An improvement in a reflow soldering apparatus for bonding a connector element such as flexible circuitry or a pin type input/output (I/O) connector to a printed circuit board (PCB) is disclosed wherein a fixture tray included in the apparatus automatically aligns or self levels itself with the heating bars, or thermodes, of the apparatus. The fixture tray includes a body for supporting the connector/PCB assembly and cylindrical rods extending from the body. The rods are rotatably supported in corresponding grooves on the surface of the fixture tray table. As a thermode is pressed onto the connector/PCB assembly, the fixture tray rotates about its axis of rotation until the work area is aligned with the thermode. In a sandwich type soldering application including a pair of thermodes for simultaneously soldering opposite sides of a connector/PCB assembly, the fixture tray rests on an upper plate of a tray table supported by resilient means such as springs. Pressing an upper thermode onto the upper work surface of the connector/PCB assembly causes the work surface to rotate into alignment with the thermodes, and further causes the upper plate to descend until the bottom work surface of the connector/PCB assembly contacts the lower thermode prior to initiation of a reflow soldering cycle.

FIELD OF THE INVENTION 
The present invention relates generally to tool fixtures and soldering 
systems, and more particularly to a self-leveling, self-aligning fixture 
for precision reflow soldering applications. 
BACKGROUND 
There are many reflow soldering applications that require precise alignment 
and coplanarity between components for proper electrical and mechanical 
bonding. One of the final steps in the production of a printed circuit 
board (PCB) such as a PCMCIA card, for example, is the reflow soldering of 
the PCB to an input/output connector (I/O connector). A typical I/O 
connector may be single or double-sided and has a plurality of fragile 
leads or pins, each of which corresponds to a respective connector trace 
at the edge of a PCB card. To reflow solder these components together, a 
small amount of flux is placed on the connector traces on the PCB to form 
solder pads. The I/O connector is then placed or slipped on the end of the 
PCB to form a temporary connector/PCB assembly and the two components are 
then reflow soldered to create a finished assembly. 
Reflow soldering of connector/PCB assemblies has been accomplished by many 
different methods. One common method for double-sided connectors involves 
sandwiching the assembly between two hot bars, or thermodes, using 
pressure and heat to reflow solder the leads to the PCB. Alignment of the 
pins on the I/O connector with the corresponding solder pads on the PCB 
and coplanarity between the I/O connector and PCB are critical to ensure 
good mechanical and electrical coupling at every connector trace and 
compliance with industry standard specifications. The specifications for 
personal computers, laptops and other electronic products, for example, 
require that the edges of the connector and PCB be parallel and within a 
certain distance of one another in order for the assembly to be 
mechanically packaged in the final product. 
Such specifications, however, are sometimes difficult to achieve because 
PCBs often become warped by heat and mechanical forces the board 
experiences during processing. This creates problems during reflow 
soldering since warpage of the board can prevent proper alignment of the 
thermode contact surface with the connector/PCB assembly. Misalignment can 
result in an uneven pressure profile at the surface to be soldered, or 
work surface, creating either too much pressure at some soldering sites 
and/or too little pressure at other sites. If the pressure exerted by the 
thermodes is too large, the leads may be squeezed toward each other and 
solder may flow over multiple leads, causing a short circuit. Conversely, 
if the pressure is too small in certain areas, the resulting bonds may be 
too weak, resulting in an open circuit or even mechanical failure. 
One solution known in the art to prevent misalignment of the connector/PCB 
assembly with the thermodes has been to place a pivot at the top of the 
thermode head. However, undesirable skidding can occur in this arrangement 
if one edge of the thermode contacting surface initially contacts the work 
area between two I/O connector pins, consequently engaging a lead and 
pushing the connector out of alignment with the PCB during its rotation. 
Such skidding can cause damage to the connector leads, misalignment 
problems including offset between the leads and corresponding connector 
traces, and movement of the connector out of the plane of the PCB. 
Another solution aimed at addressing these skidding problems has been to 
provide thermodes connected to two leaf spring flexures, usually thin 
blades of stainless steel. In this thermode head, the thermode pivots 
around a point at the center of the contact surface of the thermode. While 
this may reduce skidding, such devices are somewhat complicated and 
expensive to manufacture. In addition, the resilience of the material used 
in the leaf spring flexures can be affected by heat during the reflow 
cycle, which over time can reduce the reliability and repeatability of the 
reflow soldering process. 
In view of the deficiencies in the known processes, those skilled in the 
art would desire an improved system for reflow soldering electrical 
components, which can accommodate for any misalignment or non-coplanarity 
between the connector and connector/PCB assembly and allow for leveling of 
the heating element without skidding. 
