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Tin Whiskers and Chip Components

Posted by Mike Randall on December 23, 2016


 What are Whiskers?
“Whiskers” are protrusions that grow from a metal film over time.  They can achieve high aspect ratios, growing to considerable lengths and may result in electrical interconnection of adjacent terminals.  This can happen when a whisker grows from one terminal to another, as in the case of fine pitch electronics, or when a whisker grows, then shears from its source and lands between two terminals interconnecting them electrically.  While this is rare, it has caused considerable concern in the electronics community.

Sn Whiskers
Tin whiskers are Sn protrusions that grow from a tin film.  They may occur on the terminals of chip components such as multilayer ceramic capacitors (MLCCs), chip resistors, chip inductors, varistors, etc.  They are observed much less frequently than in the past as Sn finishes have evolved as manufacturers’ knowledge of Sn whiskers and how to avoid them has developed.  

The micrographs above illustrate Sn whiskers at three different magnifications.  At lower magnification (left), they may appear as “fuzz” on the surface of the terminations.  At increased magnification (center), they may present as high aspect ratio protrusions or “whiskers” that grow over time.  At high magnification (right), they typically appear striated on the exterior.  Some of the striae may also have horizontal ridges which have been associated with thermal cycling or other episodic events resulting in whisker growth. 

How They Form
Formation of Sn whiskers is related to stress (usually compressive stress) within the film from which they propagate.  Stress can be caused by several different sources, such as residual stress from the film deposition process (typically electroplating), or from the growth of intermetallic (IMC) phases below the surface of the film as described in a previous post on this blog, or by thermal cycling, or by bending stress in plated leads in the case of leaded components, or the like.  These stresses act to extrude the whiskers out from the plated film.  Subsequently, much effort has been expended in learning how to reduce or eliminate these film stresses in electroplated Sn films.

Where They Occur
Sn whiskers associated with reflow mounted or wave solder mounted chip components are rare because the stresses formed in the electroplated tin film during the plating process are relieved during the soldering process.  They are more common when the mounting technique used does not provide an opportunity for stress relief, such as when mounting with conductive epoxy, and conductive epoxy mounting is mainly where Sn whiskers have been observed in relation to surface mounted chip components.

Sn whiskers have also been observed in unmounted chip components.  This was more prevalent in the early days of conversion from Pb/Sn finishes to Sn finishes for RoHS, but is much less frequent in contemporary chip components as manufacturers have developed low stress Sn finishes through the development of low stress tin electroplating chemistries and processes.  These electrodeposited film chemistries are typically low in carbon and other impurities, such as Zn, and are “matte” in appearance due to relatively large and uniform Sn grain size (typically ~5 µm on average).  With these developments suppliers have been successful in eliminating the incidence of harmful Sn whiskers.  

Solutions and Conclusion
Through development of low stress plated Sn finishes, the worry of Sn whiskers has been eliminated with regard to chip components, if you use a supplier who has conquered plated film stress.  Sn whiskers will also not likely be an issue if you use a solder reflow process or wave soldering to mount your chip components.  If you use conductive epoxy mounting and you still observe Sn whiskers, you may want to heat treat the chip components using a mild heat treatment near the melting point of Sn (~232C).  Use of conformal coating on assemblies will also eliminate whisker-related problems.  I hope that helps.  May you never see another Sn whisker in your assemblies…TTFN!     ;  )   

* Micrographs courtesy of NASA 



Tags: inductor, Resistor, RoHS

Venkel's New "Green" RoHS 6/6 Resistor

Posted by Nathan Bailey on September 16, 2014


Venkel Ltd. just released the new CRG – RoHS 6/6 “Green” resistor new product offering this month on September 3rd, 2014.  This new resistor series is a general purpose Thick Film Resistor.  It incorporates new construction materials whereby Lead in the glass and Lead Oxide in the resistive element is now eliminated.  The glass frit contained within the resistive element (RuO2) no longer contains any Lead or Lead oxide and will meet the RoHS 1000ppm or 0.1% threshold without taking the 7C-I exemption. 

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
Nathan Bailey

Tags: CRG, Resistor, RoHS, thick, film, CR, RoHS 6/6

RoHS Regulations Extend to Medical and other Applications

Posted by Chris Gutierrez on August 13, 2014


For those of you who are in the field of Medical applications, have you heard that RoHS has extended the scope to cover 8 medical devices along with 9 monitoring and control instrumentations? If you didn’t know, pay close attention because this is for you. If you did know, then congratulations!  You probably have everything under control and things are sailing smooth for you, or we hope things are going smooth for you!

As of July 22, 2014 the Restriction of the use of Hazardous Substances (RoHS) , was extended to Medical and Monitoring and control instruments. These devices were not previously required to comply with RoHS guidelines according to EU directive 2011/65/EU.

