What is the IPC Definition for Uncommonly Harsh?

What is the IPC Definition for Uncommonly Harsh?
IPC 610 defines class three to include products where the end use environment may be uncommonly harsh. How is uncommonly harsh defined?
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
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Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.


Welcome to Board Talk with Phil Zarrow and Jim Hall of ITM Consulting, the Assembly Brothers. Today we are coming to you from high atop Mount Rialto at the ITM elegante ballroom.

Jim, what is our question today?

Well, interesting, it is about specs and regulations. It comes from S.M. What is the IPC definition of uncommonly harsh?

IPC 610 and other documents define class three to include products where the end use environment may be uncommonly harsh. Does anyone have guidelines for how uncommonly harsh may be defined.
  • What temperature ranges or ramp rates are uncommonly harsh?
  • What moisture, humidity, chemical types may be considered uncommonly harsh?
  • Is sunlight exposure uncommonly harsh?
  • Are particular levels of vibration uncommonly harsh?
Boy, this is interesting a question about harshness coming from a guy whose initial are S&M.

Getting to S&M's question, uncommonly harsh. To the best of our collective knowledge, which you could probably fit in a coffee cup, I do not believe that 610 calls out an actually definition of harsh.

Now understand that other generalized specs in other portions or corners of the industry such as automotive, other industrial applications like downhole drilling things like that, they probably do have sets that define harsh or define the environment.

But looking at the general term uncommonly harsh, and looking at the items that you mentioned. Well, let's take a look at it, Jim.

Temperature ranges and ramp rates potential for being uncommonly harsh. I don't think so, not with regard to 610 the actual joint. It might deal with flux residue.

There you might get into something. But that's not what 610 is about. We're talking about joint integrity.

So I don't think that a temperature range or ramp rate, thermal cycling would definitely have an affect. And again, what it is going through there. But I don't think an actual range that way. Jim, what do you think?

Well, as you said if it is subject to thermal cycling. Basically 610 is defining the physical structure of the joint, what it looks like, how big the fillets are and so forth. The biggest impact that it is defining is mechanical stress.

Thermal cycling is a big source of temperature stress. So yes, temperature range could be indirectly creating stresses which might be considered uncommonly harsh. The other thing that jumps out at me, Phil, is vibration levels.

Yes, many of the specs that you talk about, military, automotive and so forth, define very specific levels of vibration and other shock mechanical stresses that they test too. I think that goes back to the idea of IPC specs.

They are the starting point from which you base your specific needs for your specific product and its specific environment. What is uncommonly harsh may be different for different products.

There is a limit to how generic specifications can be. And we have discussed this many, many times. You can't look to them basically as Holy Scripture all of the time.

You have to look at your own application and conditions, certainly your manufacturing situations, and things like that. So yeah, I totally agree with my brother here on this. Be very, very careful.

You have to really examine, the application is what really defines it. You can't always keep a generic definition.

The other bullet point is sunlight uncommonly harsh. Not relative to a 610 solder joint evaluation.

But other IPC specs that talk about solder masks maybe that might relate there, or a moisture, humidity and chemical type.

Once again if we are talking about some of the IPC specs that relate to printed circuit board fabrication and its materials, those factors might be considered uncommonly harsh relative to the materials once again of laminates, coatings and so forth.

Very good. I think we covered it. Hopefully gave some direction on that one. We are here to help. We try.

You have been listening to Board Talk, Phil and Jim. Whatever you do, whatever kind of environment you are using your application in...

Don't solder like my brother.

And don't solder like my brother.  


Mr. Stadem stole my answer. My other stock answer is "It Depends" In this case, it depends on what industry segment you are talking about and what the end use environment will be. Medical might consider it bodily fluids and the ability to withstand autoclaving. Automotive may be heat, humidity, chemical exposure. Industrial controllers may be heat and chemically aggressive environments. Aerospace may be heat extremes and liquid water. You mention sunlight. Sunlight at the Earth surface is one consideration. Sunlight in the vacuum of space quite another.
Doug Pauls, Collins Aerospace
To quote from an experienced sage of the electronics industry, Sir Doug Pauls: Uncommonly harsh is defined as anything that is above the level of commonly harsh.
Richard Stadem, Analog Technologies Corp.
Temperature cycles of hot and cold, vibration, shock are part of hash environment. The actual temperature range, vibration or shock level will depend on the application 's requirements.
Vinh Nguyen, L3 T & RF
I am on these committees.Class 3 items are critical on demand. If they fail people die. Class 1 is designed to function. A cheap disposable phone would be Class 1. A smartphone though would be class 2. Class 3 would be satellite phone which could be used in harsh environments such as a jungle or desert. If it failed then people could die. This then brings in Space where there is some initial discussion to bring in mission critical or extremely harsh environment which could include deep sea.
Steve Fribbins, CIT, Fribbins Training Services
This falls into the definition of Specialized Designs. Refer to IPC A-610 Revision G section " ... Often unique definition is necessary to consider the specialized characteristics... For classes 2 and 3 the criteria shall include agreed definition of product acceptance."
Bruce Whitlock, Trimble Military & Advanced Systems
Another "uncommonly harsh" environmental concern is chemical. High sulfur or ammonia environments may require specific PCB surface finishes, conformal coatings, or protective enclosures in addition to careful part and PCB material selection.

The elevated temperatures found in "down-hole" oil and gas drilling applications probably also qualify as "uncommonly harsh" but, as noted, this should be specified by the designer in the purchasing or assembly documentation and not defined by a CM or EMS provider.
Jon Ashton, Vergent Products
In addition to vibration levels, and frequency, a high impulse shock value is commonly used.
Erik Quam, Schlumberger, USA

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