System for detection of unsoldered components

A system for detecting certain improperly soldered electrical component connections to a printed circuit board includes methods and apparatus providing an automated means for detecting unsoldered component leads is disclosed. A connection pad divided into two portions, or land areas is bridged by the component lead when soldered. A test pad connected to one of the land areas provides a test point for detecting the presence or absence of an open circuit condition through the lead of an electrical component to a point in the circuit to which it is to be electrically connected.

FIELD OF THE INVENTION 
This invention relates to the manufacture of circuit boards, and more 
particularly to a system including methods and apparatus for automatic 
testing of solder joints of surface mounted and other electronic component 
lead connections. Further, solder connections of components and devices 
that are otherwise untestable by conventional electrical methods of 
circuit board testing are susceptible of testing according to the methods 
and apparatus forming the present system. 
BACKGROUND OF THE INVENTION 
The technological advances made in semiconductor processing have enhanced 
soldering of surface mounted electronic components to conductor pads on 
etched circuit boards. These circuit boards are generally known as printed 
circuit boards without regard to the method of forming the circuit traces 
on the insulating substrate. The economies of scale resulting from this 
advance have led to the predominance of printed circuit boards for surface 
mounted devices. Numerous different components and devices (collectively 
"components") can be surface mounted. 
By placing test pads and contacts at specific electrical and/or physical 
board locations, most circuits and components may be tested for quality 
control by automated test equipment. For various reasons, certain 
components (including certain surface mounted components) do not lend 
themselves to direct electrical testing. Thus, the technology presently 
known is unable to provide for the electrical testing of either the 
component or the reliability of the solder connection(s) to it, once the 
soldering assembly is completed. Examples of such components include 
intrinsic safety components, surge suppressors, gas discharge tubes, 
certain semiconductors, and myriad other components. Only costly visual 
inspection of the connections to these components can be performed to 
ensure that they are properly soldered. 
Occasionally, component to solder pad connections that remain unsoldered 
may be difficult or impossible to detect. This is especially true of the 
untestable components previously discussed. Often, through partial 
physical contact of a component lead and its respective solder pad, the 
component may still function sufficiently well to pass an initial 
electrical inspection, at least until shock, vibration, oxidation, and/or 
corrosion degrades the electrical contact. This defect may be difficult to 
detect since an intermittent electrical connection may be present when the 
component or circuit functionality is tested. Often, these improper 
contacts are very difficult to locate and identify, even under repeated 
visual inspection. 
Automatic testing techniques typically test the electrical or electronic 
functionality of the components. The equipment and methods for practicing 
automatic testing are well known to the person having ordinary skill in 
the art. Automatic testing techniques are desirable since they are faster 
than manual testing techniques, more efficient, generally more reliable, 
and more cost effective. Automatic continuity/value testing cannot, 
however, be used with many of the foregoing special components. Often, 
these components cannot be electrically tested because testing would 
destroy the component for its intended function. However, it may still be 
necessary to verify the solder connection of each component lead to ensure 
that electrical connection is made. Presently, this inspection must be 
performed visually. A reliable electrical test of the connection would be 
preferable, especially if performed with conventional automatic test 
equipment and testing processes. Automated test of these special 
components cannot be performed at present since there is no mechanism that 
can test the solder connection of each lead of these components in an 
automated manner. 
The use of test pads connected to component leads is well known. Such test 
pad connections provide an electrical connection point for the known 
automated means for testing electrical connections between various devices 
and for testing the component functionality. However, there is no 
automated mechanism directed to testing for the presence or the mechanical 
stability of the solder joints of individual component leads to the 
circuit board. When the component can be automatically tested, an 
unsoldered lead may go undetected if it does not affect the electrical 
functionality of the tested component(s) at the time of the test. 
U.S. patent application Ser. No. 08/451,954, filed May 26, 1995, assigned 
to the assignee of the present invention, discloses a system and method 
for detecting unsoldered thru-hole component connections. The teaching of 
U.S. patent application Ser. No. 08/451,954 is hereby incorporated herein 
in its entirety. 
