Point Contact Transistor Attach Point to Spring ARM
# Attach the Formed Point to a Spring Arm: The Mechanism Step 7 Already Had to Anticipate Now Actually Exists
Step 7 built a mount stiff enough to resist a spring force that, at the time, belonged to a mechanism nowhere near existing yet. Step 12 is where that mechanism stops being a design allowance on someone else's step and becomes a real, physical spring with a real stiffness of its own. The formed point from Step 11 — a wire with a shaped, solder-tipped end — gets fixed to a spring arm, and from this step forward, the force Step 7's mount had to be ready for is no longer hypothetical. It is a property of an actual object, built to a specification, that will eventually press this exact point against the germanium Step 10 finished preparing.
The spring's stiffness is not a free design choice; it is already constrained by a number Step 7 committed to five steps earlier. Step 7 only had to be rigid enough relative to a spring stiffness the process intended to use, and that intention, whatever it was, is the target this step's spring is now built against. A spring built noticeably stiffer or more compliant than what Step 7 assumed does not just change how the point presses against the germanium going forward; it retroactively tests whether Step 7's mount was actually adequate, on a mount that cannot be revisited at this point in the sequence without disassembling everything built on top of it. Step 12 therefore does not get to specify the spring purely on the point contact's own requirements — it has to close the loop Step 7 opened, confirming the mount built back then was built for the spring actually being installed now.
This attachment carries two different jobs through the same joint, the same pairing of risks Step 7's lead-and-mount already established. The joint between the formed point and the spring arm has to conduct the point contact's current reliably, because this is the electrical path the emitter or collector current will travel every time the device operates, and it has to transmit the spring's mechanical force to the point without absorbing or dulling it, because a joint that flexes under load quietly subtracts from the force reaching the germanium in exactly the way a compliant mount would. A joint that is mechanically excellent but electrically marginal delivers inconsistent contact resistance at the point; a joint that conducts beautifully but flexes under spring tension delivers an unpredictable, understated contact force. Neither failure is visible by inspecting the other requirement, which is the same trap Step 7 already laid out for the mount and the lead bond.
A small attachment error near the spring's base becomes a large positioning error at the tip, which is the one part of this step that has no analogue earlier in the sequence. Because the spring arm acts as a lever, a slight misalignment in how the formed point is fixed to it is magnified by the arm's length by the time the tip reaches the germanium — a joint that looks acceptably aligned at the point of attachment can still land the tip outside the narrow spacing window Step 1's diffusion-length argument and Step 3's roughness target were both built around. Every spacing-sensitive decision earlier in this sequence assumed the point would actually arrive where it was supposed to; this step is the first one where getting that arrival wrong is a real, physically magnified risk rather than a measurement error.
| Step | Process operation | Input | Output | Specification | Constraint |
|---|---|---|---|---|---|
| 12.1 | Confirm the spring stiffness target committed to by Step 7's mount design | Step 7's mount stiffness specification | Spring stiffness target | Target stiffness consistent with the value Step 7's mount was built to exceed | Building a spring inconsistent with Step 7's assumption retroactively invalidates a mount that cannot be revisited here |
| 12.2 | Build or select the spring arm to the stiffness target from 11.1 | Spring stiffness target from 11.1 | Spring arm, stiffness-verified | Measured stiffness within the range Step 7's mount design assumed | An unverified spring stiffness leaves Step 7's entire mechanical premise unconfirmed |
| 12.3 | Design the attachment joint to carry current and mechanical force without compromising either | Formed point from Step 11, spring arm from 11.2 | Joint design, both electrical and mechanical | Joint resistance low and consistent; joint stiffness high enough not to absorb spring force | A joint optimized for one property alone can quietly fail the other, exactly as Step 7's lead and mount could independently fail |
| 12.4 | Attach the formed point to the spring arm at the position and angle that will land the tip within the required spacing | Spring arm from 11.2, formed point from Step 11, target point spacing from Step 1/Step 3 | Point-and-spring assembly, position-verified | Tip position, once the arm is loaded, within the spacing tolerance Step 1 and Step 3 established | A small attachment misalignment is magnified by the arm's length into a large error at the tip |
| 12.5 | Measure delivered contact force and joint resistance under a representative load | Point-and-spring assembly from 11.4 | Force- and resistance-verified assembly | Delivered force and joint resistance both within the device's operating requirements | A spring with correct stiffness and a joint with correct resistance can still deliver an incorrect force if either was measured in isolation rather than together under load |
| 12.6 | Record spring stiffness, joint design, attachment position, and both measured results against this point contact's identity | Verified assembly from 11.5 | Documented point-and-spring assembly | Stiffness, joint design, position, and measurements recorded against the record started in Step 11.6 | Without this record, a later point-contact anomaly cannot be traced to this assembly step versus the point contact's own earlier fabrication |
Step 12 does not just mount a point contact on a spring; it closes a loop this sequence opened five steps earlier and opens a new one of its own. Step 7 built a mount for a spring that did not yet exist, trusting that the spring eventually built would match what the mount's design assumed. This step is the first to test that trust by actually building the spring, and it immediately creates a new, narrower requirement of its own — an attachment precise enough that a lever's natural magnification of small errors does not undo a spacing target the sequence has protected since Step 1. Nothing about this step is harder than the mechanical work in Step 7 or the solder work in Step 11, but it is the first step where a mistake at one end of the device can be measured, amplified, and felt at the other end before the point contact ever touches germanium.