SUMMARY OF THE INVENTION 
The present invention provides a novel self-aligning fixture having a 
fixture tray and table for reflow soldering electrical components such as 
a printed circuit board (PCB) and a corresponding input/output (I/O) 
connector. A connector/PCB assembly is placed on a fixture tray in the 
self-aligning fixture which rotates into place to correctly align the work 
surface of the connector/PCB assembly with the thermode contacting surface 
prior to reflow soldering. The fixture tray includes a body and first and 
second cylindrical rods extending from opposite sides of the body. The 
fixture tray is removably mounted in an upper plate of a tray table having 
a window adapted to rotatably support the tray and first and second 
grooves adapted to accommodate the fixture tray rods. The rods allow the 
fixture tray to self-level and rotate into alignment when the thermode 
contacting surface is pressed onto the connector/PCB assembly. 
In the case of applications requiring simultaneous reflow soldering of 
opposite sides of a component such as a double-sided I/O connector to a 
PCB, bearing shafts are attached to the upper plate of the tray table and 
are resiliently mounted in corresponding shaft housings extending through 
a lower plate of the table. This allows vertical motion of the upper plate 
with respect to the lower plate and provides clearance for the fixture 
tray to rotate and self-level with the upper thermode contacting surface 
prior to contact between the bottom work surface of the connector/PCB 
assembly with the lower thermode contacting surface. 
In operation, as the upper thermode is lowered and contacts the top work 
surface on the connector/PCB assembly, the fixture tray rotates to bring 
the work surface into full contact with the thermode contacting surface. 
The upper thermode continues to press into the assembly, pressing the 
upper plate of the tray table downward until the bottom work surface of 
the connector/PCB assembly makes contact with the lower thermode 
contacting surface and the proper pressure between the connector/PCB 
assembly and the thermodes is attained. The thermodes are then heated and 
the PCB is reflow soldered to the connector.

DETAILED DESCRIPTION 
Referring to FIG. 1A, a preferred embodiment of a reflow soldering 
self-aligning fixture according to the invention is used to reflow solder 
electrical components such as a PCMCIA printed circuit board (PCB) 10 with 
substrate 11 to a standard 68-pin double-sided input/output connector (I/O 
connector) 12. The I/O connector 12 has two rows of pins 8 (FIG. 1B) which 
correspond to previously fluxed connector traces on the top and bottom of 
the PCB. The connector/PCB assembly 14, shown in FIG. 1C and FIG. 1D, is 
formed by slipping the PCB into the space between the two rows of 
connector pins. The surfaces to be soldered are located at the junction 
between the I/O connector and the PCB and include a top work surface 5 and 
a bottom work surface 7. 
The connector/PCB assembly is then placed on the fixture tray 16 shown in 
FIG. 2. The tray includes a body 18 including a component assembly 
supporting surface 19 and front and rear raised walls 21, 23 and an axis 
of rotation 3. In the presently preferred embodiment, the assembly 
supporting surface 19 is a substantially flat plate having custom designed 
apertures 17, 20 designed to support the I/O connector and the PCB. 
Locating pins 22 (shown exaggerated in FIG. 2) provided on the tray body 
18 fit into corresponding locating holes 9 (FIG. 1A) on the PCB to ensure 
proper alignment of the connector/PCB assembly on the tray. The fixture 
plate can be designed in numerous ways to accommodate different types of 
electrical components and assemblies for a wide range of applications. 
Referring to FIG. 2 and FIG. 3, the fixture tray further includes a front 
rod 24 and rear rod 26 extending from the respective walls of the tray 
body. In a preferred embodiment of the fixture, the axial centers 25, 27 
of the rods are aligned with the axis of rotation 3 of the tray and are 
located above the assembly supporting surface substantially in the PCB 
substrate center plane 90 (FIG. 10). The center plane is located 
equidistant between the planes of the top surface 95 and bottom surface 97 
of the PCB substrate. 
The fixture tray is removably and rotatably mounted on a table including a 
rectangular upper plate 28 (FIG. 4) and U-shaped lower plate 42 (FIG. 5). 
As shown in FIG. 8, the fixture tray is mounted to the table by placing 
the tray in the window 32 and the front and rear rods 24, 26 in 
corresponding V-shaped grooves 36, 38 provided on the upper (top) surface 
30 of the upper plate. In a preferred embodiment, the tray is designed to 
sit in the window 32 of the upper plate with the rods resting in the 
grooves, thereby allowing the tray to pivot around the center of the two 
rods. 
For mounting the upper plate on the lower plate, the upper plate further 
includes a pair of bearing shafts 40. The bearing shafts 40 slide into 
bearing housings 46 extending through the lower plate. As shown in FIG. 6, 
helical return springs 102 are placed on the bearing shafts to resiliently 
suspend the upper plate over the lower plate and to allow the upper plate 
to move relative to the lower plate. 
A conventional sandwich type reflow soldering system includes upper and 
lower thermodes 50 and 54 attached to upper and lower reflow soldering 
heads 70 and 72 (FIGS. 8-9). For use with the self-aligning fixture 
according to the present invention, the lower thermode 50 is positioned 
within a recess in the lower plate 42, as shown in FIG. 7. The lower plate 
can be adjustably positioned along the X and Y-axes by means of a 
positioning slide assembly 47 having substantially similar micrometer 
adjustment knobs for the X-axis 48 and the Y-axis 49. As shown in FIG. 8, 
the upper thermode 54 is attached to an adjustable thermode press (not 
shown) for Z-axis movement relative to the connector/PCB assembly. A 
suitable reflow soldering system adapted for use with the present 
invention is disclosed in applicant's provisional patent application Ser. 
No. 60/004,001, filed Sep. 20, 1995, the contents of which are hereby 
incorporated by reference. 
In operation, reflow soldering a PCB to an I/O connector is accomplished by 
first placing the connector/PCB assembly 14 on the fixture tray body 18 
using the locating pins 22 to correctly align the connector/PCB assembly. 
The fixture tray 16 is then placed upon and positioned in the upper plate 
28 of the fixture table 100 such that the front end 21 of the fixture tray 
body is flush with the front wall (not shown) of the window. In one 
embodiment, this is accomplished by providing push pins or any other 
suitable biasing mechanism positioned adjacent the rear wall 33 of the 
window to press or bias the fixture tray into the front wall of the 
window. 
Prior to the initial use of the invention with a particular connector/PCB 
assembly, the contact surface 82 of lower thermode is aligned with the 
bottom work surface of the connector/PCB assembly by using the micrometer 
adjustments 48, 49 on the X-Y axes positioning slide assembly 47. Then, 
the contacting surface 80 of the upper thermode 54 is aligned directly 
over the contacting surface 82 of the lower thermode, as shown in FIG. 9. 
After the initial set up, the upper thermode is lowered until it makes 
contact with the top surface of the connector/PCB assembly. The downward 
motion of the thermode presses the thermode contacting surface onto the 
top work surface 15 of the connector/PCB assembly which causes the fixture 
tray to rotate or pivot about its axis of rotation, thereby aligning the 
top work surface of the connector/PCB assembly with the upper thermode 
contacting surface. As the upper thermode continues its downward motion 
causing the return springs 102 to compress, the upper assembly, tray and 
plate descend until the lower thermode contacting surface contacts the 
bottom of the connector/PCB junction. The thermode press continues to 
force the upper thermode down until a conventional sensing mechanism in 
the fixture detects a preset pressure between the thermodes and the 
connector/PCB junction. When the movement stops upon reaching a desired 
pressure, heat is applied to reflow solder the connector leads to the PCB 
to produce a finished assembly. 
As will be appreciated by those skilled in the art, the self-aligning 
fixture according to the present invention ensures flatness through 
self-leveling between the connector/PCB assembly and thermode contacting 
surfaces. In addition, it ensures repeatability of the final position of 
the connector. This is accomplished by making the connector/PCB assembly 
align to the thermode contacting surfaces. 
While a preferred embodiment of the invention has been illustrated and 
described, it should be understood that variations will be apparent to 
those skilled in the art. Any suitable means may be used, for example, to 
rotatably mount the fixture tray to the table, such as a ball and socket 
assembly, bearings, or other suitable joint. Similarly, any suitable means 
may be used to resiliently mount the upper table to the lower table. In 
some applications, a separate upper and lower table may not be necessary. 
In addition to PCMCIA applications, the invention could be used to reflow 
solder a variety of different components such as, for example, circuit 
components or flexible cable to a PCB. The invention could also be 
modified for isotropic and anisotropic tack and bond processes, for 
applications requiring only one thermode, or for applications requiring 
more than one thermode at different sites on the same side of the PCB. 
Also, since the fixture tray of the invention is removable, the production 
throughput could be increased by loading connector/PCB assemblies into 
multiple fixture trays offline. Furthermore, additional structures can be 
utilized for pulsed heating and forced air cooling of the thermodes as is 
well known in the art. Accordingly, the invention is not to be limited to 
the specific embodiments illustrated and described, but should be 
determined by reference to the following claims.