Motorola Corporation

Edwin L Bradley, Iii

Kingshuk Banerji

Vahid Kazem-Goudarzi

William B Mullen, Iii

Henry F Liebman

Francisco Da Costa Alves

A solder clad printed circuit board (100) consists of an electrically insulating substrate that has copper circuit traces (105), portions of which are solderable. A substantially planar layer (120) of a soldering composition is fused to the solderable traces, to form a solder pad that is not domed. The layer is composed of a mass of off-eutectic solder particles (115) that are fused together to form an agglomeration (120) having a porous structure. The solder particles are fused together by heating the off-eutectic solder to a temperature that is between the solidus temperature and the liquidus temperature of the solder. The solder is then cooled below the solidus temperature to solidify it.

Single alloy solder clad substrate

A solder paste is made from solder powder having two different alloys. The individual particles in the solder powder consist of a low melting solder coating (115) that surrounds a nucleus (120) of a higher melting solder. The low melting solder is compositionally distinct from the higher melting solder. The particles are suspended in a matrix of a solder paste vehicle, which may also contain a fluxing agent. In one embodiment of the invention, the low melting solder is an alloy of 43% tin, 43% lead and 14% bismuth, and the higher melting solder is an alloy of 52% tin, and 48% bismuth.

Solder paste

A soldering process using two different types of solder alloys is disclosed. The first solder alloy (115) undergoes a solid-to-liquid transition at a first temperature. The second solder alloy (120) undergoes this solid-to-liquid transition at a second temperature, the second temperature being greater than the first temperature. The soldering composition is deposited (20) on a substrate (100) having solderable portions (105) and is heated to a temperature that is above the first temperature but below the second temperature (32). During this time, the first solder alloy liquifies, while the second solder alloy remains solid. The soldering composition is subsequently cooled (40) to solidify the first solder material. A part or electronic component is added (80) to the solidified solder material and the solder materials is again heated above the second temperature (30) in order to reflow the solder and form a metallurgical bond between the substrate and the electronic component.

Soldering process

A method of applying a tacking agent to a printed circuit board. The printed circuit board (10) has a number of solder pads (12), and each solder pad is preclad with a layer of solder (14) between 0.02 and 0.3 mm thick. A plastic film (16) is temporarily adhered to the printed circuit board by a pressure sensitive adhesive. The plastic film has a number of apertures (22) that correspond to the solder pads, and is positioned so that the apertures in the film expose the solder coated pads. There is a breakaway tab (20) on the plastic film that is used to peel the film from the printed circuit board in a later operation. The film is roller coated with a high viscosity tacking agent (30) so that a layer of the tacking agent is applied to the exposed interconnect pads. The plastic film is then peeled cleanly away from the printed circuit board using the breakaway tab, leaving the tacking agent only on the solder pads. An electronic component (35) can then be placed on the printed circuit board in contact with the coated solder pads. The printed circuit board and the electronic component can then be heated to reflow the clad solder and form a solder joint between the solder pads and the component.

Method of applying a tacking agent to a printed circuit board

A soldering process uses two or more different solder alloys. A first solder alloy (115) that undergoes a solid-to-liquid transition at a first temperature is coated (20) onto the solderable surfaces (105) of a printed circuit board (100). A solder paste (120) that undergoes this solid-to-liquid transition at a temperature greater than the first temperature is deposited on the coated solderable potions, and is heated to a temperature that is above the first temperature but below the second temperature. During this time, the first solder alloy liquifies, while the solder paste does not. The first solder alloy wets to the individual particles in the solder paste, and alloys to the solderable surfaces and the solder particles in the solder paste. The soldering composition is subsequently cooled (40) to solidify the first solder material, forming a solid and substantially planar coating on the solderable potions of the printed circuit board.

A solder preform (250) has solder particles of one alloy (210) arranged within a matrix of a second solder alloy (200). This arrangement forms a structure having the desired predetermined shape of the solder preform. The solder particles comprise one or more of the following elements: tin, lead, bismuth, indium, copper, antimony, cadmium, arsenic, aluminum, gallium, gold, silver. The particles have a predetermined melting temperature. The second solder alloy is compositionally distinct from the solder particles, and has a melting temperature that is lower than the melting temperature of the solder particles. The solder particles may comprise about 88% by weight of the solder preform, and the second solder alloy comprises about 12% by weight of the preform.

Multiple alloy solder preform

A solder-clad printed circuit board (100) has solder particles of one alloy (120) arranged within a matrix of a second solder alloy (115). This arrangement forms a flat structure that is alloyed to the solder pads (105) on the substrate. The solder particles (120) have a predetermined melting temperature and are made from one or more of the following elements: tin, lead, bismuth, indium, copper, antimony, cadmium, arsenic, aluminum, gallium, gold, silver. The second solder alloy (115) is compositionally distinct from the solder particles, and has a melting temperature that is lower than the melting temperature of the solder particles. The solder particles may comprise about 88% by weight, and the second solder alloy may comprise about 12% by weight of the solder cladding.

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Sunrise, FL, United States of America

Edwin L Bradley, Iii