Alloy Junction 1952 Complete Package Sealing
# Complete Package Sealing: Curing Is a One-Time, Permanent Squeeze
Step 38 covered the risk of a void trapped inside resin that was already liquid; this step is about what happens as that same resin stops being liquid at all. Completing the cure is not a passive waiting period — a thermoset resin shrinks as it polymerizes, typically by a few percent of its own volume, and because the leads Steps 33 through 35 attached are rigid and already fixed in position relative to the device, the resin cannot simply shrink freely around them. It shrinks *against* them instead, locking in a permanent mechanical stress the moment the cure finishes — a one-time, irreversible squeeze that Step 37's thermal-cycling concern and Step 38's void-field concern never had to account for, because both of those describe effects that come and go with temperature or voltage. This one is built in for good, the instant curing completes.
## 1. Shrinkage Against a Rigid Inclusion Leaves a Permanent Residual Stress
A resin curing freely in open air would simply shrink down to a smaller, stress-free volume. A resin curing around a rigid lead or bond it cannot displace is prevented from shrinking all the way, and that prevented shrinkage shows up instead as a locked-in residual stress clamping down on whatever rigid feature is embedded in it:
where $E_{\text{resin}}$ is the cured resin's elastic modulus, $\varepsilon_{\text{shrink}}$ is its volumetric cure shrinkage strain, and $\nu$ is its Poisson's ratio. Unlike Step 37's clearance concern, which only matters at temperature extremes, or Step 38's void-field concern, which only matters while the device is energized, $\sigma_{\text{cure}}$ is present permanently, in every unit, the instant the cure finishes — it is simply a question of how large it is and what it adds to.
## 2. Real Diagram: The Resin Can't Shrink Past a Rigid Lead
## 3. Cure Stress Adds Directly to Whatever Mechanical Margin Was Already Spent
The cure-induced stress does not act in isolation on a pristine bond — it adds directly onto whatever mechanical stress Step 35 already placed on the base tab's bond root when the terminal connection was made. Because both stresses act on the same joint, the combined load the bond actually experiences after curing is their sum, not either one alone:
A unit that comfortably satisfied Step 35's own safety margin, $\sigma_{\text{bond}} < \sigma_{\text{bond,critical}}$, on the bench before encapsulation can still exceed that same critical stress once $\sigma_{\text{cure}}$ is added in — not because anything about Step 35's work was wrong, but because this step introduces a second, independent load on the identical joint that Step 35's own check had no way to anticipate. This is the real reason $\sigma_{\text{bond,critical}}$, tied all the way back to how much intermetallic Step 24's bonding cycle actually grew, remains relevant this late in the process: a thin bond that passed Step 35's check with real but modest margin can still fail only after this step's cure adds its own permanent contribution on top.
## Real Diagram: Two Margins That Were Each Safe Alone
## Complete Package Sealing's Place in the Process Lineage
Complete Package Sealing follows Step 38, Encapsulate or Enclose, which introduced the resin this step now cures permanently in place; it precedes Step 40, Apply Specified Conditioning, whose aging and thermal cycling will test whether the combined stress state this step locks in — cure shrinkage plus whatever mechanical margin Step 35 already spent — actually holds up over time. It is the third step of Phase 5 and the only step in this entire series whose governing stress, once applied, never relaxes or cycles away again: unlike Step 37's reversible thermal clearance or Step 38's voltage-dependent void field, $\sigma_{\text{cure}}$ is permanent the moment this step finishes, making it the one mechanical quantity this device will carry, unchanged, for the rest of its service life.