Calculations

How to Calculate the Core Metrics for Implantable Electronics and Neurodevices

Worked formulas with real units for the five calculations that run an implantable electronics line: seal yield, battery life, inspection load, cleanroom labor, and test capacity.

Implantable electronics manufacturing runs on five recurring calculations: hermetic seal yield, battery life, micro-weld inspection load, cleanroom assembly labor, and final electrical test capacity. Each one converts data you already collect, leak test logs, drain current measurements, weld counts, and standard times, into staffing and throughput numbers you can commit to. This guide works every formula with real units and a worked example sized to a typical neurostimulator line building 500 devices per week. If you want the arithmetic done for you, the Hermetic Seal Yield and Battery Life Estimate calculators on this site accept exactly the inputs used below.

Hermetic seal yield is passes divided by starts at the helium fine leak station. Yield = units passing at or below the reject limit divided by units tested. A common limit for a 0.5 cc titanium can is 1e-9 atm cc/s helium, tighter than the baseline MIL-STD-883 Method 1014 criteria because implant life targets exceed 10 years. Worked example: 500 cans welded, 11 gross leak failures on the bombing check, 7 fine leak failures. Yield = (500 minus 18) divided by 500 = 0.964, or 96.4 percent. Track it as a rolling 4 week average, because single lots of 100 to 200 units swing 3 points on sampling noise alone. The Hermetic Seal Yield calculator also folds in rework recovery, typically 40 to 60 percent of fine leak rejects.

Battery life in years = usable capacity in mAh divided by average drain in mA, divided by 8,766 hours per year. Usable capacity is rated capacity times a derating factor, commonly 0.80 to 0.85 for Li/CFx cells, covering the end-of-life voltage cutoff and self-discharge near 1 percent per year. Example: a 1,200 mAh cell at 0.82 derating gives 984 mAh usable. A stimulator drawing 9 microamps average, which is 0.009 mA, yields 984 divided by 0.009 = 109,333 hours, or 12.5 years. Average drain is a duty-cycle weighted sum: stimulation current times on-time fraction plus sleep current times the remainder. The Battery Life Estimate calculator handles the duty-cycle weighting and derating in one pass.

Micro-weld inspection load converts weld counts into inspection hours. Load in hours per week = devices per week times welds per device times inspection seconds per weld, divided by 3,600. A neurostimulator with 12 laser welds, feedthrough pins plus case seam segments, at 500 devices per week and 40 seconds per weld under a 20x stereo scope gives 500 x 12 x 40 / 3,600 = 66.7 hours, about 1.8 inspectors at 38 productive hours each. Add sampled pull testing: 5 coupon welds per lot at 3 minutes each adds roughly 2.5 hours weekly across 10 lots. The Micro-Weld Inspection Load calculator lets you mix 100 percent visual coverage with sampled destructive tests.

Cleanroom assembly labor = (units times standard minutes per unit) divided by (60 times efficiency times availability). Standard minutes come from time studies; a typical implantable pulse generator carries 85 to 140 standard minutes across kitting, stack assembly, weld prep, and encapsulation. Efficiency in ISO Class 7 rooms runs 80 to 88 percent because gowning takes 15 to 25 minutes per entry and operators exit 2 to 3 times per shift. Availability nets out breaks and training, usually 0.85. Example: 500 units x 110 minutes / (60 x 0.84 x 0.85) = 1,284 hours, or about 32 operators at 40 hours. The Cleanroom Assembly Labor calculator applies gowning and re-entry losses automatically.

Final electrical test capacity = stations times shift hours times utilization divided by test time per unit. Implant test programs are long: telemetry link checks, impedance sweeps across 8 to 16 channels, charge delivery verification, and feedthrough continuity commonly total 18 to 35 minutes. Example: 3 stations x 7.2 productive hours x 0.85 utilization / 0.42 hours per unit, which is 25 minutes, = 43.7 units per shift. Shipping 500 weekly units therefore needs 11.5 shifts, about 2.3 shifts per day on a 5 day week. Retests matter: a 6 percent first-fail rate adds roughly 30 retest units weekly. The Final Electrical Test Capacity calculator applies a retest multiplier of 1 / (1 minus fail rate).

Chain the results before committing to a schedule. Rolled throughput yield multiplies step yields: 0.964 seal x 0.985 weld inspection x 0.94 electrical test = 0.893, so 500 shippable devices require 560 starts, and every upstream load calculation should use 560, not 500. That single correction moves inspection load from 66.7 to 74.7 hours and adds most of an inspector. Input sources matter: pull yields from MES scrap codes over at least 8 weeks, standard times from timestamped device history records, and drain currents from design verification reports, not datasheets. Rerun the numbers monthly; a 2 point yield shift changes staffing needs by roughly 4 percent.

Published 2026-07-02.