With this extension of RoHS now covering these medical devices it means that going forward you must comply with the regulations set by the EU. This could be a stressful time for those who may have delayed the process of adding suppliers to their AVL. If you were proactive as I mentioned above, as I assume all of you reading this were, then you’re standing in pretty good shape. If you are reactive then my friends you might not be having a great time right now. As compliance people it can be very difficult some times to stay up with all the changing regulations and guide lines.  I guess it’s the cost of trying to make the world a better place to live. It’s my opinion that the more and more electronics continue to be a bigger part of our lives the more the scopes of RoHS and other environmental compliance regulations will change and broaden.

Here is a list of the devices now included in abiding by all RoHS regulations.

  • Smoke detectors
  • Heating regulators
  • Cardiology
  • Thermostats
  • Measuring, weighing appliances for household or laboratory equipment
  • Other monitoring and control instruments used in industrial installations
  • Radiotherapy equipment
  • Dialysis
  • Pulmonary ventilators
  • Nuclear medicine
  • Analyzers
  • Freezers
  • Fertilizations tests
  • Appliances for detecting, preventing monitoring, treating alleviating illnesses, injury or disability
  • Laboratory equipment for in-vitro diagnosis (although this extension does not currently apply to in-vitro diagnostic devices until July 22, 2016)

If you manufacture any of these devices, take a look at our line-up of surface mount components. All Venkel products are fully compliant with current RoHS2 guidelines.


Tags: RoHS

Compliant or not Compliant? That is the Question

Posted by Chris Gutierrez on June 18, 2014


When it comes to being RoHS2 compliant (also known as RoHS Recast) many people want to know if their company is compliant. The question is do we really know what "compliant" means? When RoHS was first introduced to the electronics industry back in 2003 there were exemptions that could be used and certain applications didn’t have to comply with RoHS directives set by the EU. If you don’t know RoHS currently, you will be surprised to learn things have certainly changed. Whether we agree or disagree on being compliant, it’s time to confirm our compliance status.

What are you getting at?

Since 2010 several changes have been made to RoHS. We all know this now as RoHS2 or RoHS Recast. When RoHS2 went into effect, certain applications that were exempt by RoHS regulations and directives in 2003 are now required to comply with the 2010 directives. That meant a lot of part number changes for OEMs and CM’s. Not to mention electronic component manufactures had to change certain exemptions. For example: For lead in the ceramic of the resistive element in 2003 we used exemption No. 5. The new exemption is 7c-I per the Directive 2011/65/EU of the European Parliament. This too will change very soon if extensions are not filed for the use of lead in electronic components. The exemption is currently set to expire in July, 2016.

We have started to see an increase in requests from manufactures requesting a plan of action for fully compliant parts.

Fully compliant?

I will take a little time to help clarify what the difference between being "fully compliant" and "compliant" with RoHS is.

Venkel is currently compliant with RoHS directives. We do however; claim an exemption for our Thick Film Resistor products. Our other products such as Capacitors, Inductors, Ferrite Beads and Thin Film Resistor products are fully compliant.

Fully compliant means products do not need an exemption in order to comply with RoHS directives and regulations.

So when you're asked if your company is fully compliant with RoHS or if you have a timeline for full compliance, what they are really asking is when will you not need to claim an exemption for your parts that currently claim an exemption. In most cases it’s the use of lead in products that's the issue, specifically lead found in the ceramic glass of the resistive layer. If lead is still needed you can still comply by being under the allowable threshold of 1000pm or 0.1%.

What this means for the industry

Currently we are in the early stages of knowing if extensions will be granted or if we will have to be fully compliant. With this uncertainty, manufacturers are preparing for having to be fully compliant. This means cost will go up, lead times may increase and part number changes will be inevitable. This is going to be a nightmare for those that are not getting a head start and requesting information on fully compliant products. You might be telling yourself that going to fully complaint parts will not happen in 2016, and while that may be true, it doesn't mean it won’t happen eventually.

There is one thing that we have to keep in mind. These regulations were put in place to create a safer and healthier environment. Just because it doesn't get passed in 2016, just means people need a little more time to make the transition. Some factors might be cost, as well as other changes that are going to come with this transition.

What is Venkel doing?

Venkel is in the final stages of having a fully compliant Thick Film Resistor that is equivalent to our General Purpose Thick Film Resistors. Our official target date for our data sheets to be ready is September 1, 2014. At that time you will also be able to get samples. Production quantities will be available starting October 1, 2014.

If you’re in the process of becoming fully RoHS compliant I wish you the best in the endeavor, we're here to help in any way we can. Rest assured, we are all in the same boat. The cause is a good one though: trying to make the world a safer and healthier place to live for the next generation. 

(Stay tuned for RoHS 2 resources, including an infographic and cheat sheet coming soon.)

Tags: compliant, RoHS, RoHS2

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