Robotic Tinning Station for Axial Lead Electronic Components

This invention relates to the tinning of leads on electronic components and, more particularly, to a system for automatically tinning the leads of axial lead electronic components.

In order to improve the solderability of the leads of electronic components, it is desirable to deposit a thin layer of solder on the component leads prior to the insertion of the components in an electronic circuit. The process of forming this thin layer of solder is generally referred to as tinning and is typically manually performed by an operator who first dips the component leads into solder flux and then dips the leads into a molten pool of solder. This process is not only tedious and time-consuming but it also presents certain safety hazards by exposing the operator to solder flux and molten solder. It is therefore desirable to devise an automated tinning system which would enhance operator safety while reducing the time required to complete the process for a given number of components.

A tinning station constructed in accordance with the present invention is particularly adapted to tinning the leads of axial lead electronic components and includes a presentation system for arranging a plurality of axial lead components in an elevated linear array. Each of the components includes a body with an axis and a pair of leads extending from opposite sides of the body along the axis. In the array, axes of adjacent components lie generally parallel to each other. A pair of grippers, each including a bar having a length at least as long as the linear array of components, are provided to grasp the array. The gripper bars are generally parallel to each other and may be moved toward and away from each other by an actuator which is mounted on a robotic arm. A longitudinal slot in each gripper bar accepts the component leads and allows the grippers to close on the ends of the component bodies. Devices are provided which contain a pool of solder flux and a pool of solder. The robotic arm is programmed to maneuver and actuate the grippers such that they pick up the component array from the presentation block, dip the leads of the array in the solder flux and subsequently dip the leads of the array in the molten solder. The thickness of the gripper bars can be varied to vary the length of an untinned portion of the component leads adjacent to the component bodies.

When using a tinning station in accordance with the present invention, an operator need only load the axial lead components onto a presentation block, or into a feed hopper, and can thereby maintain a safe distance from the flux and molten solder.

FIG. 1 is a schematic representation of a tinning station constructed in accordance with one embodiment of the present invention;

FIGS. 2A, 2B and 2C are top, side and end views, respectively, of the presentation block used in the system of FIG. 1;

FIGS. 3A and 3B are top and side views, respectively, of one of the grippers used in the tinning system of FIG. 1;

FIGS. 4A and 4B are side and end views, partially in section, of an alternative embodiment of the solder containing device of the system of FIG. 1;

FIGS. 5A, 5B and 5C are end, side and top views, respectively, of the release bar of the station of FIG. 1; and

FIGS. 6 and 7 are schematic representations of portions of an alternative presentation system.

Referring to the drawings, FIG. 1 is a schematic representation of a tinning station constructed in accordance with one embodiment of the present invention. This station includes a presentation system in the form of a block 10 for arranging a plurality of axial lead electronic components 12 in a linear array 14. Each of the components includes a body 16 having an axis and a pair of leads 18 and 20 which extend from opposite sides of the body along the axis. When arranged in the linear array, the axes of adjacent components lie generally parallel to each other. A pair of grippers 22 and 24 are mounted on an actuator 26 which is in turn mounted on a robotic arm 28. The grippers include bars 30 and 32 which lie generally parallel to each other and can be moved toward or away from each other by the actuator 26. A programmable controller 34 is used to control the operation of the robotic arm and actuator.

A flux pot 36 contains a pool of liquid solder flux 38 having a generally horizontal surface. A solder pot 40 contains a pool of molten solder 42 also having a generally horizontal surface. A release bar 44 is provided with a pair of spaced tines 46 and 48 which serve to dislodge components from the grippers following the tinning operation thereby causing the components to fall into cup 50.

To perform the tinning function, an operator first places several axial lead components in the presentation block 10. The robotic arm then slides the grippers along the array of components and the actuator closes the gripper bars to secure the component array between the grippers. The grippers are moved inward to secure the component bodies between the grippers. In one embodiment of the invention, up to seven components can be processed at one time. Then the robotic arm moves the grasped array of components to the vicinity of the solder pot. The array is rotated 90.degree. and the leads on one side of the array are dipped into and out of the flux. The array is then flipped and the leads on the other side of the array are dipped into and out of the flux. Next, the array is transported to a heated solder pot and the leads on one side of the array are dipped into the molten solder (at 500.degree..+-.20.degree. F.) for approximately four seconds. The array is slowly lifted vertically out of the molten solder and rotated 180.degree.. The other leads of the array are subsequently dipped into the molten solder for four seconds. The robotic arm slowly lifts these component leads vertically out of the molten solder and transports the component array to an unloading station. Here the grippers pass under a pair of tines on the release bar 44 and, with the grippers open, the grippers are pulled vertically between the tines and the parts are unloaded into cup 50. Then the robotic arm moves the grippers to the presentation block to pick up the next array of axial lead components.

