Micrologic 1960 Step 18 Screen Burn in Test Flow

# Screen and Burn In Every Finished Chip Before It Ships: A Test Flow a Discrete Transistor Never Needed

## 1. Why Testing Once at the Wafer Is No Longer Enough Once a Package Is Sealed

This step adds a second test stage after the wafer-level truth-table check Step 6 already performs: every packaged chip is run through electrical screening against its full specification and then subjected to a burn-in period at elevated temperature and bias, both before it is allowed onto the catalog shelf Step 17 just built. Step 6's wafer test catches a device or a connection that was already wrong at the moment of test; it cannot catch a device that passes every parameter that day but carries an early-life defect that only shows up after some hours of electrical and thermal stress — exactly the failure mode a single discrete transistor, soldered individually and tested in isolation, never forced a comparable burn-in step to exist for.

$$\lambda(t) \ \text{falls over the first hours of stress, then levels off}; \qquad t_{\text{burn-in}} \geq t_{\text{where } \lambda(t) \text{ flattens}}$$

where $\lambda(t)$ is the instantaneous failure rate as a function of stress time — early-life defects drive it high at the start and burn-in time has to run long enough to push past that falling region before a chip is allowed to ship, so that the failure rate a customer actually sees is the flat, low one, not the early spike this screening step exists to catch and discard.

The Failure Rate Curve This Step Screens Past burn-in runs long enough to discard the falling-rate region before shipment stress time under burn-in → failure rate early-life region, discarded here flat rate, what the customer receives burn-in cutoff a chip shipped before this cutoff would carry the falling-rate region into service

## 2. Real Diagram: Two Test Stations, Two Different Jobs

Wafer test and burn-in screening look superficially similar — both apply electrical stimuli and check a response — but they are answering different questions, at different points in the flow, against different failure modes, and this series needs both rather than either one alone.

Wafer Test, Then Burn-In, Then Shipment each stage catches a failure the other stage cannot STEP 6, WAFER TEST truth table against the function, at this moment catches: already-wrong devices STEP 18, BURN-IN SCREEN stress under temperature and bias, over time catches: early-life latent defects a chip must clear both stations before Step 17's catalog price applies to it

## 3. Why a Catalog Price Would Be a Lie Without This Step Behind It

Step 17's published price quietly promises a customer a known, low failure rate — a promise that would be false if this series shipped straight from Step 6's wafer test, since that test can only speak to a device's condition at the moment of measurement, not after installation. Burn-in screening is what lets Step 17's single printed number hold across every unit of that part number a customer ever receives, rather than holding only for whichever units happened to survive their own early life after leaving the factory floor.

This test flow also reinforces Step 7's and Step 13's yield economics in a second way: every unit discarded at burn-in is a cost already sunk, which is exactly why this series' price has to account for scrap at two stages, not one — Step 13's die-yield exponential at the wafer, and this step's early-life attrition at the package.

Take micrologic 1960 step 18 screen burn in test flow further

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