ESD News

What are the ESD Classifications? A Look at the Machine Model

by David K. on November 14, 2011

Over the last two weeks we have gone over the human body and charge device models of ESD classification. This week is the last in our three part series, and we are going over the machine model.

The machine model is the most straightforward of the three ESD classifications. It shows how sensitive a device is to other charged devices in the area. For instance, if there are charged wires around your work station and they touch your ESD sensitive device, machine model classification tells you how much voltage can discharge from the wire to the item before it is affected.

To the left are the classification levels for the machine model. When testing products to place them in a specific class you typically charge a probe to the voltage range you want to test, then touch it to an ESD sensitive part of the device. Then test the item to see if this discharge caused damage.

This marks the end of our ESD classification series! If you need any more information on the ESD classification systems then check out www.esda.org. They have documents on the classification models, as well as a glossary of terms and a lot of other information. Starting next Monday we are going to shift gears and start to talk about electrical testing equipment, such as the new Monroe Electronics meters we will soon be adding to our site. Also make sure to check out the first two parts of our ESD classification series, linked below.

Read Part 1 of “What are the ESD Classifications? Human Body Model”

Read Part 2 of “What are the ESD Classifications? Charge Device Model”

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What are the ESD Classifications? A Look at the Human Body Model

by David K. on October 31, 2011

When working with ESD sensitive products you need to know exactly what protection is needed. To help let workers know how sensitive certain devices are there are several classifications that are used. The three ESD classifications are the human body model (HBM), charge device model (CDM) and the machine model (MM). Each has its own standards for different situations in ESD-safe rooms and products. In this article we will be looking at the human body model classification.

The human body model is the most common classification system for ESD-safe products. When preparing a room with HBM concerns you are trying to stop static buildup on humans from discharging to a conductor. The various classifications for this model tell the user what level of voltage will damage the parts being made.

To the right is a chart of the various classifications for the human body model. The lowest class is Class 0 which requires very stringent regulation. In order to meet this classification you need to make sure that you have the best systems in place possible for dissipating charge on human operators.

HBM classification deals with direct, short bursts of current, so products are typically put into various classes through a rather simple process. The tester will normally hook up the device to a positive and negative lead and given a pulse of a specific voltage level. The voltage of the pulse is increased until the product is damaged and that level designates the class of the project.

If you want to make sure your work area is ESD-safe there are a number of products that you can use. Surface resistivity meters allow you to test any ESD-safe mats or flooring that you have to make sure they are as conductive as they should be. Having conductive, dissipative, or anti-static mats and flooring can help reduce the amount of charge generated from the operator moving around. To directly check the operator you can use workstation monitors. These can check that the workstation, worker, and wrist strap are properly grounded to protect your products.

If you have any further questions about the human body model classification leave a comment below or check out Electrostatic Discharge Association’s website.

Make sure to check back in next Monday, November 7 for another blog post on the charge device model ESD classification system!

Read Part 3 of “What are the ESD Classifications? Machine Model”

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Lower CDM Ratings in Large Printed Circuit Boards?

by admin on September 23, 2010

As presented in this month’s edition of IN Compliance Magazine, “Decreased CDM Ratings for ESD-Sensitive Devices in Printed Circuit Boards” describes the increased vulnerability of electronic devices when placed into printed circuit boards (PCBs). Authored by Roger Peirce of Simco and Jim Colnar and John Trotman of General Dynamics, this article puts a new spin on the ESD world.

HBM (human body model) ratings are typically used more than CDM (charged device model) ratings because they are easier to acquire from manufacturers. However, a device’s CDM rating may be more relevant in situations where a device can become charged by an adjacent insulator. But because CDM ratings are difficult to determine from HBM ratings, the article’s authors sought out to find a correlation between CDM and PCB size.

From exploratory tests discussed within the article, the results show that an electronic device’s CDM rating is drastically lowered when mounted into a larger PCB. The original device in question tested at 3500 volts. When placed into a 4 x 4” PCB, the device tested at 2200 volts. It was then placed into larger and larger sizes of PCBs. When inserted into the largest PCB, at 12 x 12”, the lowest voltage was found at 900 volts (see Table 1).

