Metal fusion bonding – Process – Plural joints
Reexamination Certificate
2000-08-04
2002-06-11
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Plural joints
C228S200000, C228S046000, C432S010000
Reexamination Certificate
active
06402011
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a reflow method and reflow device wherein, by heating a printed circuit board on which electronic components are loaded and to which solder cream has been applied at locations to be connected, solder is melted and electronic components soldered.
BACKGROUND ART
A variety of methods for reflow soldering technology to mount electronic components on printed circuit boards are already known. These methods include, for example, batch reflow soldering of surface mount components, local soldering of insert mount components after batch reflow soldering of surface mount components, and local reflow soldering of surface mount components and insert mount components.
A conventional reflow device for batch reflow soldering of surface mount components is constituted so as to melt solder and to solder electronic components by uniformly heating a printed circuit board with the radiant heat of a panel heater and hot air heated to a prescribed temperature.
Also, the reflow device according to the report of Japanese Patent Publication No. 7-73790 is an example of a reflow device for local heating and reflow of surface mount components and insert mount components. As shown in
FIG. 11
, this reflow device (
50
) is equipped with the following: hot air chamber (
53
) installed on the lower side of the transport path (
52
) for the printed circuit board (
51
) which collects gas heated to a temperature at which solder cream melts, an upper plate (
57
) installed to cover the opening section (
54
) of the hot air chamber (
53
) and in which is formed a plurality of hot air blow holes (
56
) to blow the hot air (
55
) selectively on only the necessary sections of the printed circuit board (
51
), and means for transport (
58
) to supply and remove the printed circuit board (
51
).
Because heating is local, this reflow device (
50
) makes possible the following processes: sectional soldering, soldering of components with low heat resistance, and concurrent soldering of lead components (
59
) and chip components (
60
) wherein the lead terminals protrude from the lower surface of the board.
However, batch reflow soldering is not possible when using the aforementioned, conventional type of reflow device if electronic components with low heat resistance are present together on a printed circuit board. Those components with low heat resistance among the electronic components will be damaged if that printed circuit board undergoes batch reflow soldering with the reflow device; therefore, the components with low heat resistance among the electronic components must be soldered separately, resulting in the problem of decreased productivity of the mounting process.
Meanwhile, the reflow device (
50
) shown in
FIG. 11
makes possible batch soldering for a printed circuit board (
51
) on which electronic components with low heat resistance are present together by locally blowing hot air without blowing the hot air to the locations of the electronic components with low heat resistance.
Actually, batch soldering of the electronic components (lead component (
59
) and chip component (
60
), etc.) placed on the entire surface of the printed circuit board (
51
) is not possible for the following reason. In effect, reflow soldering electronic components such as lead component (
59
) and chip component (
60
), etc., with the reflow device (
50
) requires heating to temperatures in the vicinity of 230° C. for 20-30 seconds. Hot air of a temperature of roughly 350° C. or greater is necessary to ensure the quantity of heat necessary for that purpose. In hot air of such high temperatures, areas of the printed circuit board (
51
) in which the temperature rises easily reach temperatures approaching that of the hot air. Even heat resistant components (for example, the temperature of heat resistance for QFP is 250° C. (QFP is heat resistant to temperatures of 250° C.) cannot withstand that temperature. When the hot air temperature is reduced to 250° C., the temperature of heat resistance, in order to avoid [damage], the risk is that areas of the printed circuit board (
51
) in which the temperature rises with difficulty are not heated to the temperatures necessary for soldering within a prescribed period of time and high reliability soldering may not result.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a reflow method and reflow device which resolve the problems and make possible batch soldering with high reliability and without resulting in heat damage to electronic components on the printed circuit board.
In order to solve the problems, the reflow method of the present invention is a reflow soldering method in which hot air is blown locally and roughly perpendicular to locations to be connected on one surface of a printed circuit board, concurrent with radiant heating of the surface of a printed circuit board, on which electronic components are loaded and to which solder cream has been applied at locations to be connected.
This reflow method permits secure soldering in such a manner that the temperature of the hot air does not exceed the temperature of heat resistance of the electronic components because of its combination with the radiant heat. Moreover, this reflow method can permit soldering in such a manner that only those points to be connected are heated selectively because the hot air is blown locally and roughly perpendicular to the points to be connected. This reflow method prevents heat damage to sections other than the points to be connected and ensures that the solder at the points to be connected is melted.
Additionally, the reflow method of the present invention permits batch reflow soldering of electronic components, on a printed circuit board to which solder cream is applied, because the surface to undergo reflow soldering of the printed circuit board is heated while the components with low heat resistance, among the electronic components on the printed circuit board, are cooled.
Since reflow soldering is performed while the components with low heat resistance among the electronic components are cooled, this reflow method can prevent damage to the components with low heat resistance among the electronic components and can perform batch reflow soldering of electronic components on a printed circuit board. Consequently, performing reflow soldering for operations conducted with conventional flow dip soldering improves soldering quality. In effect, the flow method results in a two-time heat history since the printed circuit board passes through the flow device after passing through a curing oven in order for temporary affixation of surface mount components with adhesive. However, in the method of the present invention, the board needs to only pass once through the reflow device. This results in a one time heat history and prevents deterioration of the capacity of the electronic components. Also, when surface mount electronic components are placed on both surfaces of the printed circuit board, points to be connected of the electronic components on the lower surface are cooled during reflow; therefore, those electronic components will not drop off even if they are not affixed with adhesive. Consequently, the process for applying adhesive when the surface mount electronic components are placed thereon can be eliminated.
Also, in the aforementioned reflow method, the electronic components placed on the printed circuit board include surface mount components and insert mount components. The present invention permits batch reflow soldering of these surface mount components and insert mount components.
This reflow method makes possible reflow soldering of lead insert mount components which before now could not pass through a reflow device which heats the entire board. Consequently, production costs do not rise because insert mount components can be used without further processing.
Also, in the aforementioned reflow method, the present invention heats one surface of the printed circuit board while cooling the other surface of the
Ishimoto Kazumi
Kitagawa Tatsuaki
Matsushima Osamu
Nagai Koichi
Nemoto Seizo
Dunn Tom
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Stoner Kiley
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