Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-02-08
2001-10-02
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S874000, C439S083000, C439S876000
Reexamination Certificate
active
06295726
ABSTRACT:
The invention is related to a method of manufacturing surface-mountable SIL hybrid circuits, and, especially, to the manufacturing phase in which the SIL hybrid circuits are provided with external contacting leads by means of a lead frame. The invention relates also to mounting of SIL hybrid circuits on a base substrate, e. g. a printed circuit board, by means of surface mounting techniques.
Even in the past decade hybrid circuits were used widely in the electronic equipment because by using hybrid circuits the packaging density was increased in relation to a technique in which mainly separate components provided with contact terminals were mounted directly on a printed circuit board. It is obvious that packaging density is most easily increased by using SIL hybrid circuits (SIL, single in-line), i. e. edge-mountable hybrid circuits, the conventional packaging technology of which is illustrated in FIG.
1
. One edge of a SIL hybrid circuit
1
is provided with contact areas
7
,
7
′. The leads
3
,
4
, which are to be connected to the contact areas, are arranged to form a continuing lead frame
2
, and they are connected, usually by soldering, without separating them from the frame. In
FIG. 1
, this is shown as a front view (above left) and as a side view (above right). After connection of the leads, the side bands
5
,
6
holding the frame together are removed, and the leads
3
connected to the contact areas
7
,
7
′ by means of the clip parts
4
a,
4
b
remain at the edge of the hybrid circuit
1
. Below left in
FIG. 1
, mounting of the hybrid circuit separated from the frame
2
on a circuit board
11
is shown schematically. The holes
12
which receive the leads
3
of the hybrid circuit are plated through holes for making the solder joints reliable.
Today the packaging technology of electronic equipment often includes multilayer circuit boards and surface mounted components on both sides of the circuit board. There are several reasons which make the SIL hybrid technology described above not very suitable for present packaging technology. Firstly, the borings necessary in the circuit board reduce the area available for inner circuit layers. Secondly, instead of wave soldering normally used when mounting components to plated through holes, reflow soldering methods, which are more suitable for surface mounting, are used in the present packaging technology. In the wave soldering process the components on the lower side of the circuit board are immersed in the liquid solder, whereby the thermal shock may damage them. If hybrid circuits are used, they are often mounted separately and soldered manually to avoid reliability risks.
The use of hybrid circuits in electronic equipment is remarkably reduced also because a high enough packaging density is achieved by mounting small size surface-mount components directly on a multilayer circuit board. In the design of many electronic devices it is, however, still desirable to improve packaging density, and by means of SIL hybrid circuits it would be possible. Only a new advantageous solution, suitable for the present packaging technology, for mounting SIL hybrid circuits on printed circuit boards is needed. An object of the invention is to provide such a solution.
According to the invention, a method of manufacturing SIL hybrid circuits with terminal leads (legs):
a lead frame is manufactured including side bands and between the side bands several members including a clip member for making a joint to a hybrid circuit and a foot member for surface-mount to a base substrate, e. g. a printed circuit board;
a hybrid circuit is attached to the clip members of the lead frame by means of the corresponding contact areas; and
excessive parts are removed from the lead frame so that the clip members attached to said contact areas and the corresponding foot members are left,
wherein the lead frame is manufactured and/or the excessive parts are removed therefrom so that one or more support members are left with respect to one SIL hybrid circuit for supporting the same during positioning and surface mounting to a base substrate.
In accordance with a preferred embodiment of the invention the lead frame is manufactured to include strip-like members connecting the foot members to the side band so that at least one strip-like member may be left as a support member with respect to one hybrid circuit during the removing of the excessive parts.
In accordance with another preferred embodiment of the invention strip-like members are left which extend from a foot member to both sides of the SIL hybrid circuit. The strip-like member left as the support member may be bent towards the base substrate for the purpose that, during mounting the SIL hybrid circuit, it is positioned into a corresponding hole formed in the base substrate. The bent part of the strip-like member may also be twisted around the longitudinal axle thereof, whereby the bent parts twisted to different directions improve the alignment of the hybrid circuit.
In accordance with a further embodiment of the invention the location of the support member to be left is selected with respect to any SIL hybrid circuit to be advantageous with respect to the mounting, so that, for example, in the mounting of the SIL hybrid circuit on the base substrate the position of the support member is different from the positions of the support members of the adjacent hybrid circuits.
The method according to the invention makes possible to utilize SIL hybrid circuits efficiently in surface-mount based assembly of electronic equipment. The circuits may be mounted by automatic mounting machines, and they are well enough supported so as to remain stationary during reflow soldering.
REFERENCES:
patent: 3873890 (1975-03-01), Beckman et al.
patent: 4127934 (1978-12-01), Bartley et al.
patent: 4978307 (1990-12-01), Billman et al.
patent: 5352851 (1994-10-01), Wallace et al.
patent: 5441430 (1995-08-01), Seidler
patent: 5490788 (1996-02-01), Mazzochette
patent: 5635760 (1997-06-01), Ishikawa
patent: 682 366 (1995-11-01), None
patent: 42 43 155 (1992-08-01), None
Arbes Carl J.
Nokia Networks Oy
Pillsbury & Winthrop LLP
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