In Ser. No. 08/451,954, a peripheral land area is positioned very closely 
circumjacent the land area of a thru-hole on one or both sides of a PC 
board, through which thru-hole a component lead is inserted. The 
circumjacent land area(s) may be connected to one or more test pads. The 
separation between the thru-hole land area and the circumjacent land area 
forms an isolation gap which is very narrow; it is easily bridged by 
flowing solder over the separation. Thus, application of solder to secure 
the components to the thru-hole land area of the PC board effectively 
bridges, by surface tension of the molten solder, the narrow space between 
the thru-hole land area and the circumjacent land area connected to the 
test pad. When the soldering process is completed, measurement of 
electrical conductivity between the test pad(s) indicates that the 
component lead is properly soldered on both sides of the board. No portion 
of the component lead is ordinarily used in bridging the gap. 
U.S. Pat. No. 4,091,529 to Zaleckas illustrates a bifurcated component 
connect lead area on a printed circuit board, joined by the circuit board 
trace at a location spaced apart from the connect land area. The document 
does not address automated testing of unsoldered component leads. 
U.S. Pat. No. 5,308,928 to Parla et al discloses a method and structure for 
manufacturing printed circuit board traces in which multiple land areas 
are formed at open areas of the board and in such close proximity to one 
another that an intentional interconnect can be formed between many of 
them by solder bridging. A multiplicity of such interconnect areas enables 
manufacture of a minimal number of printed circuit boards to each meet the 
multiple connection possibilities of multiply functional printed circuit 
boards. The document does not address the problem of defectively soldered 
component leads or automated testing of unsoldered component leads. 
Accordingly, where the component is not susceptible of direct electrical 
testing there exists no technique for automatically detecting unsoldered 
component leads. Only a manually performed visual check of each such 
solder connection can detect such defective solder joints. 
SUMMARY OF THE INVENTION 
A system for detecting unsoldered component leads is disclosed. The system 
includes related methods for making printed circuit boards and for 
testing, especially automated testing, for failed solder connections. At 
the circuit board level, the invention consists of a specially configured 
component solder connection pad. A unitary connection pad is ordinarily 
formed at the point of board contact for each of the component leads. This 
pad serves to form a solderable surface for securing the component lead to 
the printed circuit board and for establishing an electrical connection 
between the component and the remaining board circuitry. 
It is an object of this invention to provide a system for detecting 
unsoldered component leads that increases the quality assurance of the 
finished assembly, yet does not significantly increase the cost of the 
printed circuit board. 
It is an object of this invention to provide a method of making printed 
circuit boards that enables testing of component lead soldering. It is a 
feature of this invention that the solder connection of component leads 
can be tested without subjecting the component, per se, to an electrical 
current. 
It is an object of this invention to provide an automatic testing technique 
for detecting unsoldered component leads. It is a feature of this 
invention that the solder connections of component leads can be tested by 
conventional automatic testing equipment and methods, even where the 
components per se cannot be tested by electrical methods. 
It is a further object of this invention to provide a system as described 
above that does not affect the existing circuit or component integrity. 
A system for accomplishing the objectives of detecting unsoldered circuit 
board component leads according to this invention includes a circuit card 
having at least one surface and at least one solderable connection pad on 
the surface positioned to underlie a specific component lead and connected 
to a circuit path on the circuit card. The connection pad is separated 
into first and second unconnected land areas and at least one component 
having at least one electrical connection lead is located for solder 
connection to the connection pad. The land areas of the connection pad are 
disposed such that electrical connection between the first and second land 
areas is completed upon solder connection of the component lead to the 
respective connection pad. 
One method of the present invention is directed to producing circuit cards 
for meeting the foregoing objectives comprises the steps of providing a 
circuit card substrate having at least one surface and forming at least 
one solderable connection pad on the surface positioned to underlie a 
specific component lead. The pad is divided into first and second land 
areas electrically isolated by a separation of the first and second land 
areas from one another. The separation of the first and second land areas 
is to be sufficient to prevent joining them by surface tension of liquid 
solder alone. The first land area is connected to a circuit path on the 
circuit card. It may also be connected to a test pad or test point. 
