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We are using this SIM card holder in one of our designs. The SIM card can be inserted into the slot and fixed/released by gently pushing it in. So the contacts are protected from touching.

Would you still consider adding the common ESD protection that is suggested in almost every related application note? I don't see the point in this case, but maybe I am missing something.

EDIT: I forgot to mention the fact, that the case of the device has to be opened to insert the SIM card. This normally happens only once or a few times during device life time. So ESD test equipment wouldn't even come near the card holder.

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I would put them in. The ESD test involves putting the discharge probe near all the points that you can physically access and seeing if your device can handle the electric field generated. Looking at the sim-card holder design it appears that it would be impossible to direct the charge/field directly onto one of the internal pins given the large metal frame shielding them. Based on this it would initially appear that you don't really need any ESD protection.

However you need to consider the situation when a sim-card is partially inserted by a human charged up with ESD. If you have a look at a sim-card you will see that the bottom surface is basically a set of metal contacts, and it is entirely possible for charge to transfer from a person holding it onto an internal pin. Since this is not an unlikely scenario I would include the ESD protection.

In the end if you have doubts about EMI/ESD protection measures you should always include them on the board design. You can always cost out the design later by leaving them off after checking your design passes appropriate tests, but doing the reverse is much harder.

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  • \$\begingroup\$ True. I forgot to mention the fact, that the case of the device has to be opened to insert the SIM card. This normally happens only once or a few times during device life time. So ESD test equipment wouldn't even come near the card holder. However, your point about including it in the PCB design as a precaution is totally valid and I considered it anyway. The question was more about if to actually put the protection in place. \$\endgroup\$ – Rev1.0 Jul 2 '15 at 9:01
  • \$\begingroup\$ Since you mentioned it, I just tried out if it is possible to still touch the contact surface of the SIM card while pushing it so far in that it also touched the inner card holder contacts. There actually is a "critical millimeter" that is not obvious at first. So essentially the holder isn't touch proof after all. \$\endgroup\$ – Rev1.0 Jul 2 '15 at 9:16
  • \$\begingroup\$ That does make things a bit less clear cut. Presumably once the person has opened your device they can cause lots of havoc if they aren't using appropriate ESD protection anyway, so it does make the pin protection less useful. I would include it anyway, but you should probably think carefully about how the rest of the circuit is protected (maybe a plastic shield?). In my experience users do the craziest things and rarely follow instructions. \$\endgroup\$ – Jon Jul 2 '15 at 10:16
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Is your intention to pass ESD immunity tests, or make a product resilient to reality?

I don't see the distinction that just because the case might only be opened a few times in its life (to change SIM card) that your ESD-risk-per-human-touch-event is any lower, and that this therefore discounts the need for ESD protection. Keep in mind that creepage distances with ESD are long & usually difficult to fully itemise, and that you should 'expect the worst' when it comes to a combination of someone wearing isolated shoes on a low humidity day & be very 'poky' with their fingers.

OTOH, risk with or without ESD protection over the life of the product is of course a separate business decision, & that in turn has a bunch of factors that only you can estimate (the product's installed environment, climates (particularly humidity) your product is likely to encounter out in the field, the consequences of product failure (nuisance to catastrophe), the degree of expected litigiousness of your kind of customer, etc).

As @Jon pointed out, it's a LOT cheaper to design the protection in, and then test it with & without, and then have the luxury of being able to make an informed decision on broader risk analysis.

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  • \$\begingroup\$ Thanks, I tend to conclude that additional cost and increased layout space is worth it, even if the card holder will only be accessed a few times. \$\endgroup\$ – Rev1.0 Jul 2 '15 at 9:49

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