Data processing: generic control systems or specific application – Specific application – apparatus or process – Specific application of temperature responsive control system
Reexamination Certificate
1998-07-16
2001-08-14
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Specific application of temperature responsive control system
C700S121000, C700S299000, C374S011000, C374S014000
Reexamination Certificate
active
06275750
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to Japanese applications Nos. HEI 9(1997)-194177, filed on Jul. 18, 1997, HEI 9(1997)-313681, filed on Nov. 14, 1997, and HEI 10(1998)-119423, filed on Apr. 28, 1998, whose priorities are claimed under 35 USC § 119, the disclosures of which are incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for setting heating conditions in a heating furnace and a thermal analyzer for an object to be heated in the heating furnace. More particularly, the present invention relates to an apparatus for setting heating conditions which is to be suitably used for control of a reflow furnace for heating a printed-wiring board to perform soldering, for example, which is to be suitably used when heating the printed-wiring board in the reflow furnace, and a thermal analyzer for the printed-wiring board which is suitably used when setting the heating conditions.
2. Description of the Related Art
A printed-wiring board having electronic components mounted thereon (which is also referred to as a circuit substrate, a printed board, a printed substrate or the like) is usually manufactured by a process of printing a creamy soldering material (soldering paste) onto the printed-wiring board, mounting the electronic components thereon, and putting them into a reflow furnace (which is also referred to as a reflow soldering apparatus or a reflow apparatus) to perform reflow soldering.
In this process, the printed-wiring board is put on a conveyer provided in a tunnel-shaped furnace and is carried. At the carrying step, the printed-wiring board is heated by a heating source provided in the furnace, the soldering paste is melted with an increase in a temperature of the printed-wiring board, is then carried to the outside of the furnace and exposed to room temperature for cooling. Consequently, the solder is solidified. Thus, soldering is completed.
In the reflow soldering process, the printed-wiring board is heated to a temperature of 200° C. or more at which the solder is melted. In that case, heating control is performed in such a manner that a temperature profile becomes a curve shown in a graph of FIG.
5
. In order to lessen thermal damages caused by rapid heating, a temperature is not simply raised but preheating is performed. Then, uniform heating is performed to hold the temperature of the printed-wiring board constant. Thereafter, heating is performed to a temperature of 200° C. or more at which the solder is melted. Thus, heating control is performed in three stages.
However, a plurality of components having various heat capacities are generally mounted on the printed-wiring board so that the temperature is varied on the printed-wiring board. Therefore, it is very hard to set heating conditions that the printed-wiring board is heated enough to melt the solder and that temperatures of small components are not raised too much. For this reason, a plurality of heating sources having different properties are provided in the reflow furnace to vary the influence of the heating source depending on a position of the printed-wiring board. More specifically, a plurality of near-infrared radiation heaters and a plurality of far-infrared radiation heaters or a plurality of hot air fan heaters whose temperatures are kept different are provided above and below the conveyer so that a heating zone is divided into plural portions. Heating conditions of the heating source in each heating zone are properly set respectively to heat the printed-wiring board in such a manner that a temperature difference of the printed-wiring board is reduced as much as possible and a temperature distribution of the printed-wiring board is uniform.
For this reason, conventionally, a temperature sensor such as a thermoelectric couple has been attached to the printed-wiring board to measure a rise in the temperature of the printed-wiring board, and temperature setting has been changed repeatedly until a target temperature profile is obtained.
However, a work for changing the temperature setting is performed by a worker's perception or guess. Therefore, there is no assurance that optimum heating conditions can be set. Furthermore, the heating conditions are repeatedly set and the temperature of the printed-wiring board is repeatedly measured to find the optimum conditions. Consequently, plenty of time is required to set the optimum heating conditions, and the worker's skill and experience are necessary.
In a case where the heating conditions in the reflow furnace are not suitable, for example, the printed-wiring board is heated too much, a thermal stress is easily applied to small chip components having small thermal capacities and the printed-wiring board. Conversely, in a case where the heating is insufficient, solder joint portions of large components having great thermal capacities are unmelted.
For a printed-wiring board to be newly manufactured, therefore, it is necessary to find optimum heating operation conditions for the reflow furnace in which a thermal stress applied to the components and the printed-wiring board is lessened as much as possible and solder joint portions can fully be heated. For each solder joint portion on the printed-wiring board, a temperature profile should be examined in detail.
This examination is performed by repeatedly, several times, acquiring the temperature profile of the printed-wiring board (by measuring the same temperature profile by means of a thermoelectric couple) and resetting heating conditions such as a heater temperature and the like. For this reason, a lot of man-day is required to fix the thermoelectric couple and to measure the temperature profile plural times. Furthermore, every time the heating conditions are changed, plenty of time is taken to stabilize the heater temperature, that is, considerable man-day and time are required. In addition, the worker's experience and accumulation of know-how are important in order to predict the optimum heating conditions based on a result of the measurement of the temperature profile.
Therefore, the following has been investigated. Thermal analysis is performed by using a computer to quantitatively grasp a heating state in the reflow furnace in order to enhance reliability of the printed-wiring board. Moreover, the temperature profile of a heated object in the reflow furnace is predicted and utilized for setting the optimum operation conditions in the reflow furnace.
FIG. 10
is a flowchart showing a processing of performing thermal analysis for the printed-wiring board in the reflow furnace using the prior art.
At Steps
501
to
507
, an analytic model of the printed-wiring board is first generated in order to perform the thermal analysis for the printed-wiring board. On the printed-wiring board are mounted electronic components having several hundred or more junction terminals such as lead frames having fine and complicated shapes which are referred to as a QFP (Quad Flat Package), a SOP (Small Outline Package), a BGA (Ball Grid Array) and the like.
At the Step
501
, a method for simplifying such an analytic model of the electronic component is examined in order to shorten a computation time or to reduce man-day for creating the analytic model. It is necessary to simplify the analytic model without reducing computation precision. To perform the simplification, technical knowledge and experience are required.
Next, the analytic model of the component is created at Step
502
based on a result of the examination of the simplifying method (the Step
501
) At Step
503
, a physical property value is defined for the created analytic model of the component.
In general, a plurality of electronic components are mounted on the printed-wiring board. Therefore, a work for simplifying the analytic model of the component (the Step
501
) and a shape forming work (the Step
502
) are performed for each component (Step
504
).
At the end of the work for creating the analytic model, the sha
Sakuyama Seiki
Uchida Hiroki
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Grant William
Rodriguez Paul
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