This product is being produced and released in the industry due to the fact the 7C-I exemption will be expiring on approximately July 1, 2016. (There is a chance the 7C-I exemption could be delayed if enough companies request an extension and an extension is approved by the EU).

A new product data sheet along with material declarations and reliability data are now available on-line at www.venkel.com.  SGS or Interek material reporting validation data (verifying all the material compositions or MDS’s) will be forthcoming within the coming months and available by the end of the year.  Besides the material differences, there are differences in the resistance ranges and in the Temperature Coefficient of Resistance (TCR) when compared to Venkel’s CR series General Purpose Thick Film Resistors.  In some cases, depending on the size and value needed, the TCR may be higher.   The wattage ratings are considered industry standard such as the 0402 and 0603 which are rated at 1/16th Watt (0.0625W) and 1/10th Watt (0.10W) respectively. 
Although the exemption is not set to expire until July of 2016, numerous customers have requested that we have a complaint alternative available now.  Depending on each company’s situation, some must have a strategy in place in order to get new products tested, verified and released.  Many companies want to get ahead of the game on this mandate so no bottlenecks or delays will occur prior to or after the deadline. 
The new CRG series resistors are available now. This series enables you to have your products fully RoHS 6/6 (if that specific resistor product line was the only commodity preventing you from being fully RoHS 6/6 compliant). Please let us know if you have any questions regarding this new product release and if samples are needed for qualification purposes and we will do our best to accommodate you
Sincerely,
Nathan Bailey

 

This is Part 3 of a Four Part Series

• Part 1
• Part 2

Hello fellow engineers and circuit problem solvers. We have a lots going on ‘round here and as we keep adding important and relevant data to our website and catalog. Just like you, there is much more to do but we are well on our way and making improvements in many areas. This month’s blog is #3 in a series of 4 related blogs regarding the testing and best practices for testing high value or high capacitance MLCC’s. This month will blog will expand on the information we have discussed and the 4th in the series will end with a general summary of all the aforementioned best practices for testing these high value MLCC’s.

What happens when you attempt to measure a high value MLCC with an LCR tester not suited (i.e.- it does not have and adequate power supply to provide the DUT the with the necessary rms test voltage) for measuring high value MLCC’s with low Z and ESR? Answer: The tester will not supply the necessary AC test voltage and it will drop below a minimum specified level to provide the DUT with enough AC test voltage giving you an artificially low capacitance reading and leading you to believe that the capacitors are out of specification. You may set the test voltage to 1.0 V but many testers will not provide the true “selected” voltage and the actual test voltage applied to the DUT will probably be in the 0.3V-0.7V range due to the low impedance. Following is a graph of a table I supplied in the previous post on this subject showing capacitor impedance at 120Hz and 1kHz and the current required to the test voltage (Arms):

 

(This post is part of a series. See Part 1 to get caught up.)

Hello fellow engineers, task masters, and problem solvers.  Hope all is going well and productive in your world. Well, it looks like Test machines and LCR meters have been at it again – not supplying the correct and adequate test voltage to a high value ceramic capacitor when undergoing testing to determine if their capacitance is within specification for these little multi-layer ceramic devices (components)]. 

 Because the current required to drive a 1KHz signal across a 10μF DUT (device under test) capacitor at either 0.5VAC or 1.0VAC may exceed the AC current capability of a typical LCR meter, it may not be best (in order to obtain an accurate reading) to measure capacitance values of 10μF or above at 1KHz, as this may cause the test voltage at the DUT to be reduced significantly below the set value, leading to erroneously low measured capacitance. This is certainly the case for values from 22uF to 220uF but the 10uF seems to be a special case as all manufacturers call for the 10uF to be tested at 1V  RMS and 1KHz.  I know you have heard the phrase “ if all else fails – read the directions – we’ll, in this case it would be the owner’s manual of your capacitance meter.  Reading it will help you understand the current capability of its power supply. If the current capability of the power supply of your meter exceeds approximately 70 mARMS, it may be suitable to use it to measure capacitance of 10μF capacitors at 1 KHz. Otherwise, it may not be suitable to test at  1KHz, and may be necessary to measure capacitance at 120Hz in order to obtain the actual capacitance value (or at least get close to it).  I will go into the 10uF case at another time but for now, here is some data that will help set this all up and hopefully provide some insight into this issue (or maybe it’s better termed as an “on-going challenge”).

