Electric heating – Metal heating – By arc
Reexamination Certificate
1999-12-01
2001-09-04
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C228S180220, C228S234100
Reexamination Certificate
active
06284998
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates generally to laser soldering, and more particularly to a method for laser soldering electronic components to a three dimensional circuit board substrate.
2. Disclosure Information
Electronic components are typically connected to circuit boards using either conventional reflow or wave soldering. An alternative and heretofore less widely used method is laser soldering, illustrated in FIG.
1
. Laser soldering is often preferred over conventional reflow processing when the substrate is made of a material that is more temperature-sensitive than conventional laminated FR4 glass-epoxy, such as a low melting point polymer or a thin flex circuit.
In conventional laser soldering, an electronic component
10
is placed atop a dielectric substrate
14
with the component terminations
12
resting atop solder pasted mounting pads
24
, and a laser beam
70
from a YAG, Nd:YAG, diode, or other laser
50
is directed at one or more mounting pads
24
and/or solder depositions
26
, in order to melt and reflow the solder paste
26
to form solder -joints.
However, conventional laser soldering has always been limited to use with those components whose terminations remain visible after the component is mounted atop its respective solder-pasted mounting pads. These include components having conventional J-leads, gull-wing leads, or end terminations (such as in leadless chip components or LCCs) arranged about one or more sides of the component body. However, laser soldering has heretofore not been utilized on components whose terminations are arranged on an underside surface of the component, such as ball grid arrays (BGAs), pin grid arrays (PGAs), and the like. This is because the standard practice in laser soldering is to direct the laser beam
70
in a line-of-sight manner from a position above the substrate top surface
16
on which the component
10
is mounted, thus precluding its use on components whose terminations are “hidden” beneath the underside of the component when the component is mounted on its solder-pasted mounting pads. Thus, when a circuit board/substrate contains, for instance, J-lead, gull-wing, and BGA/PGA components and it is desired to use laser soldering, typical practice in this case would be to laser solder only the J-lead and gull-wing components, and to separately solder the BGAs/PGAs using a separate reflow process either before or after the laser soldering process. This requirement of a separate reflow step presents a significant drawback to the prospect of using laser soldering, not only because it requires the use of two separate soldering steps (i.e., reflow and laser soldering), but also because it typically requires the use of two separate solder pastes (i.e., one having a first melting point for the J-lead/gull-wing components, and another having a different melting point for the BGA/PGA components).
Because space is limited, housings for automotive vehicle components are continuously being reduced. Commonly, housings have several circuit boards contained therein. The multiple circuit boards take a substantial amount of space. However, further reduction in space of electrical components is desirable.
It also would be desirable to provide a method for using laser soldering with both (1) BGAs, PGAs, and other components having one or more terminations on an underside surface or a an inside surface thereof, and (2) J-lead, gull-wing, endterminated, and other such components.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior art approaches by providing a method for laser soldering a three dimensional component having an interior portion, comprising the steps of:
providing an electronic component having at least two terminations thereon; a substantially flat dielectric substrate having a first surface on a first side thereof, a second surface on a second side thereof, and at least two mounting pads arranged on the first surface in matched relation with the terminations of the electronic component; and a diode laser;
depositing solder paste atop the mounting pads;
placing the electronic component atop the substrate such that each termination rests generally atop its respective mounting pad;
forming a three dimensional structure from said substrate; and
after the step of forming a three-dimensional structure, directing laser energy from the diode laser to at least one of the mounting pads from the second side of the substrate for a predetermined time, such that the solder paste atop the at least one of the mounting pads is melted.
It is an object and advantage that the method of the present invention may be used to laser solder components having terminations on an inside surface of a three dimensional component.
Another advantage of the invention is that a housing with the electrical components therein may be formed by the circuit substrate. Thus, the size of the housing may be reduced.
Another advantage is that the method of the present invention may laser solder such components without requiring modification of the component, terminations, mounting pads, solder paste depositions, substrate, or any other aspect of the electronic circuit assembly.
Yet another advantage is that the method of the present invention may be used not only for surface mount components having terminations on an underside surface thereof, but also for any other type of surface mount or plated through-hole component.
These and other advantages, features and objects of the invention will become apparent from the drawings, detailed description and claims which follow.
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Beckett et al., “The application of semiconductor diode lasers to the soldering of elecgtronic components, ” Optical and Quantum Electronics, vol. 27, No. 12, pp. 1303-1311, Dec. 1995.
Coyner Rexanne M.
Glovatsky Andrew Zachary
Lemecha Myron
Meyer Bernard Allen
Shi Zhong-You (Joe)
Heinrich Samuel M.
Kajander John
Visteon Global Technologies Inc.
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