Coupon
Coupon turns up in 4 fields: thermal spray, adhesives, PCBs, geosynthetics. Here is what it means to the people in each one.
Coupon in thermal spray
A small test piece sprayed alongside production parts to stand in for them in destructive tests.
Witness specimen, such as a flat tab, bond test button or Almen strip, mounted on the same fixture and sprayed with the same parameters as the parts. Coupons are sectioned, pulled and hardness tested so the real parts do not have to be destroyed. They only represent the parts if they are prepared from similar material and sit where the parts see the same gun path and heat.
"Clip two coupons on the fixture next to the vanes, one for the mount, one for bond."
Coupon in adhesives
A small standard test piece, usually a metal or plastic strip, bonded to check adhesive strength or prep.
Lap shear coupons, peel strips and wedge specimens are cut from the same material and given the same surface prep as production parts. Lines often bond witness coupons alongside real parts in each shift or batch, then break them to prove the process. Coupon results drive acceptance of film adhesive lots, primer batches and surface treatments.
"Bond six coupons with every batch and drop them in the oven with the parts, quality wants them broken by Friday."
Coupon in PCBs
Small test pattern built on the production panel and measured or sectioned to prove the boards meet spec.
A coupon is a test structure built on the same panel as the boards, usually on the rail, so it goes through exactly the same process steps. Impedance coupons are measured with a TDR to verify controlled-impedance traces, and plated-hole coupons are microsectioned to check plating thickness, hole wall quality and lamination. Coupons let a fabricator prove quality without cutting up real boards.
"Ship the impedance coupon readings and the microsection photos from the coupon with the boards."
Coupon in geosynthetics
Narrow strip cut across a seam sample for peel or shear testing, usually one inch wide.
Each destructive or trial sample is cut into a set of coupons, commonly five for peel and five for shear, and each one is pulled on the tensiometer. Coupons are cut with a die or template so widths are exact, since a ragged edge can start a tear and fail a good seam. The pass rule is usually a set number of coupons, often four of five, meeting strength and break-type requirements.
"Cut ten coupons off the trial weld, five peel and five shear, and keep them in order."