A conventional solder paste layer, preferably having adhesive properties, 
is applied to portions of the surface through a mask, including the first 
and second land areas. A separate mask may be used to apply a plating 
resist in order to prevent plating thereof by a plating solution. The 
solder paste mask may be configured to prevent application of solder paste 
to the area separating the connection pad land areas. The component lead 
is then applied to the paste for soldering. It is held in place by the 
adhesive qualities of the solder paste. 
Another method of the present invention relates to detecting unsoldered 
circuit board component leads according to these objectives includes the 
steps of providing at least one solderable connection pad on a surface of 
the circuit board including first and second land areas electrically 
isolated by a separation of the first and second land areas from one 
another. The separation of the first and second land areas is to be 
sufficient to prevent joining them by surface tension of liquid solder 
alone. The first land area is conventionally connected to a circuit path 
on the circuit card. It may also be connected to a test pad or other test 
connection point. A solder paste is applied to the connection pad, and the 
component lead is positioned onto and pressed into the paste, which 
temporarily holds the component lead in place for soldering. Again, the 
solder paste mask may be configured to prevent application of solder paste 
to the area separating the connection pad land areas. The first and second 
land areas are then electrically connected by soldering the component lead 
onto and joining the first and second land areas to form a single 
connection pad area. Electrically testing the continuity of the connection 
pad between the first and second areas then ensures detection of most 
defective solder faults of these split pad connections. 
A method for producing circuit cards that facilitates detection of 
unsoldered component leads, includes the steps of providing a circuit card 
substrate having at least one surface, then forming at least one 
solderable connection pad on the surface positioned to underlie a specific 
component lead. The connection pad is to include first and second land 
areas electrically isolated by a separation of the first and second land 
areas from one another. The separation of the first and second land areas 
is to be sufficient to prevent joining thereof by surface tension of 
liquid solder alone. The first land area is connected to a circuit path on 
the circuit card. It may also be connected to a test pad or other test 
point. 
A coating is then applied to portions of the surface to prevent plating 
thereof by a plating solution, including the separation between the first 
and second land areas. Then a plating solution is applied to areas of the 
surface in the absence of the solder mask, wherein the coating applied to 
the separation of the first and second land areas is insufficient to join 
them by surface tension of the plating solution. Thereafter, a solder 
paste layer is applied in a coating of predetermined thickness to selected 
areas through a mask. As before, the solder paste mask may be configured 
to prevent application of solder paste to the area separating the 
connection pad land areas. Component leads are applied to, and pressed 
into, the solder paste. The component leads are thereafter soldered to the 
board by heating the solder paste in the known manner. 
In the present invention, the connection pad is formed on the circuit board 
in a divided state, separated into two (or more) unconnected portions, or 
separate land areas, by an insulating gap. The component lead electrically 
bridges and mechanically joins the lead to the two connection pad land 
areas when it is sufficiently soldered to form an acceptable joint. It is 
a feature of the present invention that the connection pad associated with 
a given component lead thus becomes a single electrical entity when the 
two lands are joined by the component lead soldered to the board. 
This electrical connection between the land areas is used to test the 
continuity across the land areas of the connection pad to detect any 
unsoldered component leads. 
It is an advantage of the present invention that testing the electrical 
continuity through the (at least) two land areas provides an improved test 
of whether the connection is properly soldered. This test may be readily 
adapted to conventional automated test procedures. Continuity testing may 
be performed directly through the bridged connection pad land areas if 
they are of adequate size and access is available, or through one or more 
test pads connected to the respective land areas by circuit paths. 
Test pads may be formed on the circuit board, each pad usually being 
located in close proximity to one or more leads of an electrical component 
if it is desired to provide a conventional test pad surface to facilitate 
automated testing. Such test pads should be easily accessible by an 
automated testing apparatus. A respective test pad may be connected to 
only one, or to both land areas of the connection pad. Other test points 
may also be used. 
