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| How to Read Push-Pull Testing Machine Failure Modes So You Stop Rejecting Good Bonds or Accepting Bad Ones |
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| 564 Beiträge - Alter Hase
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A push-pull testing machine produces a force number, and a force number on its own is a poor basis for a pass or fail decision. The same peak can come from a healthy bond, a partially peeled interface, or a tool that contacted the wrong surface, and if you only read the peak you will eventually reject good parts and accept bad ones. In the field, the difference between a useful result and a misleading one is almost always whether someone read the failure mode and the shape of the load displacement curve together, instead of trusting the number alone.Get more news about push-pull testing machine ,you can vist our website!
This is how we train operators and quality engineers when a bench goes into production. We will work through five steps in sequence: read the curve shape before the number, let the fracture location name the problem, rule out the four common causes of a low reading, rule out the three common causes of a high one, and finally set limits that can be defended, with a retest and a cross section closing the loop.
The short version, if you only read this far
The curve shape separates a real weak joint from a test that went wrong. The peak value cannot.
A break at the interface and a break in the wire neck are different engineering messages, even at the same force.
Low readings are usually setup. High readings are usually setup too, and nobody is motivated to question them.
A limit without an allowed list of failure modes can pass inflated results and fail honest ones.
Step 1: Read the Curve Shape Before You Read the Number
The curve explains the number. A single peak strips out every clue about how the joint behaved on the way to failure, while the shape preserves them. Four patterns cover most of what you will see on a bond bench.
A sharp rise to a clean peak, then a sudden drop. This is the signature of a brittle interface or a brittle intermetallic break. The joint carried load elastically and failed with almost no plastic warning.
A gradual rise with a rounded top. This points toward ductile behaviour. Something deformed before it failed, which usually means the bulk material gave way rather than the interface.
Early noise, steps, or a flat shelf. Steps and shelves are a setup warning: tool slip, a specimen that shifted in the clamp, or a lead that bent before the load reached the joint.
A peak immediately at the start of the run. A very early peak normally means the tool touched something it should not have, or the specimen was already loaded before the test began. Treat it as a setup error, not a bond result.
The practical value of curve shape is that it separates a genuinely weak joint from a test that went wrong. Over the years we have saved more parts by reading curves than by reading numbers, because the curve is where the setup leaves its fingerprints. Once you can recognise those four patterns, the next question is what the fracture location itself is telling you, and that message is even more specific.
Step 2: Let the Fracture Location Name the Problem
Bonds fail in four recognisable places, and each one points at a different root cause. Learning to separate them is the single highest value skill on a bond test bench, because two of the four tell you about the joint while the other two do not.
Fracture location What you see Usual root cause Engineering message
Interface separation, peel A clean lift off with one surface left bare Weak adhesion, contamination, poor surface preparation The joint never formed properly
Bulk fracture in the solder or bond Material torn through the body of the joint The joint formed well, but the alloy or solder is weak Bonding worked; material strength is the limit
Intermetallic layer fracture A brittle break inside the reacted zone Excess intermetallic growth driven by thermal history A time and temperature problem, not a placement problem
Neck or shank break A break away from the joint, in the wire or lead Tool loading point, loop geometry, or handling damage The test was the weak point, not the bond
A bulk fracture is often a good sign, because it means the interface held while the material gave way. A neck break tells you almost nothing about the joint, because the load path failed somewhere the test was never designed to probe. Before you record any force, classify the break. If you cannot say where the joint failed, you do not yet have a result you can act on. What usually stops people from classifying is not the microscope work, it is not knowing which causes to look for, and the low readings are the place to start.
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| Beitrag vom 24.10.2026 - 05:06 |
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