerably. You may select a certified battery cell, but if it is packaged as a multi cell battery, further testing is required. Example: You have selected a certified 1.5V NiMh cell and put 4 of these into a 6V package. Complete testing of the pack is required. Tests include failure modes and can be destructive. The testing can be time consuming and expensive. It’s best to find an existing certified battery pack, if possible.
Refer to the IEC62133 (supercedes UL1642) and IEC60086-4 standards.
- Circuit Board Thickness
For circuit boards, it’s easy to over-focus on creepage and clearance for insulating high energy or voltage circuits. Be aware that board thickness between layers is just as important. This is covered under Distance Through Insulation (DTI) in the standard.
- EMC Requirements
IEC 60601 requires rigorous testing for RF interference and susceptibility.
- Plastics Flammability
Selection of plastic for a housing requires consideration of flammability. Typically, you find a suitable plastic by checking a database, such as the UL certifications that have detailed listings and ratings. Make sure your design uses a thickness that is listed. If you use a 1mm thickness, and the minimum listed is 1.5mm, you fail!
- Plastics and EMC shielding
Metal coatings inside a plastic case may be necessary to meet EMC requirements. The combination of plastic and metal must be certified. This is to ensure the metal doesn’t break free of the plastic and cause problems with EMC and safety (e.g. shorts caused by metal flakes).
- Manuals for Users, Operators & Maintenance
This documentation, along with the product label are considered part of the product and therefore must be submitted with the product sample. If possible, avoid big production runs of these documents until final approval is received from the test lab.