Note: Descriptions are shown in the official language in which they were submitted.
;Z57
EDGE TE~ ATlON FOR A~- ELECTRICAL CIRCUIT DEVICE
B k~round of the Inventio
~ he invention relates to electrical circuit de~-ices, and
particularly to a method and means for electrically connecting
S terminal leads, which extend outwardly from one surface of an
insulating substrate, to electrical circuitry deposited on an
adjoining surface of the substrate.
Over the past few years, there has been increased activity
in providing electrical circuit components as printed or
otherwise deposited configurations disposed on one or more
surfaces of an insulating substrate member. The material of
the substrate member is usually steatite, alumina or other ceramic
based composition. Although the deposition of the materials
required for supporting the elec'rical circuitry ls usually
quite sufficient with regard to the particular adjoining sur-
faces involved, very often it is difficult to insure that
there will be an adequate thickness of the deposition of con-
ducting edge termination material at the intersecting edse o
the two adjacent surfaces. The conductin~ edge termi~ation
material is arranged to complete the circuit between ~e-mination
leads extending outwardly from one edge and the adjacent intar-
secting surface which is intended to support the thick or thin
film circuitry deposited thereon. The edge termina~ion material
underlies the deposited circuit layer(s) and under a solder
layer on an adjoining surface in supporting contact with ter-
minal leads projecting outwardly from that surface. The cir-
cuitry may be relatively simple, as fo instance, a ~esistor
network, capaci_o. electrod~s or may inc'ude relatively cGmple~
semiconductor portions in ':he form of attached chip~ or othe_
devices which ccm~rise a h~brid assem~ly.
~'
Devices, such as those to be hereinafter described, are
made in relatively large quantities and are preferably arranged
for automated manufacture. That is, the leads are very often
attached by using conventional lead frame preforms, or other
support carriers for a multiplicity of leads, and are further
anchored to the substrate by means of solder applied with well-
known solder flow bath or similar facilities. Thus, the leads
may be initially held in place by wedging into a substrate
opening and transported through a solder flow bath, where the
solder will cling to the inner ends of the leads and to deposited
solder-accepting edge termination areas applied to a surface of
the substrate. The solder does not adhere to other portions of
the substrate or the circuit. Techniques of this nature are dis-
closed in the electrical circuit devices illustrated and claimed
15 in the Bartley et al U.S. Patent Nos. 4,127,934; 4,187,529 and
4,213,113, and the Beckman et al U.S. Patent No. 3,873,890, all
patents being assigned to the same assignee as the present inven-
tion. The first mentioned patent relates to a single in-line
packaging technique, (SIP), whereas the Beckman et al patent is
directed to a dual in-line package (DIP).
Inasmuch as the edge termination composition is con-
ventionally made from a material, such as silver, which tends
to go into solution with a later-deposited solder layer, there is
always present the possibility of leaching away of termination
; 25 material which has been deposited on the adjoining surfaces dur-
ing soldering operations. This deposition is usually applied
by a transfer roller and often is thinnest at the relatively
sharp edge defining the intersectiGn of the two angularly rela-
tive surfaces. The Applicants are aware of some manufacturers
who even go so far as to hand paint this sharp edge to insure
a greater thickness of termination material. Obviously, this
is a very expensive operation.
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The applicants in researching this problem conceived of the present
invention, which resides principally in provid;ng an indentation extending
between the adjoining surfaces and traversing the aforementioned relatively
sharp lines of intersection. This indentation may take the form of a simple
notch at the line of intersection, or is preferably provided by means of a
groove extending across the edge or surface which supports the terminal leads
of conventional parallelepiped-formed dual in-line or single in-line packaged
components, The groove finds its preference in the fact that molding dies
used to press the ceramic substrate to form are easier to machine with a
groove, as opposed to 6eing machined to provide a plurality of relatively
small protrusions arranged to form notched areas in the substrate. These
projections used for notching are also relatively small and subject to early
abrasive wear during use of the dies.
