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SELF-CENTERING PAD DESIGN FOR SOLDER CLADDING UNDER ROUND COMPONENTS

IP.com Disclosure Number: IPCOM000006315D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-24
Document File: 2 page(s) / 92K

Publishing Venue

Motorola

Related People

Ralph R. Kolle: AUTHOR [+3]

Abstract

With the addition of solder cladding as a viable process for PCB assembly, a new problem emerges for tubular components such as fuses, glass diodes, or melfs. Solder cladding produces crowned or rounded pad surfaces. Placement of a tubular part on top of a crowned pad will result in the part rolling off. One way to prevent this would be to flatten the pads prior to placement, but a flattening process would be extremely diff%xlt to control and would also require special equipment.

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MOTOROLA INC. Technical Developments Volume 14 December 1991

SELF-CENTERING PAD DESIGN FOR SOLDER CLADDING UNDER ROUND COMPONENTS

by Ralph R. Kolle, Kiron R Gore and Edward J. Hall

PROBLEM DEFINITION

  With the addition of solder cladding as a viable process for PCB assembly, a new problem emerges for tubular components such as fuses, glass diodes, or melfs. Solder cladding produces crowned or rounded pad surfaces. Placement of a tubular part on top of a crowned pad will result in the part rolling off. One way to prevent this would be to flatten the pads prior to placement, but a flattening process would be extremely diff%xlt to control and would also require special equipment.

  Tubular components are typically diicult to handle without this additional problem. They usually require the placement machine to be installed with special notched vacuum nozzles for accurate placement. Also, the place- ment speed of the machine occasionally needs to be reduced for these types of components in order to achieve adequate placement accuracy.

DESCRIPTION OF THE NEW CONCEPT

  A new pad design was needed for tubular compo- nents to prevent them from rolling off of the bumps created by solder cladding. This was accomplished by using a unique solder mask design. The new pad design was developed by taking the existing pad and splitting it into two separate pads by a thin strip of solder mask that ran through the center of the pad. This is shown in Figure I. The width of the solder resist strip will vary depending on the size and shape of the component.

  AtIer the cladding process, the two separate pads become two separate solder bumps. The solder bumps, which were a deterrent to component placement with a single pad, now become an aid for component placement. When the part is placed on the pads, it will nestle down between the two so...