For over 18 years, Dr. Coleman has been the vice president of technology for Photo Stencil, working closely with customers to understand their printing requirements. His efforts have resulted in several new stencil products.
I'm a little confused because your email says the components are leadless, yet at the same time you say they have 20 leads.
I am going to assume they are leadless components with 20 attachment sites.
Without seeing these devices, my suggestion would be to put solder paste on the pad sites, place the parts and reflow them in an oven.
Steven Adamson is Market Specialist for Nordson ASYMTEK. He has worked for Kodak, Motorola and Plessey, ICL in the UK. He holds five US and 2 UK patents, was awarded a HNC in electrical engineering and was 2008 President of IMAPS.
Leadless devices can bridge without proper stencil design. There is a design formula used to determine proper deposition to wet the pad, create a good joint, and avoid bridging. Once rework becomes necessary, there are two ways to deposit paste. Print the board or print the component.
For printing the board, a small stencil could be made to clear neighboring devices that have already been loaded. This method has some challenges, such as registration issues and squeegee room.
The simplest method would be to use a component printing fixture and stencil to deposit paste on the component leads (similar to a BGA re-balling fixture). Then, place the component and reflow.
Stephanie Henninger is the Director of Technical Services & Marketing for Integrated Ideas & Technologies, Inc., a premier manufacturer of SMT stencils. She has been instrumental in the stencil design and technical support.
