Planar Process 1959 Measure Reliability Mesa Baseline

# Measure Reliability Against the 1958 Mesa Baseline: Putting a Number on What Step 1 Promised

## 1. Why This Measurement Finally Turns an Argument Into a Ratio

This step runs the identical accelerated life test the 1958 series used at its own Step 8 — elevated temperature and humidity, the same stress conditions, the same failure-mode analysis by cross-section — on a batch of these planar devices, specifically so the result can be compared directly against the 1958 mesa line's own recorded failure rates rather than judged in isolation. Every argument this series has made since Step 1 has been geometric and structural: the junction stays covered, the margin stays positive, the undercut never eats through. This step is where those structural arguments finally get translated into the one unit that actually matters to a customer — a failure rate, measured the same way, under the same stress, as the number the 1958 series already produced. Because the planar device's surface leakage mechanism Step 7 confirmed was never activated in the first place, the comparison reduces to a specific, quantifiable ratio:

$$\frac{\lambda_{\text{mesa}}}{\lambda_{\text{planar}}} \approx \frac{I_{\text{surf, mesa}} + I_{\text{bulk}}}{I_{\text{bulk}}}, \qquad I_{\text{surf, mesa}} \gg I_{\text{bulk}}$$

where $\lambda$ is the measured failure rate under the shared stress condition, $I_{\text{surf, mesa}}$ the surface leakage contribution the 1958 series characterized at its own Step 6, and $I_{\text{bulk}}$ the leakage any clean junction carries regardless of surface condition. Because the 1958 series' own measurements showed surface leakage dominating bulk leakage by a wide margin under humid stress, this ratio is not a marginal improvement — it is close to the entire mesa failure rate, divided out, because the planar device simply never had the surface term to begin with.

The Same Stress Test, Two Very Different Results failure rate under identical accelerated stress, mesa against planar FAILURE RATE UNDER SHARED STRESS CONDITION 1958 MESA surface leakage dominates 1959 PLANAR bulk leakage only, surface term absent same test, same stress λmesa/λplanar ≈ (Isurf+Ibulk)/Ibulk, with Isurf ≫ Ibulk this is not a modest improvement; it is nearly the whole mesa failure mechanism, removed

## 2. Real Diagram: Reading the Two Failure-Mode Breakdowns Side by Side

The 1958 series' own failure-mode analysis at its Step 8 broke mesa failures into three mechanisms — surface inversion, metal corrosion at the edge, and coating delamination — all three tied directly to the exposed sidewall. This step repeats that same breakdown on the planar batch and finds all three mechanisms essentially absent, because none of them had an exposed sidewall left to act on.

The Same Three Failure Modes, Mostly Gone 1958's own failure-mode breakdown, repeated on the planar batch 1958 MESA FAILURES surface inversion metal corrosion coating delamination 1959 PLANAR FAILURES surface inversion, negligible metal corrosion, no exposed edge coating delamination, no coating used every mechanism 1958 named depended on an edge this series never produced

## 3. Why This Is the First Measurement in Either Series That Compares Across a Project Boundary

Every reliability measurement the 1958 series took — leakage characterization, life testing, burn-in screening — compared a mesa device's performance against its own internal specification or against itself over time. This step does something this project has not done before: it takes a measurement from one series and a measurement from a different series, run under conditions deliberately held identical, and compares them directly against each other. That comparison is only meaningful because both series used this project's own documented test methods, carried over without modification — the accelerated stress conditions, the acceleration-factor framework, the failure-mode cross-sectioning, all inherited intact from 1958's own Step 8. The result this step produces is therefore not a claim this series is making about itself; it is a measurement the 1958 series' own tools are making about the series that replaced it.

Step 8 does not discover a new fact about reliability; it finally gives a number to the argument every earlier step in this series has been making in words, and that number belongs to both series at once.

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