Rejection and rework of reliable connections is a plague in electronics manufacturing. Faulty inspection is often the single largest waste in electronics manufacturing.
EMS Reliability Criteria eliminates the rejects of good connections and increases the identification of real rejects.
Costs of Rejecting Reliable Assemblies
Rejecting reliable connections imposes several serious costs, including:
- Labor
- Damage (modern components are very heat sensitive)
- Defective data that is useless for statistical process management and improvement
- Longer delivery time
Why Inspectors Reject Reliable Assemblies
Why do inspectors perform so poorly? In electronics plants all over the world, we found the same cause: inspectors are confused. And who wouldn’t be confused? In the case of the most widespread workmanship standard, IPC–A–610, the inspectors are expected to memorize hundreds of pages of instructions, many of them:
- Irrelevant
- Impossible
- Badly illustrated
- Misleading
Irrelevant Criteria
No electronics plant will ever see some of the defects contained in the pages of IPC–A–610. That’s a problem for users but not the main problem involves the inclusion of “acceptable” conditions such as “preferred” and “minimum acceptable”. That extra content overwhelms the inspector who ends up believing that any connection that is not the same as the "preferred" photograph must be defective. However, photographs don't look like real solder joints and the inspector ends up rejecting randomly.
Unclear Photographs
Solder connections are shiny 3–D metal formations. Light reflects off the solder in photographs and 2–D images never look like real world 3–D objects (especially when the 3–D object involves a component that is probably quite different from the component being inspected). These issues are further complicated by the tendency to show more than one condition in a single photograph.
Impossible Interpretation Specifications
IPC–A–610 also has impossible criteria. For example, no inspector can measure the size of a solder ball relative to the distance between component leads. Neither can an inspector know if the amount of solder in a partially filled through–hole meets the specification. There are many other impossible inspection requiremnents. (This doesn't mean hole fill should be ignored. It does mean inspectors can't tell the extent of flow in a partially filled hole. The real solution is to correct the process to achieve 100% fill; it isn't hard to do.)
Misleading Implications
Ultimately, perhaps the most serious problem with the cosmetic criteria is the implication that they apply to reworked solder connections. They do not. An experienced operator can make unreliable connections look perfect, but they are still just good looking defective connections.
The Problem With Classes
In the IPC world, there are three levels of acceptability. However, a scientifically designed and managed process will always meet the Class 3 requirements. The output is perfect without costing any more than what it costs to run an inferior process.
Of course, a connection that has been touched up to meet a more rigorous class cosmetic requirement is still just a flawed connection with a pretty exterior. So true Class 3 production should not allow touchup.
EMS RELIABILITY CRITERIA
It took us years of constant refinements to create criteria that meet the intent of IPC–A–610 without the communication problems. We replaced all the photographs with 3–D computer graphic images that clearly show the condition. The conditions themselves are only what an inspector may see. The criteria are customized for each client and available in both print and digital forms. There is no reference to the acceptable conditions. And the inspector is taught to reject only conditions in the Reliability Criteria — not to reject because the connection is different from the image of a perfect connection.
EMS Reliability Criteria eliminates the guesswork of inspection. And there are many other benefits that we’d like to tell you about. For more information, please write or call (001)727–866–6502, ext. 21
