As electronic components become smaller, faster, and have lower operating voltages, their susceptibility to damage from Electrostatic Discharge (ESD) has increased dramatically. This condition is particularly evidenced by the absence of a chip carrier or substrate for advanced packaging component configurations including Flip-Chip, Chip-on-Board (COB) and wafer level chip scale packaging (CSP) manufacturing.

In the recent past when component operating voltages were much higher than those of present common use components, the packaging was more robust; a relatively high level of static charge could be tolerated and discharged. Some of this discharge could possibly be absorbed by the substrate, depending on the substrate material. Components were assembled on Printed Circuit Boards (PCBs) at a static grounded work station or by machines that were similarly grounded to a common electrical ground. The added level of component sensitivity to ESD requires air ionization in order to reduce or eliminate ESD charges during the movement of the assembly in the manufacturing process.

Technical Tip I: Install Air ionization in all locations where ESDS component handling or movement is difficult to control (Figure 7-1).

An ESD sensitive (ESDS) component placed on an insulating material connected to conductive patterns (constituting an induction coil) will generate and store a static charge when passed through an electrical (electromagnetic) field. This induced charge will then violently discharge when the assembly comes in close proximity to a ground potential. Identification and location of these charge fields is an absolute requirement for ESD protection in the assembly environment.  Simple apparatus such as unshielded lighting ballasts, inductors, motors, and solenoids are capable of creating these fields and should not be in the presence of ESDS components by less than 12 to 18 inches. Proper selection and placement of air ionization equipment will aid in the control or elimination of the ESD danger.

Technical Tip II: Identify all suspected or probable charge hazards, remove all unnecessary and suspect charge sources from the area and create “ESDS Safe Zones” for storage of WIP product at all levels of processing (Figure 7-2).

Environmental controls, another aspect of ESD control, have been a prime consideration in the electronics manufacturing industry since its beginning. The added requirement for establishing specific safeguards against ESD when humidity levels were below 30% was an absolute necessity in order to defeat the higher charge levels that would be generated. In the manufacturing of wafer level CSP, the “particle free” environment provided by clean rooms becomes a key element in producing components in quantity and with high levels of reliability. These wafers and insulating materials can become charged by air-borne contaminants and be damaged upon discharge. Air ionizers come in to play in the clean room on a large scale. Also, in the clean room, charge measurement and location of any ionization equipment becomes paramount.

Technical Tip III: Control the environment where ESDS components are stored, processed into kits, assembled onto PCBs, tested and packaged for shipment. These controls include removing all possible static generating objects, removing airborne particles (dust, etc.) and regulating the temperature and humidity in all of the above mentioned processing areas.