surface barrier 1953 inspect the completed assembly

# Inspect the Completed Assembly: Two Risks Between Leads, Not One

Every concern this process has addressed since step eleven was about getting something right inside the device — alignment, timing, contact formation, bonding budgets. This inspection checks something categorically different: whether the two finished leads, now routed out of an assembly built around a membrane only a few micrometers thick, are safe both electrically and mechanically now that the device is complete. A device that passed step twenty-one's gain measurement can still fail this inspection in either of two independent ways this process has never had to check together before.

## 1. Lead Separation Still Has to Hold Off the Device's Own Operating Voltage

$$V_{\text{breakdown}} \approx E_{\text{air}} \cdot d_{\text{separation}}$$

As in every earlier device this project has documented, the air gap between the emitter and collector leads sustains a voltage roughly proportional to its own length, scaled by air's dielectric strength $E_{\text{air}}$. A lead separation adequate for a bench continuity check can still be inadequate once the device is biased at its full rated collector voltage — identical physics to every prior series' lead-clearance concern, unaffected by anything specific to jet-etching or electroplating.

## 2. Real Diagram: Electrical Clearance Is Only Half of What This Step Checks

Lead Clearance Is the Familiar Check; Membrane Stress Is the New One this device adds a risk no bulk transistor in this project ever had to inspect for electrical clearance emitter lead collector lead same check as every prior series membrane stress from lead routing a lead pulling across the thin region risks the fracture limit from step sixteen a device can clear the left check completely and still fail the right one

## 3. A Lead Routed Across the Membrane Reintroduces Step Sixteen's Fracture Limit

$$\sigma_{\text{membrane,routing}} = \frac{T_{\text{lead}}\sin\theta_{\text{lead}}}{A_{\text{membrane}}} < \sigma_{\text{fracture}}$$

A lead's own tension $T_{\text{lead}}$, if routed at an angle $\theta_{\text{lead}}$ that carries any component of force across the membrane rather than purely along the rigid frame surrounding it, reintroduces exactly the fracture-stress limit step sixteen's rinse procedure was built to respect — except now the stress source is permanent mechanical routing rather than a transient rinse jet. This is the check no bulk-wafer device in this project's histories has ever needed, because no earlier device's finished geometry included a membrane thin enough for its own leads to threaten it after assembly is otherwise complete.

Lead Angle Decides Whether Routing Threatens the Membrane tension along the rigid frame is harmless; tension across the thin region is not lead routed along the frame θ_lead small, stress negligible lead pulling across membrane θ_lead large, risks fracture limit this is checked by physical inspection, not by step 21's electrical test a device can gain-test perfectly while still having a lead routed dangerously this is the last chance to re-route a lead before encapsulation locks the geometry

## Inspect the Completed Assembly's Place in the Process Lineage

Inspecting the completed assembly is step twenty-two of Philco's surface-barrier process, immediately after the contacted element has been checked for gain and before the device is encapsulated. It carries forward the lead-clearance check this project's earlier series already established, and adds a second check unique to this device's own geometry: confirming that neither lead's physical routing places tension across the membrane that could crack it after assembly is otherwise finished. Step twenty-three, encapsulating the device, is the step that permanently locks in whatever this inspection confirms or fails to catch.

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