When you think about what makes a ‘good’ electronics assembly, what are the most common expectations that come to mind? If the assembly works as intended then surely that indicates a certain level of acceptability, right? But what about the product's longer-term reliability? And what if you'd also like it to 'look good' too?
A Printed Circuit Board Assembly (PCBA) is a surprisingly complex thing. There’s the printed circuit board itself with all its material and finishes, its various components, and the solder that holds everything together. Within that, there’s also a fair amount of scope for things to be 'good', or 'bad', or somewhere in between.
For many Electronics Manufacturing Services (EMS) providers the IPC-A-610 Acceptability of Electronic Assemblies is the agreed standard that we use to define what's acceptable, and what's not, in the world of PCBA production.
The standard comprises of three classes - 1, 2 and 3. As an Original Equipment Manufacturer (OEM) it’s important that you're clear on the basic principles that separate those classes so you have a clear and realistic expectation of what the end results are going to be.
Class 1 of the IPC standards is the lowest of the Classes, and so the most 'lenient' when it comes to making allowances for potential defects.
When we think of the functionality of the electronics assembly within a simple toy, for example, the PCBA is likely to be hidden well away inside the body of the item so the quality of the solder joints or component positions may not be such a high priority.
The product is also likely to be manufactured to very tight margins (read "as cheaply as possible") so as long as the item still functions as expected (and its operational life sits within an acceptable time-frame) then that's probably going to be sufficient.
Class 2 of the IPC standards is typically the most requested for non-critical electronic assemblies where longer-term reliability is desirable, but perhaps not essential.
Class 2 does still allow for a certain degree of imperfection. Surface mount components that have been placed slightly ‘off pad’, for example, are usually still fine electrically and mechanically, even though aesthetically they may look wrong.
The highest standard of the IPC classes is Class 3, which means an electronic assembly must be built in accordance with all of the IPC criteria. This will include laminate selection, plating thickness, material qualifications, manufacturing processes and inspection. Typically, the Class 3 standard will be aimed at more critical printed circuit board assemblies.
However, achieving that standard may also come at a premium. It might be necessary to slow down the surface mount machines to ensure the desired placement accuracy (which will mean a longer build time and additional cost). It may also be necessary to make allowance for higher degrees of scrap - in cases where materials can’t be reworked - or to allow time for extra inspection or additional cleaning.
Many would argue that a reliable EMS provider will always aim to manufacture the products they build to the Class 3 standard, regardless.
Any EMS provider that is genuinely serious about compliance is also undoubtedly going to have well-established internal training programmes to promote awareness within their manufacturing facility.
Ideally too, this compliance is likely to extend not just to the inspection of the end products, but also to monitoring every process of the build. The best way to achieve this, and to maintain the standards required, will be for them to appoint in-house IPC trainers who will themselves be externally re-certified.
In the majority of cases, the IPC-A-610 standard will suffice. But there may also be situations where an OEM prefers to produce their own criteria - to either enhance, or to replace, the existing standard.
If you do choose to create your own set of guidelines, then it will be important to ensure that your EMS partner is crystal clear about your expectations from the outset. So ideally, you should reference your specific criteria on every Request for Quotation (RFQ) or purchase order that you submit.