CHiC (components with high integrity characteristics) are components that have been deliberately over-designed so as to be fault free. So for example a normal (non-CHiC) X-type mains capacitor might have a 0.2mm dielectric thickness which already 99.99% reliable over the lifetime of the device even at maximum stress. For a CHiC component the manufacturer would double the dielectric thickness to 0.4mm, and do the same approach to all other critical parameters such as lead spacing, temperature margins and so on. This makes a component that is >99.9999% reliable. It's not that hard to do but as you can see it takes roughly twice the materials and size of a normal part, so it would be a waste to do this for every part.
Capacitors (Y2 type), special resistors, optocouplers are examples, but it can be done with anything as long as you have a good understanding of the physics and the "2 x normal" approach. These parameters can then be controlled in production in addition to sampling tests. Note that sampling tests are just to pick up mistakes (e.g. wrong material), it is not possible guarantee CHiC reliability based on tests alone. It has to be driven by an understanding of the physics involved, failure statistics, and then implementing margins that statistically guarantee >99.9999% reliability.
Note that this would not work with run of the mill electronic parts many of which have extremely low failure rates. For example, a typical unstressed SMD resistor would be >99.9999% reliable. The problem here is that the high reliability is unlikely to be guaranteed by design and production test, it's more likely to be a by-product of the commercial side. The manufacturers of these parts do not guarantee the super low failure rates and many even include such disclaimers against in high risk product in their datasheets (where failure of a part can lead to serious harm).
To understand more, consider for example a Y2 capacitor (specified as a CHiC), where the manufacturer moves production from one factory in country X to a new factory in country Y. Since the manufacturer is claiming CHiC characteristics, it is required to check the materials, dielectric thickness, lead spacing and all other ChiC related parameters in the new factory before releasing to market. If the manufacturer fails to do this, they can be held legally liable for any injury caused, including negligence and possible criminal charges. Of course, a medical device manufacturer that used that part in a device where the part failure led to harm would initially be held liable, but they can then transfer that liability on to the capacitor manufacturer.
In contrast, if SMD resistor manufacturer moves production from one factory to another, the new factory might experience teething problems associated with the local suppliers that drop the reliability rate to 99.98% in the first six months of operation, not enough for CHiC. That product could still be released to market, as the manufacturer never guaranteed the reliability to be CHiC levels. That manufacturer cannot be held liable if a failed resistor caused injury. In this case, medical device manufacturer would liable for the incident, without being able to transfer responsibility. They could also be found negligent, especially if the part manufacturer clearly stated not to use such parts in way that failure could lead to serious harm.
So, it is not just a matter of having a super low failure rate, but also knowing and controlling the parameters that ensure a super low failure rate. These parameters are the "characteristics" in the term "components with high integrity characteristics".