The configuration of the separating division or gap between the first and 
second land areas can be embodied in various geometric shapes and sizes. 
However, it is preferred that emphasis be placed on a design that 
preserves and maintains the integrity of the main circuitry. The 
connection pad may also be divided into more than two land areas. 
Conductivity may then be checked across the entire connection pad, 
including through two or more land areas. 
In a first configuration, the separation path of the connection pad 
division is to be rectilinear. That is, a straight linear separation path 
may be used. A series of straight paths displaced at angles to one another 
may also be used. In one variation, the separation path may be angled to 
improve the reliability of the solder bridging due to solder flow dynamics 
of the soldering process. This may be especially effective with certain 
component placement and soldering processes. The separation path of the 
connection pad division may also be curvilinear in additional 
configurations. 
Additional consideration may be given to the shape, size, and disposition 
of the component lead to be soldered. A separation across the width of an 
elongated connection pad may be preferred for a lead having an elongated 
axial dimension, such that the long component lead ensures effective 
bridging of the separation gap. For certain discrete components designed 
especially for surface mounting to printed circuit boards and having a 
multiplicity of closely parallel contact leads, the connection pad land 
area may be lengthened along the axis of the component lead and a dividing 
separation gap formed normal with respect to the length of the component 
lead. Similarly, a wider component lead may suggest a separation normal to 
the width of the connection pad for a lead having a wider contact surface 
provided by the wider component lead. Such a configuration may also 
facilitate desirable positioning of a test pad. 
It is generally preferred that a substantially uniform distance be 
maintained across the separation gap width. Due consideration should be 
given for etching limitations according to the pattern of the separation 
gap. 
In any configuration, the test pad(s) may be so disposed as to provide 
convenient access by automated testing equipment. Thus, the present 
invention may be used with known automated test equipment to detect the 
absence or failure of a component connection to a connection pad through a 
failure to form a solder bridge that includes both the first and second 
land areas and the component lead. 
Other general and specific objects, features, and advantages of this 
invention will be apparent and evident from the accompanying drawings and 
the following detailed description of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Apparatus and methods for providing automated detection of unsoldered 
component leads is disclosed in FIGS. 1 through 6. The first side of a 
printed circuit board 20 corresponding to the component side is shown in 
all figures. 
Referring now to FIGS. 1 through 4, printed circuit board 20 contains a 
component soldered to one or more solder pads on the surface of the 
printed circuit board in accordance with the present invention 10. 
FIG. 1 shows a test pad land area or etch 36 is positioned within close 
proximity to a component pad 24 composed of electrically separated land 
areas 26 and 30. The test pad 36 can be used by an automatic testing 
device to test the electrical connection between a lead 18 extending from 
component 22 and the test pad 36 once the lead 18 is soldered to both of 
the land areas 26, 30 that form the component connection pad 24 on the 
printed circuit board 20. The presence of an electrical bridging 
connection 32 between the first and second land areas of the connection 
pad 24 is used to indicate that the lead 18, and thus component 22, is 
successfully soldered to the printed circuit board 20. 
In the first embodiment shown in FIG. 1, connection pad 24 is composed of 
first and second land areas 26, 30 joined by the bridging component lead 
portion 32 and then via conductive trace 34 to the test pad 36. The 
portion 32 of the lead 18 serves to form an electrical connection bridge 
between the first and second land areas to test pad 36 in order to enable 
tests of the connection pad 24 connection at 32 with conventional 
automated test equipment. The respective land areas 26, 30 and the test 
pad 36 can be formed of any conventional conductive material such as 
copper, that is preferably covered with a layer of solder or solderable 
plating or the like before mounting the components. Another test pad 38, 
such as is ordinarily used for testing at the component lead end, may be 
connected via path 28 to the connection pad 24 first land area 26. 
Solder in the form of a paste 40 may be used to join the component leads to 
the land area portions. This is especially so for chip type and other 
surface mount components such as shown in FIGS. 2-4 (solder paste 40 not 
shown in FIGS. 1-3). The solder paste typically includes entrained 
microcapsules of solder distributed throughout a sticky flux. Kester Corp. 
type R244 solder paste, catalog number 58-3301-1601-NS is believed 
suitable. AIM type SN 63.sub.-- NC291AX.sub.-- 90-75-70 may also be used. 
