Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-06-20
2003-02-18
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S266000, C361S792000, C361S795000
Reexamination Certificate
active
06521842
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of multi-layer circuit boards; more specifically, it relates to multi-layer hybrid surface mount technology (SMT)/pin in hole (PIH) circuit board and a method for soldering a multi-layer hybrid SMT/PIH connector to the board.
BACKGROUND OF THE INVENTION
During assembly of a hybrid SMT/PIH connector to a hybrid SMT/PIH circuit printed circuit board (PCB), two goals must be accomplished. First the SMT connects on the connector must be soldered to the SMT pads on the PCB and second, the pins on the connector must be soldered in the PIHs on the PCB. During rework of a hybrid SMT/PIH printed circuit board (PCB), specifically in the process of removing a hybrid SMT/PIH connector from the board, three goals must be accomplished. First, the proper degree of heat must be maintained to allow the solder securing the SMT connects to the PCB to reach and remain at the solder reflow temperature. Second, the proper degree of heat must be maintained to allow the solder securing the pin connects to the PCB to reach and remain at the solder reflow temperature. Third, it is necessary to prevent the heat applied, especially to the pin connects, from dispersing through the PCB to adjacent components and causing damage to the PCB and components attached thereto. Note that whenever the term PCB is used the more generic term circuit board (CB) may be substituted.
It is common to mount connectors (or active components) to PCBs by inserting pins extending from connectors into plated through holes (PTHs) in the PCB and wave soldering them in place. The PTHs normally provide connections between the pins and conductive planes. Conductive planes may be power planes or signal planes containing signal lines situated at various levels of the PCB. In the case of a connector, the PTHs provide connection to power planes in the PCB. It is also common to mount connectors (or active components) to PCBs using SMT technology using solder paste applied to the SMT pads on the PCB. It is the combination of the two interconnect technologies, SMT and PIH that presents soldering and de-soldering challenges. Hybrid SMT/PIH connectors have hereto been soldered using solder paste applied to the SMT pads as well as filling the PTHs with solder paste.
Particularly challenging is the case where pins must be soldered to PTHs connected to different numbers of power planes in a multi-layer PCB. Heat is normally conducted away from the PTH by the power planes inhibiting the solder from reaching the solder reflow temperature. The more power planes connected to a PTH the more heat is conducted away. Thus, some pins become hotter than other pins during soldering (or some do not become hot enough), and some pins remain cooler than other pins (or some pins become too hot, damaging the PCB) during de-soldering.
Turning to the figures,
FIG. 1
is a partial top view of a related art hybrid SMT/PIH circuit board. In FIG,
1
, PCB
100
is a hybrid SMT/PIN PCB and includes a plurality of SMT pads
105
disposed on a top surface
106
of the PCB. Also formed in PCB
100
are a plurality of PTHs. Three PTHs
110
A,
110
B and
110
C are illustrated. PTH
110
A includes a plated barrel
115
A and a lip
120
A. PTH
110
B includes a plated barrel
115
B and a lip
120
B. PTH
110
C includes a plated barrel
115
C and a lip
120
C. SMT pads
105
and lips
120
A,
120
B and
120
C may be formed by subtractive etching of a copper layer formed on top surface
106
of PCB
100
. Plated barrels
115
A,
115
B and
115
C may be formed by drilling through PCB board
100
and plating the sidewalls of the resulting hole.
FIG. 2
is a partial cross-sectional view of the hybrid SMT/PIH circuit board through line
2
—
2
of FIG.
1
. As may be seen in
FIG. 2
, each of PTHs
110
A,
110
B and
110
C extends from top surface
106
to a bottom surface
112
of PCB
100
. In
FIG. 2
, PCB board
100
is comprised of a plurality of (in this example, twelve) power planes
121
through
132
. Plated barrel
115
A of PTH
110
A is connected to one power plane, power plane
123
. Plated barrel
115
B of PTH
110
B is connected to three power planes; power planes
122
,
125
and
129
. Plated barrel
115
C of PTH
110
C is connected to six power planes; power planes
121
,
124
,
126
,
127
,
130
and
132
. A plurality of signal lines
150
are dispersed between power planes
121
through
132
in a plurality of signal planes
155
. Signal planes
155
are separated from power planes
121
through
132
by dielectric material. In one example the “sandwich” structure of PCB
100
may be formed by etching a signal plane on one side and a power plane on the other side of a printed circuit board joining multiple boards with epoxy or other dielectric adhesive, wherein the dielectric material is epoxy/glass material, fluropolymer, allyated polyphenyl esters, cyanate ester epoxy,( i.e. epoxy, PTFE, or other known dielectric) on one side of signal lines
150
and epoxy or other dielectric adhesive known in the art on the other side of the signal lines.
Also illustrated in
FIG. 2
is a connecter
160
. Connector
160
is a hybrid SMT/PIH connector and includes a plurality of SMT connectors
165
and a plurality (in this example, three) of pins
170
A,
170
B and
170
C. A plurality of SMT connectors
165
are attached to SMT pads
105
by SMT solder joints
175
and pins
170
A,
170
B and
170
C are attached respectively to PTHs
110
A,
110
B, and
110
C by PTH solder joints
180
A,
180
B and
180
C respectively.
FIG. 3
is a partial side view of the hybrid SMT/PIH circuit board of FIG.
1
. In
FIG. 3
, connector
160
, one pair of SMT connectors
165
and one pin
170
are illustrated. SMT connector
165
is attached to SMT pad
105
by SMT solder joint
175
and pin
170
is attached to plated barrel
115
by PTH solder joint
180
.
FIG. 4
is a partial view of power plane
123
through line
4
—
4
of FIG.
2
. SMT pads
105
are shown by dashed lines for reference purposes only and are obviously not present in power plane
123
. In
FIG. 4
, plated barrel
115
A of PTH
110
A is co-extensive with power plane
123
. Each plated barrel
115
B and
115
C of PTH holes
110
B and
110
C are separated from power plane
123
by a gap
185
. Gaps
185
are filled with epoxy or other dielectric adhesive during the assembly pf PCB
100
.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a multi-layer circuit board, comprising: a plurality of conductive planes; a plurality of plated through hole sets, each set comprising one or more plated through holes, none to all of the plated through holes of each set contacting at least one conductive plane; a thermal break formed around each plated through hole in each conductive plane to which the plated through hole is connected; and one or more thermal vents, in the vicinity of each plated through hole in each conductive plane to which the plated through hole is connected.
A second aspect of the present invention is s method of fabricating a multi-layer circuit board, comprising: forming a plurality of conductive planes; forming a plurality of plated through hole sets in at least one of the conductive plane, each set comprising one or more plated through holes, none to all of the plated through holes of each set contacting at least one conductive plane; forming a thermal break around each plated through hole in each conductive plane to which the plated through hole is connected; forming one or more thermal vents, in the vicinity of each plated through hole in each conductive plane to which the plated through hole is connected; placing the conductive planes on top of each other with a dielectric layer located between the conductive planes; and joining the conductive planes together to form the multi-layer circuit board.
A third aspect of the present invention is A method of attaching a hybrid pin in hole/surface mount technology connector or component to a multi-layer circuit board, comprising: providing the hybrid pin in hole/surface mount technol
Brinthaupt, III Mark R.
Jimarez Lisa J.
Wildey William F.
Alcalá José H.
Fraley Lawrence R.
International Business Machines - Corporation
Paladini Albert W.
Schmeiser Olsen & Watts
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