JPH04270063A - Heat conduction reflow soldering apparatus - Google Patents

Abstract

PURPOSE:To secure joint strength in a soldered joint formed on the surface of a mounted substrate. CONSTITUTION:Heater block 11 for preheating, heater block 12 for reflow, heater block 21 for adjusting cooling speed of the substrate and block 13 for cooling the substrate, are set. While conveying the parts-mounted substrate P with an endless belt 16 arranged between pulleys 14, 15, the substrate P is heated with the heater blocks 11, 12 through the conveying belt 16. On the heater block 12 for reflow, solder paste applied between the substrate and the mounted parts is melted. In the heater block 21 for adjusting the cooling speed of substrate, the substrate is adjusted by heating it with a little quantity of heat so as to lower the cooling speed of the aluminum substrate having good thermal conductivity. At the time of forming the soldered joint by solidifying molten solder between the substrate and the mounted parts, the cooling speed at the substrate side is sided with the cooling speed at the parts side of this soldered joint with the above heating adjustment. The development of internal stress due to imbalance of temp. distribution in the soldered joint is restrained.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer reflow soldering apparatus mainly suitable for heat transfer reflow soldering of workpieces having good thermal conductivity (eg, component-mounted aluminum substrates, ceramic substrates).

0003

2. Description of the Related Art As shown in FIG. 3, a conventional heat transfer reflow soldering apparatus has a reflow heater block 12 disposed downstream of a plurality of preheat heater blocks 11. A workpiece cooling block 13 is arranged on the downstream side. Furthermore, a workpiece conveyance belt 16 is wound endlessly from the pulley 14 at one end to the pulley 15 at the other end. By moving this work conveying belt 16 around the upper surface of each block 11, 12, 13, each heater block 11, 12 is transmitted to the workpiece P through the conveyor belt 16, and the workpiece P is forcibly cooled through the conveyor belt 16 by the workpiece cooling block 13.

As shown in FIG. 4, the temperature profile of the workpiece (component mounting board) P is such that the workpiece P is preheated at a relatively low temperature of 180° C. or less on the plurality of preheating heater blocks 11. On the reflow heater block 12, the workpiece P is heated to a high temperature of 210° C. or higher to melt the solder paste applied to the workpiece P. The workpiece P that has passed through the reflow heater block 12 is heated to 150°C in a short time by the cooling plate that is air-cooled in the workpiece cooling block 13.
cooled down to below. As a result, the molten solder is solidified, and a solder joint portion is formed between the board and the mounted component to electrically connect them.

[0005]

[Problems to be Solved by the Invention] As described above, in the conventional heat transfer reflow soldering apparatus in which the molten solder reflowed on the reflow heater block 12 is cooled all at once by the workpiece cooling block 13, the workpiece P is When a board with good heat capacity (aluminum board, etc.) and components mounted on the board have a large heat capacity, the solder joint formed between them will cause a rapid temperature drop on the component side compared to a rapid temperature drop on the board side (cooling plate side). This has the disadvantage that the speed is not high enough, and a significant imbalance in temperature distribution occurs in the solder joint, causing internal stress in the solder joint, which affects the strength of the joint.

[0006] The present invention was developed in view of the above-mentioned problems, and the present invention has been developed to solve the problem of solder joints formed between a board with good thermal conductivity and a mounting component with a large heat capacity in a heat transfer reflow soldering device. The purpose of this is to minimize the influence of internal stress on joint strength.

[Configuration of the invention]

[0008]

[Means for Solving the Problems] The present invention provides a method for moving the workpiece P from the reflow heater block 12 while transporting the workpiece P.
In a heat transfer reflow soldering device that performs reflow soldering using heat conducted to the reflow soldering device, a workpiece cooling rate adjusting heater block 21 is disposed downstream of the reflow heater block 12.

[0009]

[Operation] In the present invention, after reflow soldering is performed by heat conducted from the reflow heater block 12 to the workpiece P, the cooling rate of the workpiece P is adjusted by the workpiece cooling rate adjusting heater block 21, and the solder joint is cooling slowly to avoid significant imbalances in temperature distribution,
Suppresses the generation of internal stress in solder joints.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2.