Heating the solder paste melts the solder 40 therein and causes it to 
flow, joining the component leads (e.g., 18, etc.)to the land areas 26, 
30, etc.) Alternately, solder may be applied by other methods known to 
those persons having ordinary skill in the art. 
The separation distance between land areas 26 and 30 should be selected to 
provide for at least a minimal spacing value over a non-conductive 
material to avoid unintentional solder bridging. A mask of insulating 
material that resists solder bridging may be used to enhance the spacing. 
The spacing and mask material are selected with due consideration given to 
standard circuit board preparation and processing techniques. This spacing 
can be accomplished over any insulating substrate material such as 
conventional circuit board material 20. The narrower is the spacing, the 
easier it is to form the conductive solder bridge with lead 18 during 
component 22 installation. However, the spacing must also be wide enough 
to reliably electrically isolate the two land areas 26, 30 before 
soldering the component 22 lead 18 to those land areas. That is, the 
spacing must be great enough to eliminate liquid solder bridging due to 
surface tension, capillary action, or the like without the presence of 
lead 18. 
A preferred spacing for most surface mount components ranges to no more 
than about 0.030 inches, and preferably from about 0.005 to about 0.006 
inches. It is believed that selection from among the many solder paste 
products available, and especially that both the area and layer thickness 
of the solder paste, will affect the soldering process due to surface 
tension of the molten solder and/or capillary action. These factors must 
also be considered in determining an appropriate spacing. However, the 
invention as broadly claimed is not to be interpreted as being limited to 
any particular land area spacing dimension. The choice of spacing 
dimensions, paste area, and paste thickness are preferably based on the 
paste material used, manufacturing considerations such as cost of 
manufacture, and the ease in forming a solder bridge with component lead 
18 with the selected solder process. 
It is believed that a solder paste area which is great enough to 
substantially cover each land area is sufficient in combination with a 
layer thickness ranging from about 0.002 to about 0.012 inches, and 
preferably ranging from about 0.006 to about 0.008 inches. As layer 
thickness and/or volume of paste applied to each pad increases, it may 
become increasingly necessary to provide a separation of masked solder 
paste areas generally conforming to the separation between land ares. 
The exposed surface area of each of the land areas 26, 30 should be large 
enough to form a solder bridge while not requiring a large amount of 
circuit board space or a particularly large cross section of component 
device lead 18. A width between about 0.0125 to about 0.015 inches may be 
preferred for most discrete component leads. However, the invention as 
broadly claimed is not to be interpreted as being limited to any 
particular connect pad or component lead size. Rather, the emphasis is 
normally placed on conserving circuit board space, on ensuring adhesion of 
the component lead in the solder paste, the ease and reliably in formation 
of the solder bridge 32, and the ease with which automated testing can 
thereafter be carried out. Of course, with wide component leads (see FIG. 
2), wide connection pad land areas may be desired. 
Test pad 36 and circuit path 34 are used in connection with circuit path 28 
by a conventional automatic testing device to detect electrical 
connections through land areas 26, 30 forming connection pad 24, through 
the portion 32 of the component lead 18 that bridges the land areas. 
Typically, conventional automatic testing equipment can test the 
electrical conductivity of connections relative to two land areas of 
predetermined positions, that are usually conventional test pads. Test pad 
38 is connected via path 28 to the connection pad 24 first land area 26; 
it provides a test pad to test pad circuit path for testing the solder 
bridge 32. 
Test pads 36, 38 can be of a square, rectangular, circular, or other shape 
and are normally formed of a conductive material such as copper. The pads 
are preferably covered with a layer of solder or plating. They should be 
sized large enough to enable reliable contact by the automatic test 
equipment test probes. However, they need not be limited to a particular 
size, geometric shape, or plating layer. Other shapes and plating 
materials may be used so long the resulting test pads 36, 38 are suitable 
for the automatic testing device employed. Other electrically conductive 
configurations may also be used in place of the printed circuit board test 
pads, such as (but not limited to) test point pins and terminals, 
connectors, and the like. The geometric shape or size of conductive traces 
28, 34 should be selected to provide at least the minimum electrical 
conduction path needed to form the electrical connection between test pad 
38, land areas 26, 30, and test pad 36. 