Summaryofthe Invent;on
This invention relates to an improvement in an electrical circuit
device including a substrate of electrically insulating material having a
first planar surface upon which is disposed an electrical circuit component;
an adjoining second generally planar surface angularly disposed relative to
said first planar surface; said planar surfaces conjointly defining a line
of intersection therebetween; an aperture extending inwardly from said second
planar surface and having its entrance opening solely confined to said second
planar surface; a terminal lead having a portion thereof seated within said
aperture and having its remaining portion extending outwardly from said
entrance opening; a conducting edge termination coating deposited transverse-
ly of said second planar surface and extending from said aperture over said
line of intersection and onto said first planar surface to pro~ide a
continuous path between said electrical circuit component and said terminal
lead; and a layer of conducting solder deposited on said edge termination
coating; the combination therewith of an indentation formed in said substrate,
said indentation traversing said line of intersection to communicate with
each of said planar surfaces and underlying said deposited edge termination
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i ~51257
coating; whereby an uninterrupted conducting path of solder and its under-
lying edge termination coating extends from said lead to connect with said
electrical circuit component.
The present invention contemplates a method and means for improving
and maintaining electrical conductivity in tfie edge termination layer
deposited in one surface of a substrate and extending over an intersecting
edge to an adjoining angularly disposed surface. The edge termination layer
is of a conductive material intended to continue the circuit between electri-
cal components supported by the substrate on the one surface and terminal
leads extending outwardly from the adjoining surface. The material is
compatible for electrical and mechanical connection with a solder layer
deposited for retaining and anchoring the respective leads of the device.
The substrate may be made of a ceramic material, such as alumina or steatite,
and is pressed or otherwise formed to include an indented area, which is the
subject of the present invention. The indented
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area may be in the form of a notch or an elongated groove inter-
secting both of the adjoining surfaces. The groove is preferably
formed in the substrate simultaneously with the pressing
operation. It will be apparent, that when necessary, and with-
S out departing from the invention, the groove or notch may be formedby abrasive,laser, or cutting operations after the substrate
has been formed. The indented area provides a channel for in-
suring adequate deposition of the edge termination material as
it traverses the adjoining surfaces. This is comparable to
providing a conducting "wire" running from a respective lead
attached to one surface, from the lead, across the edge ter-
mination surface supporting the lead, through the channel and
onto the first-mentioned surface for electrical connection with
circuitry supported by that surface.
Thus, any problems concerning leaching away of ter~.ination
material during the soldering operations will be minimized by
insuring adequate thickness of termination material as it
extends from one surface across the relatively sharp edge or
juncture between the adjoining surfaces.
Brief Description of the Drawings
Fig. 1 is a perspective view of a single in-line packaging
substrate suitable for use in the practice of the present
invention;
Fig. 2 is a perspective view of the substrate of Fig. 1,
illustrating the application of a layer of edge termination
material extending from the edge surface and over onto a top
surface relative to the view of Fig. 2;
Fig. 3 i5 a perspective view, including the edge ter-
mination material underlying a typical rasistive network cir-
cuit deposited on ~he upper surface of the substrate ofFigs. 1 and 2;
. llS1257
Fig. 4 is a perspectlve view of the finished product with
a conformal coating applied thereto and termination leads mounted
and soldered in place to provide a single in-line package;
Fig. 5 is a perspective view of a substrate provided for
aual in-line packa~ing, and further arranged to incorporate the
teachings of the present invention; and
Fig. 6 is a perspective view, partly in section, illustrating
a finished dual in-line package device in accordance with a
second embodiment of this invention.
Description of the Preferred Embodiments
An embodiment of the present invention is illustrated
in the views of Figs. 1-4, inclusive. With reference to Fig. 1,
it will be observed that a substrate 10 in the form of a
parallelepiped is supplied to support electrical circuit com-
ponents and terminal leads, as will hereinafter be described.The insulating substrate 10 is pressed, or otherwise formed,
from a ceramic material, such as alumina or steatite, to pro-
vide opposed upper and lower planar surfaces 11. Depending
from, and angularly relative to, the planar surface 11 is a
side or edge surface 12. This surface 12 is preferably planar
and disposed normal to the surfaces 11.
