Every wire bond that ships into an aerospace, defense, or medical program has to answer a blunt question: how do you know it will hold? For wire bonding, the standard answer is MIL-STD-883 Method 2011 — the destructive bond pull test. It's a simple test that's easy to run and surprisingly easy to misread, because the number it produces isn't the most important thing it tells you.
What the test is
Method 2011 is the bond-strength test in MIL-STD-883, the DoD's test-method standard for microelectronics. A hook is placed under the wire and pulled until something gives; the tester records the force at failure and — just as important — what failed. The standard sets minimum pull forces by wire size and material, and the test is destructive: the pulled bond is gone, which is why it's run on samples and test coupons that ride alongside the real build.
The number is the floor. The failure mode is the story.
Two bonds can record the same pull force and describe two very different processes. A wire that breaks mid-span or at the neck — the wire itself giving up — says both welds were stronger than the wire: that's the failure you want. A bond that lifts cleanly off the pad or the lead says the weld was the weak point — and a population of lifts, even ones that pass the minimum force, is a process warning that no passing number should be allowed to hide.
“A pull test that only logs the force is throwing away half its data. Where the joint failed tells you what the process is doing; the number just tells you it passed today.”
This is the same logic we've written about for ball shear and other bond-strength tests: the failure mode carries the process learning. The force is a gate; the mode is the diagnosis.
Margin is the real spec
Passing at the minimum means the process was adequate on the day it was sampled. What a reliability engineer actually wants is margin — a distribution of pull strengths sitting well above the floor, tight enough that the tail never approaches it. On our wire-bond line we pull-test to Method 2011 and hold the process at multiples of the spec minimum — a recent de-identified 44-bond qualification averaged roughly 3.9× the required minimum. That gap between "passes" and "performs" is the difference between a bond that survives the test and a process that survives the mission.
What to ask your assembly house
- Do you pull-test to Method 2011, and at what sampling? "We can" and "we do, on every lot" are different answers.
- Do you record failure modes, not just forces? If lifts and breaks are logged as the same "pass," the data can't catch a drifting weld.
- What margin does the process hold above the minimum? Ask for the distribution, not a single number.
- Can I see de-identified data? A shop confident in its process will show you the histogram.
Pull testing is one piece of a larger discipline — bond-parameter control, inspection, and the traceability that ties every wire back to its build record. If your program needs wire bonds qualified to MIL-STD-883 on US soil, that's the standing work of our lab.