2.4 ESD System Design Considerations

The following concepts are considered relative to an environment where the Contact package is the lone electronic device being attached to a disposable item. There is no PCB that can help to provide ESD protection; therefore, the Contact package alone must be considered.

ESD Protection Circuitry within the IC

ESD circuitry is built into the vast majority of integrated circuits. This circuitry provides some sort of clamping mechanism from the signal pins to ground or to the supply. Often there is also a clamping mechanism from the supply to ground. This circuitry is typically designed to achieve at least 2 kV HBM ESD protection but can often be designed for 4 kV or 8 kV HBM direct contact. This circuitry is designed to safely dissipate high-voltage discharge events and prevent damage to the device. The ESD circuitry is strategically placed on the die to shunt the high voltage directly to ground before it can reach and damage the more sensitive internal circuitry.

: The high-voltage value may actually be a large negative or positive voltage value. The ESD circuitry is designed to prevent damage against either polarity.

System Design Considerations

The goal of ESD protection is to always try to dissipate charge to ground before it can do any damage to the device. Additionally, preventing unwanted metal-to-metal contacts with the device pins will reduce possible ESD events. The pins of the device, when mounted to a disposable product, may ideally be protected from inadvertent contact. Contact may be from either an operator handling the device or machines, such as handlers and testers. When actual contact to the pins of the device is made, the contact discharge must be controlled.

Important: These recommendations are above and beyond the manufacturing recommendations already provided and must not be considered as an alternative method of protection.
All instances where the contacting of the pins may occur must be considered. This includes:
  • During initial manufacturing where the device may be tested or programmed prior to attaching to the disposable.
  • During testing or programming after the device is attached to the disposable.
  • During final usage after the disposable unit is connected to the host system.
Recessing the Mounted Device
By providing a small shroud around the outline of the device, a degree of protection can be provided from inadvertent contact. This may be done by hollowing out an area in the plastic casing that the device is mounted to, which allows the device to be slightly countersunk into the casing. Alternately, a small amount of plastic may be added around the device providing a small shroud around the device.
Controlled Pin Contact Order
The goal is to always dissipate the charge to ground; therefore, it logically makes sense that the ground pin is the first to get connected to the system. This can be done by using pogo pins of staggered lengths. Ideally, the ground signal would be the first to make contact, followed by the supply pin and, lastly, the signal pin. If only two pin lengths are used, the ground pin must be contacted first, followed by the supply and signal pin.

Product Packaging Considerations

ESD concerns carry over to the actual packaging and shipment of the disposable module with the device attached. Also, there may be several shipping stages. The first stage may consist of shipping many modules in a given package to the final packaging house, where they are broken out into single or small multipacks for final shipment to the user. Each of these stages needs to be considered. The following recommendations must be considered:

ESD Bags
An ideal option to protect the device on the module is to ship the entire module in an ESD dissipative bag. This may not be cost effective or may not work well with a given module.
Covering the Mounted Device
If the actual device is recessed, it may be feasible to place a small piece of plastic over the enclosure to protect the contact pins. This would protect the device through the shipping process with this plastic only being removed by the end consumer.
Conductive Packaging Material
To help in removing any charge build-up, conductive packaging material may be used to reduce the charge near the modules. This may be some type of ESD dissipative foam or some material that is treated to reduce charge build-up.
ESD Coatings and Sprays
An alternative to conductive packaging materials is to use more standard packaging materials that are treated with special ESD coatings and sprays. These coatings are used to reduce charge build-up.