As shown in FIG. 1, a reflow heater block 12 is arranged downstream of a plurality of preheat heater blocks 11.
A heater block 21 for adjusting the workpiece cooling rate is arranged on the downstream side of the heater block 21 for adjusting the workpiece cooling rate.
A workpiece cooling block 13 is arranged downstream of the workpiece.

[0012] The plurality of preheating heater blocks 1
The temperature of each of the reflow heater block 1 and the reflow heater block 12 can be controlled individually. The workpiece cooling rate adjustment heater block 21 is the preheating heater block 1.
This is a temperature controllable heater block formed to the same dimensions as 1. The workpiece cooling block 13 includes an air-cooled cooling plate on the workpiece transfer surface.

Further, a workpiece conveyance belt 16 is wound endlessly from the pulley 14 at one end to the pulley 15 at the other end. By transporting the upper rotating part of this workpiece conveyance belt 16 through the upper surface of each block 11, 12, 21, 13, while conveying the workpiece (component mounting board) P placed on this belt 16, Each heater block 11, 12
, 21 is conducted to the workpiece P through the conveyor belt 16, or the workpiece P is forcibly cooled through the conveyor belt 16 by the workpiece cooling block 13.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIG. 2.
Above, the workpiece P is gradually heated through the conveyor belt 16 and preheated at a relatively low temperature of 180° C. or less.

On the reflow heater block 12, the reflow heater block 1 whose preset temperature is set to a high temperature is placed on the reflow heater block 12.
A large amount of heat is conducted from 2 to the workpiece P through the conveyor belt 16, and the workpiece P is heated to a high temperature of 210° C. or more, melting the solder paste applied to the workpiece (between the board and the mounted component).

The workpiece P heated to the reflow temperature in this way is heated to the workpiece cooling rate adjusting heater block 2.
1, the heater block 21 is heated by a small amount of heat so as to slow down the cooling speed of the workpiece, especially for components mounted on a board with a large heat capacity, such as an aluminum board with good thermal conductivity. So 18
It is slowly cooled at a rate that does not drop below 0°C. By controlling the temperature of the heater block 21, an arbitrary cooling rate can be obtained.

Therefore, at the initial stage when the molten solder between the board and the mounted component solidifies and a solder joint is formed, the rate of temperature drop on the board side of the solder joint and the rate of temperature drop on the component side are different. As a result, the temperature distribution in the solder joint does not become significantly unbalanced, so that the generation of internal stress in the solder joint can be suppressed.

Heater block 21 for adjusting workpiece cooling speed
The workpiece P that has passed through the workpiece cooling block 13 cools the workpiece P in a short time to 150% by cooling plate which is air-cooled.
It is rapidly cooled to below ℃.

[0019]

[Effects of the Invention] According to the present invention, in the heat transfer reflow soldering apparatus, since the workpiece cooling rate adjusting heater block is disposed downstream of the reflow heater block,
Even when the workpiece consists of a board with good thermal conductivity and a mounted component with a large heat capacity, the workpiece cooling rate adjustment heater block can adjust the cooling rate of the workpiece to create a cooling gap between the board and the component. Cool slowly so that there is no significant imbalance in the temperature distribution of the solder joint.
The generation of internal stress in the solder joint can be suppressed. In addition, reduction in joint strength due to internal stress can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of a heat transfer reflow soldering apparatus of the present invention.

FIG. 2 is a graph showing a temperature profile of the heat transfer reflow soldering device same as above.

FIG. 3 is a plan view showing a conventional heat transfer reflow soldering apparatus.

FIG. 4 is a graph showing a temperature profile of the conventional heat transfer reflow soldering apparatus same as above.

[Explanation of symbols]

P Work

Claims (1)

[Claims] 1. In an apparatus that performs reflow soldering using heat conducted from a reflow heater block to the workpiece while transporting the workpiece, a heater block for adjusting the cooling rate of the workpiece is disposed downstream of the reflow heater block. A heat transfer reflow soldering device featuring: