Dispensing
By Gary Helmers
VP Creative Automation
11641 Pendleton Street
Sun Valley, CA 91352
tel:818-767-6220
fax:818-767-1243
GJHelmers@creativedispensing.com

Quite possibly, no-lead will end time-pressure dispensing of solder paste, including on/off valves, syringe dispensing and rotary auger valves. The variation introduced by time/pressure fluctuation from a gradually emptying syringe will become a fatal flaw. This flaw cannot be corrected by simply adding more precise control. The change in time/pressure parameters must be estimated as the barrel volume decreases from full to empty. True piston positive displacement provides consistent volumes despite variation in the parameters of viscosity, temperature and syringe level.No-lead paste has demonstrated reduced wetability (stickiness). Most dispensing processes rely on touching paste to the substrate and in the hope that the surface tension between the paste and the substrate will overcome the surface tension between the paste and the needle tip. Dispensing technologies that deliver positive wetting help ensure that the paste stays on the substrate in the desired location. Material must be driven down the needle tube with enough velocity to cause a positive attachment between the material and the substrate. The goal is for this to happen without spitting the material at the board and without creating satellites and misshapen deposits.

Correcting the technology in the dispensing portion of the no-lead production line will allow all of the other process improvements to meet your full expectation.