A second source protects supply. Badly implemented, it doubles your engineering load and halves the attention each supplier gets.
Second sourcing is usually driven by risk: a single plant, a single line, a single set of tooling. The instinct is right. The common implementation — hand the same package to two suppliers and let them figure it out — creates a second, quieter risk: two slightly different processes producing two slightly different products under one part number.
The way through is to treat the documentation as the product. One released definition, one test procedure, one acceptance standard, and both suppliers building to it. Where a supplier needs a process-specific deviation, it is released as such rather than absorbed locally, so the difference is visible in the record.
Ramp the second source on a real product, not a token one. A supplier who has built two hundred units of a live variant is a second source. A supplier who has built one sample of an obsolete variant is a folder in your quality system.
And keep the split honest. A second source at five percent of volume will not stay qualified — the process decays, the operators forget, the fixtures go stale. Enough volume to stay competent is the price of the insurance, and it is a real price worth stating out loud when the decision is made.
— GANI Manufacturing engineering team