Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2001-07-30
2004-06-01
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S085190, C228S033000
Reexamination Certificate
active
06744003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic spot soldering machine, and more particularly to an automatic soldering machine used for high volume assembly operations of components such as PC boards, electrical terminals, and the like.
2. Description of Related Art
Many attempts to develop general-purpose automatic spot soldering equipment have been made in the past, but these attempts have not been entirely successful. This is evidenced by the large number of types of machines and methods presently used such as induction, laser, resistance, open flame, hot air, molten solder, infrared, electrical resistance, and hot iron systems. Each method of heating the soldered parts and melting the solder and flux have advantages and serious disadvantages which exclude any specific type of machine for usage on a wide variety of parts.
The most prevalent systems-consist of a metal tip that is heated to a pre-selected high temperature by any convenient heat source such as an electrical resistance element.
Solders that are predominantly used typically melt at about 400° F. Non-corrosive fluxes activate at 400° F. to 600° F. and rapidly decompose at temperatures over 600° F.
The most convenient method of providing the solder and flux is in the form of a solder wire containing a core of rosin flux.
Solvents used in fluxes vaporize at about 200° F. and do so quite explosively at temperatures over 600° F. This splatters flux and solder particles adjacent to the tip. The solder tip temperature for fast and good saturation of parts is usually desired to be over 800° F.
In spite of good vacuum systems, the solder/flux sputter and condensation of the flux vapors collect on the mechanical components that are in close proximity to the solder tip. The condensed flux is tacky when warm and solid when cold. This adversely affects the motion of mechanical components.
At solder tip temperatures over 600° F., the solder coating on the metal tip periodically becomes removed, which seriously reduces the heat conduction and possibly produces defective parts. Recoating the tip with solder requires tip cleaning motion with a cleaning pad, which interrupts a production line sequence.
A typical cycle sequence for soldering consists of: 1) lower the hot solder iron on top of the part(s); 2) feed the solder wire point against the side of the hot solder tip, at the interface of the tip and part; 3) dwell in this position until the part(s) are heated to over 400° F., which allows the flux to react and the molten solder to saturate the part(s); and 4) remove the solder iron to the initial position.
Another typical sequence is to: 1) feed the solder wire out between the part(s) and solder tip; 2) lower the solder tip onto the solder wire; 3) melt the solder (and flux) and continue the tip motion to allow the tip to press against and heat the part(s); and 4) dwell and then release the solder iron.
SUMMARY OF THE INVENTION
The present invention is designed to provide a low cost, low maintenance, general-purpose machine, which also eliminates the problems involved with other systems.
The cycle sequence of the solder iron tip motion, tip temperatures, tip velocity, solder wire feed rates, and solder wire feed pressures are precisely controlled for each application with considerations including the part size, solder wire size, cycle speed, dwell time between parts, factory temperature variations, line voltage fluctuations, and material variations. These adjustments can only be optimized by an experienced person with access to proper tools and equipment.
One example according to the teachings of this invention provides a non-adjustable machine that is preset at the solder machine factory for a specific part.
A second example according to the teachings of this invention provides an automatic spot solder machine with adjustable controls limited to the solder wire feed length and cycle speed.
A third example according to the teachings of the present invention includes means to heat the tip from 500° F. to 700° F. within 0.75 seconds or less, including means to cool the tip from 700° F. to 500° F. within 1.5 seconds or less.
The rapid cooling and heating of the solder iron tip are required to maintain a reasonable high production rate, which also provide many variations of the basic cycle sequence. Also, the cool tip prevents the tip surface from oxiding and losing its solder coating when not in use. However, if some area of the tip loses its coating, a low temperature melting of the solder and flux allows the tip to become re-coated with solder. This eliminates the need for a tip “cleaning” cycle.
An exemplary cycle utilizing the teachings of the present invention can be: 1) the solder iron tip is normally at a temperature of 300° F. to 500° F. when idle; 2) feed the solder wire out to position the front section between the tip and part(s); 3) simultaneously lower the tip onto the solder wire and heat the tip to a temperature of 400° F. to 600° F.; 4) melt the solder wire and flux at this low temperature, which reduces or eliminates splatter of flux and solder; 5) increase the tip temperature to 600° F. to 1200° F., for a rapid saturation of solder into the part(s); and 6) return the tip to its original position and simultaneously allow the tip to cool to a temperature of 300° F. to 500° F. in time for the next cycle.
Another exemplary cycle utilizing the teachings of the present invention can be: 1) the solder iron tip is normally at a temperature of 300° F. to 500° F. when idle; 2) lower the tip onto the part(s) and simultaneously heat the tip to a temperature of 500° F. to 700° F.; 3) feed the solder wire/flux into a hole on the side of the solder tip, where a connecting hole on the bottom surface of the tip allows the molten solder and flux to exit the tip and onto the part(s) (see FIG.
3
); 4) increase the tip temperature to 600° F. to 1200° F., for a rapid saturation of solder into the part(s); and 5) return the tip to its original position and simultaneously allow the tip to cool to a temperature of 300° F. to 500° F. in time for the next cycle.
A fourth example according to the teachings of the present invention includes a solder iron tip with a cross hole for feeding the solder wire into the hole. This allows the solder/flux to melt within the solder tip, which eliminates all splatter of flux and solder. Exiting the molten solder/flux through a hole at the bottom of the tip places the solder/flux exactly where the part(s) are located. (See FIG.
3
).
The objectives in feeding the wire through the tip include: 1) prevent splatter of flux and solder; 2) deposit the solder/flux precisely; 3) reduce the decomposition of the flux by reducing the area and contact time of the flux on the hot solder tip, which also improves the solder saturation into the parts and assists in maintaining a coated solder tip; and 4) create a high-pressure extrusion of the molten solder/flux out of the solder tip, onto the part(s).
Many previous attempts by others and this inventor to provide a solder wire feed through a hole in the solder tip were unsuccessful. Large diameter solder/flux wire over 0.125 inches, which is seldom used in high production, is relatively easy to process by this method. Smaller diameters are possible only with a precise design and control of many inter-related variables.
These variables are: temperature of the solder tip; diameter and feed rate of the solder wire; diameter, length, and thermal conductivity of the solder tip; size and length of the entrance hole; cycle speed; and timing. It is desired to feed the solder wire through the hole without any blowback. The entrance hole may be larger or smaller than the solder wire diameter. If the hole is smaller than the wire, the wire may be pushed in with a high force and high speed, which shaves or melts the outside surface of the wire. If the tip temperature is hot enough, the wire surface can be melted at any reasonable speed. If the feed rate is too slow for any given temperature, the outside surface of the wire
Dunn Tom
McHenry Kevin L.
Pauley Petersen & Erickson
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