Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-11-30
2003-07-15
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S388000, C219S400000, C219S526000, C219S536000, C228S222000, C228S223000
Reexamination Certificate
active
06593549
ABSTRACT:
FIELD OF THE INVENTION
The present application relates to reflow ovens and, in particular, cooling components used in reflow ovens.
BACKGROUND OF THE INVENTION
Reflow ovens are used in the manufacture of printed circuit boards (“PCBs”) and other electronic devices, where electrical components are connected to the PCB and to each other by solder. In one step of a typical process for manufacturing a PCB, for example, a central processing unit (“CPU”) is connected to an interposer or substrate by placing solder paste on the interposer at the desired location for the CPU and placing the CPU onto the solder. The interposer is then placed on a conveyor belt that carries the substrate through the reflow oven. The reflow oven includes a heating section, where heat is generated to melt the solder, and a cooling section to cool and harden the solder, connecting the CPU to the PCB. An example of a reflow oven is the ATMOS 2000CR™ Reflow Oven, available from Electrovert®, Camdenton, Mo.
In the ATMOS 2000CR™ Reflow Oven, cooling gas is provided to three cooling devices that emit the gas onto the PCB. The cooling devices in the ATMOS 2000CR are multi-piece elongated members including an internal longitudinal cavity and a longitudinal slit. Compressed gas is provided to the internal cavity and emitted through the slit in the form of a high velocity laminar flow onto the PCB's as they are carried by the conveyor.
FIG. 1
is a perspective view of a portion of a cooling device
10
used in the ATMOS 2000CR. Compressed gas is provided to the internal cavity of the cooling device
10
from a side of the device through a tube
11
a
and an adapter
11
b
. The gas is emitted through a longitudinal slit (not shown) on the PCBs. The cooling device
10
in the ATMOS 2000CR™ Reflow Oven is an Air Knife™ available from Exair Corporation, Cincinnati, Ohio.
Solder paste includes a deoxifying agent, referred to as flux, to remove oxides from the surfaces of the components to be soldered together. The flux typically becomes a vapor at a temperature below the temperature of the heating section and circulates throughout the oven. The vapor condenses on the cooling devices in the ATMOS 2000CR Reflow Oven, clogging the longitudinal slits through which the cooling gas exits the cooling devices. A heater
12
is therefore provided in contact with the cooling device
10
to heat the cooling device and melt the flux during periodic cleaning of the oven. The heater
12
is held against the cooling device
10
by two clips
14
that are bolted to each cooling device
10
through a hole
14
a
.
FIG. 1
shows one such clip
14
. The clip
14
has a 90° bend
15
and a straight portion
16
that bears against the heater
12
, pressing the heater
12
against the cooling device
10
. A lip
18
extends perpendicular to the straight portion
16
, adjacent to a side of the heater
12
, as shown in the rear perspective view of FIG.
2
and in FIG.
3
. The clip
14
is formed of a layer of spring steel having a thickness of about 0.889 mm. When connected within the ATMOS 2000CR™ Reflow Oven, the assembly of the cooling device
10
, the heater
12
and the clip
14
, as shown in
FIG. 1
, is rotated 180° about a longitudinal axis of the cooling device in
FIG. 1
so that the heater is below the cooling device.
The inventor has found that over time the clip
14
may weaken, allowing the heater
12
to separate from the cooling device
10
. The cooling device
10
may not, therefore, reach the optimal temperature for melting the flux, typically 200° C. The cooling device
10
may then stay clogged, interfering with its ability to exhaust a sufficient quantity of cooling air to cool the PCB.
In the ATMOS 2000CR™ Reflow Oven, thermocouplesare provided on each of the cooling devices. The duty cycles of the heaters
12
on all three cooling devices
10
are controlled by software based on the temperature sensed by the thermocouple on the middle of the three cooling devices
10
. The inventor has also found that the heaters
12
may be turned off before the cooling device
10
closest to the exit reaches the optimal temperature for cleaning.
REFERENCES:
patent: 5577658 (1996-11-01), Bailey et al.
patent: 5611476 (1997-03-01), Soderlund et al.
patent: 5993500 (1999-11-01), Bailey et al.
patent: 6120585 (2000-09-01), Inomata et al.
patent: 2753921 (1998-04-01), None
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Pelham Joseph
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