Point Contact Transistor Place Collector Near Emitter
# Place the Collector Point Near the Emitter Point: The Number Every Earlier Step Only Talked About
Step 1 argued that diffusion length has to exceed point spacing. Step 3 ground the contact face to a roughness standard set by that same spacing. Step 12 warned that a small attachment error gets magnified into a tip-position error at that spacing. Step 13 seated one point — the emitter — against the germanium and proved, for the first time, that a point contact and the conditioned surface could actually work together under load. None of those steps, including Step 13, ever had to produce an actual spacing value, because none of them involved two points at once. Step 14 is the step where that number stops being a design assumption and becomes a physical fact: the collector point goes down near the emitter, at a distance this entire sequence has been protecting since its very first operation.
Placing the second point is not a repeat of Step 13 with a different name; it introduces a hazard Step 13's single-point seating never faced. Seating the emitter alone meant bringing one spring-loaded assembly into contact with an inert germanium surface, which could not push back electrically and was damaged only by excess mechanical force. Seating the collector means bringing a second spring-loaded assembly into close proximity with a surface that already has a live, seated point contact on it — close enough that the mechanical shock of seating the collector can disturb the emitter's own seating, and close enough that any premature or stray contact between the two points, before final position is confirmed, risks a short or an uncontrolled interaction neither point's individual specification ever had to account for. The risk this step manages is not a bigger version of Step 13's risk; it is a genuinely new one, created by the mere presence of a second point sharing the same small region of the same surface.
The collector's position is defined relative to the emitter, not the other way around, and that ordering is not arbitrary. The emitter's job is to inject carriers into the germanium; the collector's job is to gather what survives the trip. There is no way to define a useful collector position before an emitter exists to measure the distance from, which is why Step 13 seated one point first and Step 14 places the second one near it rather than placing both simultaneously or placing the collector first. This ordering mirrors the device's own carrier-flow logic rather than being a convenience of assembly sequence — the geometry of this step follows the same asymmetry between injection and collection that Step 1 established when it chose which carrier species the device would depend on.
| Step | Process operation | Input | Output | Specification | Constraint |
|---|---|---|---|---|---|
| 14.1 | Confirm the emitter's seated position and tension remain stable before beginning collector placement | Seated emitter assembly from Step 13 | Confirmed-stable emitter | No detected drift in emitter position or tension since its own Step 13 seating | Beginning collector placement against an already-unstable emitter compounds one unresolved problem with another |
| 14.2 | Bring the collector point assembly into the vicinity of the emitter at minimal mechanical disturbance | Confirmed-stable emitter from 13.1, verified point-and-spring assembly for the collector | Collector positioned near, not yet touching, the emitter's region | No measurable disturbance to the emitter's position or tension during this approach | A heavy-handed approach risks undoing the stability just confirmed in 13.1 before the collector even makes contact |
| 14.3 | Measure the actual separation between the emitter and the approaching collector before seating the collector | Collector positioned near emitter from 13.2 | Measured pre-seating separation | Separation measured against the diffusion-length-derived target from Step 1 | Seating the collector before measuring its position converts a correctable approach into a committed, harder-to-adjust result |
| 14.4 | Seat the collector point at the verified separation, applying tension per the same bounds Step 13 established for a single point | Measured separation from 13.3, collector point-and-spring assembly | Seated collector, at target separation | Separation within Step 1's diffusion-length-derived tolerance; tension within the bounds Step 13 established | A collector seated at the right tension but the wrong separation still fails the device's core operating requirement |
| 14.5 | Re-verify the emitter's position and tension after the collector is fully seated | Seated collector from 13.4, previously confirmed emitter from 13.1 | Both points verified, jointly | Emitter position and tension unchanged from the state confirmed in 13.1 | A disturbance missed during the approach in 13.2 can still surface only after the collector is fully seated |
| 14.6 | Record the final separation and both points' verified states against each point's own provenance | Jointly verified assembly from 13.5 | Documented two-point assembly | Separation, and both points' tension and position, recorded against each point's own record from Step 11.6/11.6 | Without a joint record, a later device failure cannot be attributed to the emitter, the collector, or the separation between them specifically |
Step 14 does not place a second point; it completes a measurement the first twelve steps had been setting up without ever being able to take. Step 1's entire argument rested on a comparison between diffusion length and point spacing, but no step before this one could produce the spacing side of that comparison, because no step before this one had two points on the same face at once. This is the operation where that comparison finally becomes checkable rather than assumed, and it carries a real risk none of the single-point steps before it had to manage: that bringing the second point close enough to measure against the first can itself disturb the stability the first point only just achieved.