The impedance values at two common measurement frequencies (120Hz and 1000Hz) for the same capacitance values is indicated in Table 1 below:

   Table 1.  Impedance of a MLCC at 120Hz & 1KHz

Figure 1. Z vs. frequency for MLCC’s for a large range of capacitance values

So what does this all mean?  How can it help me understand my test set-up and results? What should I do to get better and more accurate results?  Questions that we will discuss and go into further detail next time. For now, keep solving those problems and remember, there is no “failure”, only feedback.  It may be bad or good feedback, but it’s still feedback.

Until next time.

Set-up, measurement, accuracy, test method, result; Words that test engineers know and live by.  We all want accurate results and if you ask 10 test engineers, you might get 10 different answers on how to get there.   When you tell a test engineer that his or her results are incorrect, they may take offense and push back and say they’re ones that are correct and its your products that are out of specification. 

 This is what we find when encountering measurement or correlation issues when endeavoring to measure high value (typically considered to be > 1uF) Multi-Layer Capacitors or MLCC’s.  The inability to accurately measure high value MLCC’s has been an issue in our industry for years with the advent of high value MLCC’s, the issue does not appear to be going away anytime soon. This is due to the fact that many capacitance testers and LCR meters used throughout the industry are not designed to, nor have the capability to correctly measure capacitance of high capacitance (Hi-Cap) MLCCs. This is the case whether we are measuring capacitors at 1 VAC and 1 KHz or 0.5 VAC and 120 Hz. The inability to correctly measure high capacitance MLCCs is due to two reasons. First, many LCR meters do not have the capability of supplying enough current to the capacitor being tested at 1KHz and 1 VAC, resulting in a reduced measurement voltage which results in an artificially reduced capacitance reading. Second, Hi-Cap MLCCs typically utilize Class 2 dielectrics (e.g. X5R, X6S, X7R, X7S, etc.) that are sensitive to test voltage in the sense that changing test voltage results in change in capacitance. Since Class 2 dielectrics are typically made with ferroelectric dielectric materials that are non-linear in behavior with respect to test voltage, this change in capacitance will occur. These two reasons plus the ageing phenomenon (discussed in an upcoming Blog) exacerbates the issue and explains why it is essential to ensure that you apply the correct test voltage to the MLCC when measuring or testing a capacitor and trying to obtain its actual capacitance value. Incorporating the right bridge and applying the correct parameters is essential in obtaining an accurate capacitance measurement.

 To ensure that capacitance is correctly measured, each capacitor must be tested under the correct conditions. The correct conditions for measurement depend upon the capability of the measurement equipment as well as the nominal capacitance to be measured. Since Capacitance measurements are typically performed in the low range of the frequency scale around 120Hz-1KHz, the capacitive reactance (X_C) typically dominates the impedance equation, and Z may be estimated from the relationship:

From this relationship, it is clear that the impedance of a capacitor is dependent upon frequency and capacitance value. So why does the electronic industry make a standard to measure a 10uF MLCC at 1KHz but a 15uF at 120Hz?

In my next post I will discuss this in more detail and demonstrate how that works in the form of a graph and some additional data.  Then,  I will continue with providing information and data to support the theory that MLCC’s with the value of 10uF should also be tested at 120Hz and not 1kHz. This should “stir the pot” a bit as I have encountered numerous instances where this is the case when older test equipment is used throughout the industry.  Some customers have re-evaluated their test frequencies based on cap value and the type of test equipment they have and have done so with good success.

 Hope to see you next month and as you know – “Engineers make the world go around! ”^TM