Either one or both of the surfaces 11 may contain the
electrical circuitry, which may be in the form of a network
of resistors, a combination of resistors and capacitors and
semiconductor chips, or chips of capacitors or the like. This
circuit configuration is made in accordance with known techniques,
and does not form a particular part of -the present invention.
The single in-line packaged (SIP) device presented ~y the views
of Figs. 1-4, inclusive, has ~een previously disclosed and
claimed in U.S. Patent No. 4,127,934, assigned to the same
assignee as the present invention.
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As was stated in that patent, the side or edge surface 12
includes a plurality of spaced apart openings 15 traversing the
substrate 10 from the edge surface 12 all the way through to
the opposite edge 13. These openings or apertures 15 are arranged
to receive terminal leads, as will hereinafter be described.
For the purpose of spacing the edge surface 12 from a circuit
board or other supporting means, the substrate 10 is provided
with a pair of forwardly projecting standoffs 16 and 17.
Particular attention is drawn to the indentations in the
form of grooves 18, which are formed in the edge wall 12, and
which also indent inwardly of the planar s-urface 11. These
indentations are an important part of the present invention,
and will hereinafter be described in detail. For the present,
it is important to note that the grooves may be "V" shaped as
shown, or may be rounded off ~not shown) in a general "U" shape, or
semicircular, where so desired. Although another embodiment will
be described, the present embodiment is preferred at this time,
since it is more facilely and inexpensively provided under
known molding and pressing techniques. Although not specifi-
cally shown, it will be apparent that the molding dies are moreeasily made to form the continuous groove 18 disposed for the
entire length of the edge surface 12. The second embodiment
illustrated in the views of Figs. 5 and 6 utilizes indentations
in the form of notches, but the notches are necessarily small
when compared to the elongated grooves 18. For instance, the
presently described substrate has approximate overall dimensions
of 0.78" x 0.30" x .08" with grooves 18 being only approxi-
mately 0.01" wide at the outermost dimension. Obviously,
notches are even smaller and the machining of pressing dies
for forming this configuration is very detailed and complex.
With reference to Fig. 2, the substrate 10 is provided
with edge termination areas 20. The areas 20 are transfer
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11512S7
printed by means of a transfer wheel tnot shown) laying down
a conducting material, such as silver paste, which extends across
the face of the surface 12, and preferably a bit inwardly of the
openings 15. The areas 20 also overlap the surface 11, as
shown at 21. This overlapping area 21 connects the electrical
circuitry to the edge of the substrate 10, as will later be
explained. The material of the termination areas 20 (in this
case silver paste) is well-known, and is compatible with solder
for connecting to terminal leads. After application, the silver
paste edge termination material 20 is fired on the substrate
in the usual fashion.
Particular attention is drawn to the fact that the ter-
mination material in the areas 20 nearly fills the grooves 18
to serve as a "wire-like" conductor passing from the holes or
apertures 15 over and onto the overlapped areas 21 of the sur-
face 11. This arrangementassures adequate thickness of the
edge termination material. It is well-known that, although
silver paste materials are ideal for serving as conductors and
for compatibility with known solders, they also have the dis-
advantage of tending to migrate into molten solder. The solder,as will later be explained, is deposited in automatic equipment,
as fully described in the aforementioned ~artley et al related
patents and represented by U.S. Patent No. 4,127,934, using
wave solder baths and other known automatic t~chniques As
much as the entire process of depositing the edge termination
areas 20 and later described soldering techniques is intended
to be fully automatic, slight variations in processing can lead
to the application of a relatively ~hin layer at the line of
intersection 25. This relatively .hin coat will ~end to leach
away from the substrate and migrate in'o the later applied
solder. The present invention therefore contemplate~ providing
the "wire-like" conductive path to insure proper conductivity
between the areas 20 and 21.
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3 ~S~7
With reference to Fig. 3, it will be observed that a -~fpical
resistive network may be laid down on the sur~ace 11 with known
techniques utilizing thick or thin film material, such as the
well-known cermet resistor materials, one of which is described
in the Brandt et al U.S. Patent No. 3,639,274, assigned to the
same assignee as the present invention. The particular com-
position does not form a par~ of the present invention.