The robotic arm, programmable controller and actuator may be any available robotic arm system which is capable of moving and operating the grippers in the necessary manner. For example, a tinning station constructed in accordance with the present invention has used an Alpha II, robotic arm, available from Microbot, Inc., Mountain View, Calif.

FIGS. 2A, 2B and 2C are top, side and end views of the presentation block 10 in the system of FIG. 1. This block includes a pair of generally vertical sides 52 and 54 having sloping top surfaces 56 and 58. A plurality of notches 60 are cut into these top surfaces and are positioned to receive the axial leads 18 and 20 which extend from the bodies 16 of the axial lead components 12. Corresponding notches are cut in surfaces 56 and 58 and the notches are spaced to prevent contact between the bodies of adjacent components.

FIGS. 3A and 3B are top and side views of one of the grippers used in the system of FIG. 1. Since the grippers of FIG. 1 are identical, only one is illustrated in FIGS. 3A and 3B. That gripper is an L-shaped piece that includes a first end 62 which is attached to the robotic arm actuator and a bar 30 having a length which is at least as long as the length of the array of electronic components to be tinned. The bar 30 includes a slot 64 which receives the leads of the axial lead components. A layer of resilient material 66 may be attached to one side of the bar 30 to prevent slippage of the axial lead components when they are clamped between grippers. Two layers of masking tape have been shown to function adequately as this resilient layer, for a limited time. The grippers may be constructed from a material which does not readily adhere to solder, such as stainless steel or aluminum.

FIGS. 4A and 4B illustrate an alternative soldering device which may be used in the system of FIG. 1. This device is a solder fountain wherein molten solder 68 flows as illustrated by the arrows, up a central spout between walls 70 and 72 and back down between walls 74 and 76. in FIGS. 4A and 4B, the grippers 22 and 24 were inserted in a direction perpendicular to the component leads and positioned adjacent to opposite ends of the component body 16 such that the component leads 18 and 20 extend through the slots in the grippers and the grippers are clamped against opposite sides of the bodies. In this clamping arrangement, the thickness 78 of the grippers is used to define an untinned portion of the component leads adjacent to the component bodies. In certain applications, specifications require that the tinned portion of the leads must be spaced from the component body by a particular distance, for example, one-sixteenth of an inch. In these instances, grippers having bars with the appropriate thickness can be fabricated to prevent tinning along the desired length of the leads which lies adjacent to the component bodies. Of course, the solder fountain (or solder pot in FIG. 1) must be high enough to provide clearance for the actuator 26, thereby permitting the positioning of the bottom gripper adjacent to the top of the molten solder.

FIGS. 5A, 5B and 5C represent end, side and top views of the release fixture of the station of FIG. 1. This fixture includes a pair of tines 46 and 48 which are spaced far enough apart for the grippers to pass vertically between them. For the case where the gripper hold the sides of the components as illustrated in FIG. 5B, the distance between the tines should be larger than the length of the bodies of the components so that only the component leads touch the tines as the grippers are pulled vertically between them. The base 80 of the release fixture is configured to accept the cup 50.

FIGS. 6 and 7 are schematic representations of portions of an alternative component presentation system to be used in the present invention. In this presentation system, components to be tinned are loaded into a zig-zag hopper 82 which is positioned adjacent to a conveyor system 84. The conveyor system includes a pair of belts 86 and 88 which are mounted on a pair of pulleys 90 and 92. A star wheel 94 is mechanically coupled to the conveyor to turn as the conveyor belts move thereby causing pivot arm 96 to pivot about pivot pin 98 causing reciprocal movement of actuating arm 100. A spring 102 maintains contact between the pivot arm and the star wheel. Reciprocal movement of the actuating arm 100 actuates the component deposition mechanism within the commercially available zig-zag feed hopper thereby depositing components on the conveyor belts 86 and 88. These components are positioned generally parallel to each other as illustrated in FIG. 7. As the components reach the end of the conveyor, a sensor (such as an electric eye 104) detects the presence of these components and sends a signal to the conveyor control 106 thereby turning off the conveyor. Then the robotic grippers 22 and 24 extend between the conveyor belts and close onto a plurality of components to be tinned.

This presentation system eliminates the need for an operator to manually load a presentation block each time the robot arm is cycled. Once the robot arm removes a preselected number of components from the conveyor, the sensor indicates that components are not present near the end of the conveyor and the conveyor control is signalled to restart the conveyor thereby causing additional components to be deposited on the conveyor belts. It should be noted that the distance D between conveyor belts 86 and 88 must be sufficient to accommodate not only the component bodies 16 but also the grippers 22 and 24 with sufficient additional clearance to permit the grippers to be inserted on opposite sides of the component bodies.

Although the present invention has been described in terms of what is at present believed to be its preferred embodiment, it will be apparent to those skilled in the art that various changes may be made to the system without departing from the scope of the invention. It is therefore intended that the appended claims cover such changes.