Using current printed circuit board technology, conductive trace 34 can be 
formed of a conductive material such as copper and may be covered with a 
protective layer of non-conductive mask material if desired. Any solder 
mask material may be used. This mask is used primarily to ensure that 
solder does not form about the conductive trace during the soldering 
process. As discussed above, care should be exercised in the selection of 
the solder paste used, and more particularly, in the thickness of the 
solder paste layer and the area(s) covered. 
The system is advantageously applied to wide connection pads 12 as well, as 
is illustrated in FIG. 2. A component 52 is mounted to circuit board 20 
via a wide component lead 54 and soldered to a divided wide connection pad 
56. The solder paste 40 (not shown) stickiness may be reliably used to 
hold the component lead 54 to the connection pad 56 until soldering is 
completed. 
Pad 56 is formed of separate land areas 58 and 60. When properly soldered, 
lead 54 electrically connects land areas 58 and 60. A normal circuit path 
62 is completed between first land area 58 and another circuit portion. A 
test pad 42 may be connected to land area 58 through a circuit path 44 
when the land area 58 is not otherwise easily accessible by the automatic 
electrical testing equipment. Second land area 60 is electrically 
connected to test pad 64 through circuit path 66. Wide connection pad land 
areas may be essential in some applications, e.g., where they are used for 
ground planes, thermal dissipation, or greater current carrying 
capability. 
In FIG. 3, selected portions of a multiple lead component device such as an 
IC chip are shown soldered to a printed circuit board 20. An electrical 
component 68 having one or more leads 70, 72, . . . , .sup.n is placed 
onto the printed circuit board 20 from the component side with the leads 
70, 72 stuck to the respective connection pads by solder paste 40 (not 
shown). The leads are positioned to join the respective pairs of land 
areas 74, 76 and 78, 80. Each lead is then soldered (by heating the solder 
paste) to the board 20 to thereby secure the lead to the printed circuit 
board. Typically, a good solder connection will result in solder flowing 
so that a respective solder bridge 82 is formed together with each lead 
70, 72 across the respective gap between the two land areas 74, 76 and 78, 
80 that form each completed connection pad to bridge the spacing. The 
bridge electrically connects the first and second land area portions of 
the connection pad. Circuit paths 90, 92 lead to the respective test pads 
86, 88. The additional soldering should not ordinarily require any 
increase in the manufacturing time of the printed circuit board. It 
provides a system for testing the connection between the respective test 
pads 86, 88 and the respective land area pairs 74, 76 and 78, 80 that are 
joined electrically by the leads 70, 72. The bridging of the separated 
land areas enables the connection of the individual lead 70, 72 to the 
printed circuit board 20 to be tested, and especially by known automatic 
testing equipment using test pads 86, 88 and circuit paths 96, 98. This 
conductivity test will detect the presence of any unsoldered leads. 
It should be noted that the invention disclosed herein greatly enhances the 
reliability of the printed circuit boards at reduced cost by testing for 
electrical continuity between the land areas of selected component 
connection pads. However, the reliability of the continuity tests may be 
defeated by component leads that are not, in fact, properly soldered to 
their respective connect pads. Additional certainty can be obtained by 
dividing the connect pad into a greater number of land areas and testing 
continuity among all of them. For example, the connect pad can be divided 
into first, second, and third land areas (not shown) in which the 
component lead is soldered to all three land areas. Continuity can be 
tested from a center, or second land area that is positioned between outer 
first and third land areas. Testing the continuity to land area two 
through land areas one and three, all connected by a soldered component 
lead bridge, will enhance reliability where a greater level of connection 
certainty is required. 
