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Browse Prior Art Database

Shielding Pattern with Solder Paste

IP.com Disclosure Number: IPCOM000004579D
Original Publication Date: 2001-Feb-22
Included in the Prior Art Database: 2001-Feb-22
Document File: 2 page(s) / 99K

Publishing Venue

Motorola

Related People

J. Hermann: AUTHOR [+2]

Abstract

Shielding Pattern with Solder Paste

This text was extracted from a WORD97 document.
This is the abbreviated version, containing approximately 61% of the total text.

Shielding Pattern with Solder Paste

by J. Hermann and S. Pronto

INTRODUCTION

The development of the method for applying a pattern of solder paste on a circuit board described here was driven by the need for circuit board shielding reliability and cost concerns. The "off the shelf" surface plating processes that exist today added unnecessary cost and fabrication time at the supplier. The concept described in this paper was developed to offer an economical way to provide a comparable conductive surface as commercially available plating, but with no extra cost or processing time. This approach could also be adapted to other shielding applications that may or may not involve circuit boards.

WHAT IS THE PROBLEM SOLVED?

This requirement was driven by the need to provide a cost-effective shielding technique for a new product design. The old approach of using individual metal shields was primarily replaced by utilizing a new metal cavity approach. The practice of plating the surface of a circuit board to maintain conductive properties while in contact with the metal cavity is common and cost effective. However, manufacturing limitations prohibited the use of traditional Hot Air Solder Leveling (HASL) in our application. Organic solder preservative (OSP) printed circuit board (PCB) over bare copper was suggested because fine lead pitch components were incorporated into the design. Using the OSP finish would have left the unsoldered exposed copper to tarnish. This would, in turn, reduce the shielding effect required to meet regulatory requirements.

Several PCB surface finishes were evaluated to meet our conductive shielding requirements. Gold, silver, conductive carbon ink, and internally applied solder paste were our options. The gold, silver, and conductive carbon were eliminated because of electrical issues that resulted from galvanic reactions, cost, and/or long term reliability limitations. The solder paste option was chosen because it met all our requirements.

WHAT IS OUR SOLUTION?

The existing metal castings (cavity) form a "clam" shell design that provides the necessary RF shielding characteristics. The existing silver elastomer gasket along with the new solder paste pattern are used to sandwich the PCB and the top and bottom metal castings to make a RF electrically conductive housing. This composite system, which incorporates a unique solder paste pattern, helps address conductive and radiated RF emissions. This approach provides a cost effective, easy manufacturability, long-term reliability solution.

DESCRIPTION OF EMBODIMENTS

The basic embodiment utilizes a unique pattern of solder paste screened on to a circuit board. This unique solder paste pattern will flow in the reflow oven and coat the contact area with solder. The pattern will create a surface that is not perfectly flat. The combination of an irregular surface (that results after the sold...