Although this information is relatively new and experimental, it does bring awareness to the vulnerability of electronic components in printed circuit boards. It also raises the question of whether or not a component’s CDM rating can be found using the multiplying factors from Table 1. With more testing, this information could potentially be used as a future standard for calculating such CDM ratings. Stay tuned!

Find component testers, PCB carriers, and PCB repair parts at All-Spec Industries.

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Basic Parts of a Weller Zero-Smog Fume Extractor

by admin on January 29, 2010

We recently added Weller’s line of Zero-Smog fume extractors . Fume extractors are an integral part of any workplace environment where hazardous fumes and/or smoke are present. Exposure to the fumes can cause nosebleeds, asthma, sore throat and possibly even long term health problems.

In basic form, all Weller fume extractors have three parts, a collection point, an airflow source and of course, a filter system.

1. The collection point is just that, a place where the fumes enter the fume extraction system. There are two different types of collection points: volume extraction and tip extraction. The common goal for both types of fume extractors is to remove the fumes as close to the source as possible.

Tip Extraction – Used for hand soldering or any small work area…the fumes typically travel through a small tube mounted on the iron.

Volume Extraction – This type of extraction is for larger areas and is usually set up with a nozzle positioned as close to the source of the fumes.

2. The airflow source is simply how the fumes get from the source to the filter. Understandably, the size and type of vacuum pump used depend on the size and type of extraction system.

According the Weller’s Zero-Smog site, volume fume extractors require a high airflow rate but a lower vacuum (generally 2,800 Pa maximum). On the other hand, tip fume extractors use a lower airflow but a higher vacuum (up to 12,000 Pa for efficient fume extraction)

3. The star of the show is of course the filter system. Weller units employ three filters to get the job done. The first is a dust filter to remove the largest particles. The second filter is a microfilter designed to remove nearly all the smaller particles. Lastly, the gas filter uses activated carbon and chemisorbant to clean the airflow.

All of Weller’s fume extractors are ESD-safe and available with a variety of ports, filters, arms, hoses and nozzles.

Having trouble trying to decide which fume extractor to purchase? Use Weller’s fume extractor selection guide to assist you in figuring on what system fits your application.

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Creating an ESD-Safe Workstation

by admin on February 3, 2009

If you’re working in an environment where ESD (electrostatic discharge) is something you absolutely must avoid, it’s very important to have a proper ESD Safe workstation. Knowing exactly what ESD is and having the right tools can make all the difference in protecting your sensitive electronic components.

So, what is ESD? Electrostatic discharge is simply the static that builds up in your body which is then discharged when you touch something conductive.

Technically it’s the equalization of the difference in electrical potential of two objects.

That “shock” you feel when you walk across the carpet and touch your dog, is a great example of ESD. It’s especially worse during this time of year when the air is dryer, seems everything you touch shocks you.

That tiny little shock costs the electronics industry millions every year. It is estimated that 60% of all electronic device failures are due to static buildup and/or discharge.

Integrated circuits used to make circuit boards can be damaged by anywhere between 100 and 1,000 volts. The amount of static you buildup just by walking over carpet can be as high as 35,000 volts!

What to do? One of the most common ways to combat ESD is through the use of dissipative or conductive mats, sometimes referred to as ESD mats. These are made with materials that whisk away static from anything that touches it, much like a sponge soaks up a spill, and will typically carry the charge off the mat and through a ground wire.

Your workstation should, at the very least, include a floor mat and a table mat. They typically come in one to three layers. A dissipative rubber, vinyl, or industrial elastomer top layer and conductive middle layer are what you will commonly find in most ESD mats. Sometimes a third dissipative bottom layer will be found that will also feature a non skid surface.

Check to make sure your mats come with a good ground cord and grounding system as well.

An ESD wrist strap is also part of an ESD Safe workstation. This is a simple two-part device that connects a person’s skin to a ground. This is useful as an added measure as this device constantly dissipates any charge further preventing any discharge.

A very useful tool in an ESD Safe workstation is the Static Monitor. These devices constantly monitor the connection and static levels of the person assuring a static free workspace.

If you do a lot of walking or standing you may look into heel straps or grounds that use the moisture in your shoe as a connection to the body and a conductive rubber tread as a connection to an ESD mat or floor.

Add an ESD awareness sign and you’ve got a complete ESD Safe Workstation!

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