A discrete component 41 adapted for surface mounting by a solder paste to 
the printed circuit board 20 is illustrated in FIGS. 4A and 4B, another 
embodiment 16 for testing discrete component solder connections to printed 
circuit board pads 50, 94 via conventional test pads 46, 48. Solder pads 
50, 94 represent land areas, separated by a narrow isolation region. Bands 
of conductive solderable material 40A as known in the art are formed on 
the ends of component 41 for soldering to the printed circuit board 16 
through the medium of the masked solder paste 50A, 94A areas on the 
connection pads 50, 94. The pads 50, 94 are of smaller area than a 
conventional surface mount component 41 pad area in order to provide for 
the separation therebetween. Each side of a given end of the band 40A is 
disposed over one of the respective pads 50, 94. Together, they form a 
conventional pad when bridged by both sides of the one end of the 
component 41 solderable material 40A band. 
The "popcorn" effect arises when a surface mount component 41 is not 
soldered substantially flush and square with the printed circuit board 20. 
Component 41 is correctly soldered as shown in FIG. 4A. In FIG. 4B, 
component 41 is shown improperly soldered to the board, with one end 
unconnected. This is characteristic of the "popcorn" effect. In FIG. 4B, 
the band 40A typically does not connect pads 50, 94; that is, the 
conductive bridge between pads 50, 94 is missing in this position. 
The presence or absence of the component 41 soldered to both the pads 50, 
94 is detected conventionally by the presence or absence of a low 
resistance path from a test pad 46, solder pad 50, solder 50A, through the 
component 41 end band 40A, solder 94A, and solder pad 94 to test pad 48. 
When the path is incomplete, the connection of component 41 to pads 50, 94 
cannot be assumed. 
Turning now to FIGS. 5 and 6, a number of examples are shown of useful 
patterns for the connect pad land areas on the printed circuit board 20. 
In FIG. 5, for example but not limitation, several linear gap geometric 
patterns 100, 110, and 120 are shown. Curvilinear separation gap patterns 
are shown in FIG. 6. The solder paste (not shown in FIGS. 5 and 6) is 
applied over these connect pad land areas to secure the component leads 
until soldering is completed. 
Connect pad 100 includes first and second land areas 102, 106 diagonally 
separated by a narrow gap 106 that also cannot be bridged by surface 
tension of molten solder. Connect pad 110 includes first and second land 
areas 112, 114 rectilinearly separated by gap 116, that also cannot be 
bridged by surface tension of molten solder. The component lead (not 
shown) normally extends along the central portion, or spine, of the pad 
110. However, when the component lead does not fall along the spine, a 
bridge may be formed anywhere along the gap 116 between the two land areas 
112, 114. Similarly, connect pad 122 includes first and second land areas 
122, 124 rectilinearly separated by a partially diagonal gap 126, that 
again cannot be bridged by surface tension of molten solder. While the 
component lead (not shown) normally extends along the central portion, or 
spine, of the pad 120, when the component lead does not fall along the 
spine, a bridge may be formed anywhere along the gap 126 between the two 
land areas 122, 124; it is highly likely that the diagonal portion of gap 
126 will be bridged. 
The curvilinear gaps 136, 146, and 148 are selected to ensure that the 
component lead (not shown) to be soldered to the printed circuit board 20 
bridges the gap 136, 146, or 148, between the respective land area pairs 
132, 134; 142, 144; and 152, 154, thus allowing for great variance in lead 
placement which will reliably connect to connect pads 130, 140, or 150, 
respectively. 
The aforementioned disclosure presents a method and apparatus providing an 
automated system for detecting the presence of unsoldered component device 
leads. 
Although the preferred embodiments of the invention have been described 
hereinabove in detail, it is desired to emphasize that this description is 
provided for the purpose of illustrating particular embodiments of the 
invention and thereby to enable those skilled in the art to adapt the 
invention to various different applications that may require modifications 
to the apparatus described hereinabove. Thus, the specific details of the 
disclosed embodiments illustrated herein are not intended as limitations 
on the scope of the present invention other than as required by such prior 
art teachings as may be found pertinent to this invention.