Tack
Tack turns up in 3 fields: adhesives, PCBs, geosynthetics. Here is what it means to the people in each one.
Tack in adhesives
The stickiness of an adhesive surface: how quickly it grabs another surface with light pressure and short contact.
Tack defines PSAs and matters for contact cements and hot melts. It is measured by loop tack, where a loop of tape is lowered onto a plate and pulled off, by probe tack and by rolling ball tests. High tack helps labels and tapes grab on fast lines but can make positioning hard. Tack and peel are separate properties, and a tape can have one without much of the other.
"Loop tack is way down on the new tape lot, the labels are flagging before the box leaves the line."
Tack in PCBs
To solder one or two pins of a part first to hold it in place before soldering the rest.
Tacking a part means fixing it in position with a little solder on one corner pin or one end, checking alignment, and only then soldering the remaining pins. It is the standard hand-soldering approach for fine-pitch ICs and chip parts. A tacked part can still be nudged by reheating that single joint, which is far easier than shifting a fully soldered one.
"Tack the corner pin of the QFP, check all four sides line up, then drag solder the rest."
Tack in geosynthetics
To spot-weld overlapped geomembrane with a hot-air tool so it stays aligned before the final extrusion weld.
A hand-held hot-air welder melts small spots or a light continuous line along the overlap, holding the sheets together while the gun lays the bead. Tacking is used around patches, boots and detail work. It carries no design strength, and heavy tacking that scorches the sheet is a defect in its own right.
"Tack the patch down all the way around first, then come back with the gun."