The resistive areas are denoted by the reference char
acter 26, and in the case of cermet material, are screen printed
or otherwise deposited to extend over the previously laid down
conductive paths 27 which extend into and overlap the edge
termination areas 21. Without going into the details of the
circuitry, the conductive strips 27 are also of a glassy
matrix, including highly conductive metallic materials inter-
mixed therewith. The layers may be fired indiv.dually cr co-
fired as desired. It is generally preferred to provide the
conductive paths or layers 27 of material that resist adhesion
to solder, to assist in preventing solder from adhering to
portions of the substrate where it is unwanted. For this
reason, it is also preferable to permit a small portion to
slightly overlap the termination material 20 at the upper edge
of the planar surface 12.
As illustrated in Fig. 4, leads 30 are inserted in each
of the respective openings 15 in the manner disclosed and claimed
in U.S. Patents No. 4,127,934, 4,187,529 and 4,213,113. As
aforementioned, solder pads 31 are automatically applied by
transporting the substrate 11, with theleads 30 attached thereto
through a waveform solder bath (not shown). During this assembly
process, the leads are preferably attachPd to a carrier strip
o~ a lead frame (not sho~n) as disclosed in .he aforementioned
patents.
It is preferred to provide a conformal coating 32 as a
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l~S~2S7
means of protecting the resistive and conductive layers 26
and 27, respectively, from the elements. Identification (not
shown) may be printed directly to the conformally coated sur-
face. The solder pads 31 serve to provide additional con-
ductivity from the edge termination material at the areas 20and overlapping into the areas 21 to connect with the network.
The solder pads 31 act to also provide an additional anchoring
means for the leads 30.
The embodiment of Figs. 5 and 6 illustrate another
technique of providing the indented areas, which are the sub-
~ect of the present invention. It will be apparent that
either the grooved indentations illustrated in the views of
Figs. 1-4, or the notches 35 may be utilized in either the
SIP or the DIP devices with even facility. The two different
devices, i.e. SIP and DIP, are merely shown as examples to
indicate broad application of the present invention, which also
may reside in various configurations of indented areas tra-
versing between two adjoining planar surfaces, i.e. surfaces
at 11 and 12 of the SIP construction of Figs. 1-4 and planar
surfaces 36 and 37 defined by the line of intersection 38
of the substrate 40 of Figs. 5 and 6. The embodiment of
Figs. 5 and 6 is explained in detail in the Beckman et al
U.S. Patent No. 3,873,890, assigned to the same assignee as
the present invention.
Suffice it to state that the dual in-line package con-
struction of the device of Figs. 5 and 6 comprises a substrate
40 having a surface 36 arranged to receive a thick or thin
film network 42 comprising a resistive layer 43 connected to
leads 44 by means Gf conducting paths 45 overlyillg termination
pads 46 which extend from the surface 35 over the line of
intersection ~8 and onto the edge termination portion 47 of
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the edge 37. Solder pads 48 are applied as described in con-
nection with the discussion of the first embodiment. A con-
formal coating 50 is later applied after the leads 44 have
been anchored in place.
It will be observed that the notched areas extend between
the planar surfaces 37 and 38 to provide a means of increasing
the thickness of the edge termination coating overlapping both
surfaces 36 and 37 and intersecting the line of intersection 38.
This wire-like conductive path assures adequate thickness of
termination material to minimize the deleterious effects of
"leaching" or migrating of silver into the solder as the solder
is applied to retain the leads in place.
Although the invention herein has been specifically de-
scribed in connection with devices having leads projecting from
one or more sides of a substrate, it will also be understood
that, such as in the case of certain hybrid circuits (not shown),
the provision of the notches 35 or grooves 18 is equally appli-
cable to devices which have no leads. In fact, the invention
finds application in instances where solder is not applied.
The channels defined by the notches 35 or grooves 18 provide
a ready means of assuring adequate "flow" during printing or
other deposition of a layer, such as the edge termination areas
or portions 21 and 46.
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