One of the most common questions we receive is, “What is the difference between IPC Class 2 vs. Class 3 assembly processes?”. Since this is such a broad topic, we’ve decided to introduce a two-part series that describes some of the general differences and processes that go into building electronics assemblies to IPC Class 2 vs. Class 3 workmanship standards. This post will provide a brief introduction to the classifications, a description of what we’ll cover in Part 2, and additional resources we’ve found to be helpful with this topic.
Class 2 and Class 3 are workmanship standards as defined by IPC-A-610 for building electronics assemblies. These standards govern what is considered “acceptable” in terms of build criteria for solder joints, heel fillets, component placement tolerance and any and all things related to building an electronic circuit card assembly. Unless otherwise indicated on the production documentation, the default build standard is generally Class 2 (there is such a thing as Class 1, but we rarely see that and even if we did we’d still build to Class 2). Class 3 is a more stringent workmanship standard than Class 2, and commonly used for products that are subject to more intense reliability requirements such as those in the medical community, or products going into space.
SO…the next question is what classification does my product fall into? IPC leaves this to the OEM to decide, but they give these broad definitions as guidance:
Class 2—Dedicated Service Electronic Products
Includes products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical. Typically the end-use environment would not cause failures.
Class 3—High Performance Electronic Products
Includes products where continued high performance or performance-on-demand is critical, equipment downtime cannot be tolerated, end-use environment may be uncommonly harsh, and the equipment must function when required, such as life support or other critical systems. (2)
Other Classification Considerations
Other than the end-use of your product, there are other factors to consider when deciding which way to go on classification. For starters, there are cost implications to building a Class 3 product. Costs can vary from very little to upwards of 15%, but generally speaking the more through-hole technology on your board the greater the cost impact to achieving Class 3. Due to automation and smaller packages and tighter tolerances for surface mount technology, achieving Class 3 for SMT parts is often achieved even on Class 2 boards.
Secondly, electronics products must be specifically designed to achieve Class 2 or Class 3 as described in IPC-2221. While you can achieve many of the same specifications for Class 3 when designing to Class 2, you often can’t achieve 100% Class 3 build requirements with a board designed to Class 2. We’ll cover examples of the acceptability requirements for both through-hole and surface mount Class 2 & 3 builds in Part 2 of our series.
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Until then, here are a couple of additional resources regarding classifications: