Solder terminal

A solder terminal includes a clip adapted to be positioned on one edge of a substrate for forming soldered electrical connections with substrate pads. One end of the clip extends away from the substrate for making an electrical connection with a circuit component.

FIELD OF THE INVENTION 
The invention relates to solder terminals, particularly solder clips for 
forming solder connections with contact pads on the edges of substrates. 
DESCRIPTION OF THE PRIOR ART 
Conventional solder terminals include clips for mounting on the edges of 
substrates with the interior surfaces of the clips engaging pads on the 
substrate. The clips carry masses of solder located remote from the 
clip-substrate contact. Electrical connections are formed between the 
clips and the pads on the substrate by heating and reflow soldering. This 
soldering operation requires melting of the solder mass and flowing of the 
molten solder to the pads. Improper flowing of the solder to the joints 
risk improper soldered electrical connections between the clip and the 
pads. Specialized tooling and production techniques are required for 
physically securing solder masses to the terminals. 
One clip-type solder terminal provides a solder mass bonded to the surfaces 
of the clip which are bent down laterally to either side of central 
contact ridges extending along the clips. During reflow soldering the 
solder located away from the contact ridges melts and is drawn into solder 
fillets extending to either side of the ridges and forming connections 
between the clip and the contact pads. While this type of solder terminal 
does work, the manufacture is difficult due to the necessity of bending 
the contact arms down to either side of the ridges. The ridge-pad contacts 
between the clips and the substrate pads are relatively unstable making it 
difficult to maintain solder individual clips in place on the substrate 
prior to soldering. 
SUMMARY OF THE INVENTION 
The present solder terminal is formed from a strip of flat metal stock 
having a reflow adhered solder overlay in the clip-portion. This overlay 
is coined down onto the flat strip to a uniform thickness of about 0.0005 
inch. Coining of the strip extrudes two large volume solder bodies 
laterally beyond the strip edges. During forming of the clip these bodies 
remain secured to the strip through the very thin solder layer. 
Following coining, a clip is formed by single-curvature bending of the 
strip. One clip arm includes a flat large area contact surface and the 
other clip arm includes a contact ridge extending laterally across the 
strip. The solder masses extend around the U-shaped edges of the clip. The 
solder terminals are inexpensively and rapidly mass produced by a 
relatively simple stamping, coining and single curvature forming 
operations. 
The solder terminal is mounted on a substrate by moving the clip over the 
substrate edge so that the contact surface and ridge rest on opposed 
contact pads. The substrate has a thickness greater than the spacing 
between the surfaces so that the flexible bridge joining the clip arms is 
stressed and biases the contact surface and ridge against the pads and 
holds the thin solder layers flush on the flat pads. 
The mounted clip is electrically connected to the pads by heating and 
reflow soldering. Heating and melting of the thin solder layers confined 
between the clip arms and pads forms integral solder connections between 
the arms and the contact surfaces and pads. These connections are formed 
by the solder in the thin layer. The large volume solder reservoirs 
located to the sides of the clip are melted and are drawn by capillary 
action into the corners surrounding the contact surface and ridge to form 
large volume strong solder fillets surrounding the two contact joints. The 
fillets form the electrical and physical connections between the clip and 
the contact pads. 
Other objects and features of the invention will become apparent as the 
description proceeds, especially when taken in conjunction with the 
accompanying drawings illustrating the invention, of which there are 2 
sheets and one embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a flat solder terminal preform 10 including elongate carrier 
strip 12 with regularly spaced pilot holes 14 formed along the length of 
the strip. A plurality of spaced flat metal terminal strips 16 extend to 
one side of the carrier strip. Each terminal strip includes a flat solder 
overlay 18 integrally bonded to the strip, preferably by reflow soldering. 
The overlays 18 are located centrally on strips 16. The preform 10 is 
preferably stamp formed from a metal strip with a continuous solder 
overlay extending down the middle of strips 16 by blanking away the 
sections of the strip and solder overlay between adjacent terminal strips 
16. 
The strips 16 may have a thickness of about 0.008 inch and a width of about 
0.02 inch. The solder overlay 18 may have a thickness of about 0.004 inch 
and projects above the strips 16 as shown in FIG. 2. 
Following manufacture of preform 10, the solder overlays 18 are coined to 
flatten the solder above the strip 16 and extrude the solder laterally 
beyond the edges of the strips. The extruded solder forms relatively thick 
and large volume solder masses 20 extending along the edges of each 
terminal strip 16. The working face of the coining tool is parallel to the 
flat top of the strip 16 and is lowered through a sufficient distance to 
reduce the thickness of the solder and form a thin solder layer 22 
directly overlying the strip having a thickness of about 0.0005 inch. This 
thin layer is integrally bonded to the strip. The flat outer surface of 
layer 22 continues over the solder bodies 20 as illustrated in FIG. 4. The 
coining operation flows or extrudes the major portion of the overlay 
solder into the solder bodies 20 located outside of the strips 16. 
Following coining of the solder overlays 18, the flat terminal strips 16 
are bent along their length to the configuration shown in FIGS. 5 and 6. 
Easily formed single curvature bends are made along the strips to form 
solder clip terminals 24 each having a free contact end 26 and a substrate 
clip 28 located medially along the length of the terminal. The coined 
solder layer 22 extends around the interior of clip 28 and along each clip 
arm 30 and 32 and the bridge 34 joining the ends of the arms. Arm 30 
includes an inwardly facing contact ridge 36 extending across the width of 
the arm. Arm 32 includes a flat contact surface 38 facing ridge 36. 
During forming of the solder terminals 24, the straight solder bodies 20 of 
preform 10 remain joined to the solder layer 22 and are bent around the 
edges of clip 28 as shown in FIGS. 5 and 7 to form generally U-shaped 
solder reservoirs 40 extending around each edge of the clip along the 
edges of the arms and bridge. As shown in FIG. 7, the reservoirs 40 
include portions 42 and 44 having a greater thickness than the adjacent 
clip arms 30 and 32 and projecting distance outwardly beyond the arms. The 
thin solder layer 22 and reservoirs 40 extend completely around the 
interior of the clip. The clip lead in portions 44 and 46 open into an 
interior clip recess 48 located between the flat wall 38 of clip arm 32 
and the ridge 36 of clip arm 30. 
Solder clip terminals 24 are mounted on substrate 50 as shown in FIG. 8. 
The edge of the substrate is piloted between the lead-in portions 44 and 
46 and the clip is then pushed on the board to position arms 30 and 32 on 
a pair of contact pads 52 and 54 on the substrate. The width of the 
substrate and pads is slightly greater than the minimum spacing between 
clip arms in the terminal 24 so that the clip is stressed and the arms are 
held tightly on the pads. Arms 30 and 32 are separated from the pads by 
the thin solder layer 22. The clip is oriented on the board by flush 
engagement between the flat pad 54 and the flat surface 38 of arm 32. The 
contact ridge 36 of arm 30 rests flush of pad 52. 
With the solder terminal mounted on the substrate as shown in FIG. 8 
permanent electrical solder connections are established between the arms 
and the pads by heating and reflow soldering. Heating the solder clip 
melts the thin solder layer 22 between the arms and the contact pads to 
form, when cooled, a thin solder layer 56 extending across the full width 
of each arm and integrally bonding overlying arm surfaces to the pads 52 
and 54. This bonding solder layer has a thickness of about 0.0005 inch. 
The solder reservoirs 40 located along each edge of the clip are melted 
during reflow soldering and flow to strong solder fillets 58 forming 
integral solder connections between the edges of the clips and the edges 
of the contact pads. These solder fillets are drawn by capillary action 
across the width of the arms where the arms extend away from the pads to 
form a continuous solder fillet at each arm completely surrounding the 
solder bond layer 56. 
Following reflow soldering of the terminals 24 to substrate 50 the strip 12 
is broken away from the individual terminals to electrically isolate the 
individual terminals. Contacts 26 form electrical connections between the 
terminal pads and other circuit elements. Terminal 24 may include other 
types of contacts for forming electrical connections with circuit 
elements. For instance, the ends of the terminal may be left straight and 
soldered in contact holes formed through a support member or may be joined 
to another circuit element through a connector block. 
During heating and reflow soldering of the clip to substrate 50 as shown in 
FIG. 9, the thin layers 22 melt and form reflowed soldered connections 
integrally joining the overlying clip arms to the underlying contact pads 
without appreciable migration of additional solder into the interface 
between the arms and pads. The solder reservoirs 42 and 44 then flow into 
the circumference surrounding the preflowed solder layers 56 thereby 
improving the physical connection between the arms and the pads and 
contributing to the electrical connection between the arms and the pads. 
Solder terminals 24 form reliable soldered electrical connections with 
pads. These connections are more reliable than the connections formed 
using conventional solder terminals where discreet solder masses are 
physically secured remote from the contact site. During reflow soldering 
of these terminals the solder masses must melt and migrate to the contact 
site for forming a solder connection between the clip arms and the 
substrate pads. Difficulty is encountered in reliably flowing the molten 
solder into the interface between the clip arms and pads. 
While I have illustrated and described a preferred embodiment of my 
invention, it is understood that this is capable of modification, and I 
therefore do not wish to be limited to the precise details set forth, but 
desire to avail myself of such changes and alterations as fall within the 
purview of the following claims.