What Is The Best Way To Mitigate CDM Damage and WHY ?

Current CDM control method centred around :-
1) Ionization methodology
2) Static dissipative material (Limitation in use due to the leakage issue during device testing)
 
The use of air ionizers in the mitigation and control of CDM or FICDM (Field Induced CDM) damage in factories has already been practiced for a long time. However, there are many pitfalls and shortcomings in the performance of an air ionizer that remains technically unresolved thus making the smooth implementation in the factories all over the world a challenging task.
 
One of the most critical pitfalls is their incapability to reduce the instant (in situ) peak voltage in the tribo-charging process. In reality, all commercial air ionizers failed as an effective CDM mitigation tool in delivering more effective solution to static field induction devices (CDM or FICDM) as compared to the RH Controlled Static Eliminator.  The promoters of air ionizers would certainly have a different opinion about this but the actual test data as disclosed in the later paragraphs supports this technical truth.
 
Surprisingly, it is discovered that water, one of the most natural resources abundant by nature, can provide advanced and exciting solution in the mitigation of CDM damage.
 
Humid air generated from water possesses its ability to help reducing the electrical resistances of the various components of a PCBA especially under elevated relative humidity conditions. Such findings were disclosed in the ESD Symposium papers in both 2012 (Singapore) and 2014 (Germany). 


Fig 1: Difference in the Working Mechanism of the Conventional Ioniser and the Novel RH Static Eliminator

More importantly, it is technically proven that humid air in an elevated humidity environment effectively cuts the magnitude of the tribo-charging voltages of ESD-sensitive devices. Such discovery reveals more insight in the understanding and the fight against the CDM damage in a real-life production process. Such findings was disclosed in the papers in the ESD Symposium Asia held in Korea in June 2015. It was learnt that humid air possesses the natural ability to provide surface lubrication to reduce friction during tribo-charging resulting in the reduction of static charge generation in a natural way.

A tribo-charging evaluation test was conducted to compare the magnitude of the tribo-charging voltage between a RH static eliminator and an air ionizer using a BGA chip (1” x 1”) as a test reference.  Such evaluation was done at various RH using an electrostatic voltmeter (TREK brand) with a one-stroke rubbing (tribo-charge) action and the results were tabulated in the table below:-

Relative Humidity (RH) : 42%

Table 1: CDM Voltage Comparison between the RH Static Eliminator and the Air Ioniser at different Relative Humidity (RH)

Test data obtained clearly show a startling difference in the magnitude of the tribo-charging voltages with air ionizer registered very much higher voltages from 300% to 1000% higher compared to that of RH static eliminator.  The test result is useful, valuable and extremely important for the ESD risk assessment because CDM damage currently poses the biggest threat to the ESD-sensitive devices manufacturers throughout the industry all over the world!

The findings conclude that RH controlled static eliminator is a much effective static charge mitigation tool with in-situ tribo-charging reduction capability many times better than that of an air ionizer.  It delivers a more effective solution to static field induction devices (CDM or FICDM) as compared to air ionizer.

It is also interesting to note that the use and application of such 100% natural environment friendly green static charge mitigation technique also eliminates the emission of health-hazard ozone (release during corona air ionisation) and further minimizes the risk of induced CDM damage resulted from the 5KV ionisation voltage as manifest in the conventional ionisation system.

Apart from the unique characteristics of humid air highlighted earlier, the application of such static charge mitigation technology is simple and easy-to-understand. It does not require demanding technical application knowledge like that of an ioniser to be effective. Its simple static charge mitigation system makes it easy to comply by all engineers and technicians in a typical mass production environment.

Unlike the highly volatile air ions generated by an ioniser, water vapour (humid air) at room temperature is intrinsically very stable by nature.  It is relatively easy and low cost to produce. It can be systematically transported or delivered in a controllable manner in any volume through tubing or piping to targeted spots or areas without much difficulty.

The portability and scalability nature of humid air (elevated humidity) are very unique and valuable asset in the mitigation against CDM or FICDM damage. It is technically superior and commercially attractive. Its design innovations and flexibility in large scale static charge mitigation applications are practically unlimited as illustrated in some of the air flow design configurations below:-

   

   

   

   

   
Fig 3: Various applications of the RH Static Eliminator

In contrast, such portability and scalability features are lacking in the current commercial ionization system. The lacking of such commercial benefit or advantage in the ionization system makes it less desirable as an advanced CDM control method for large scale implementation in the electronics manufacturing activities.

In conclusion, the use of RH controlled mitigation technology on CDM damage prevention is simpler to understand, cheaper to build (modular concept) and less complex to monitor comparing to ionization system making it an easy target to implement them on a large scale in an ESD-sensitive production all over the world painlessly irrespective of factory sizes and the complexity of the production system and processes.