JPH0555738A - Electronic parts mounting method - Google Patents

Abstract

PURPOSE:To eliminate unsoldered areas to enhance reliability of electrical connection in an electronic parts mounting method for soldering electronic parts on a printed circuit board. CONSTITUTION:Sufficient quantity of solder is acquired at the time of soldering within a reflow surface and reliability of electrical connection is enhanced by eliminating unsoldered areas with a reflow soldering method conducted after flatness for a printed circuit board of leads of electronic parts grounded to the printed circuit board is detected, quantity of solder is increased by precedingly applying or transferring cream solder to the floating leads floated more than thickness of the cream solder printed on the printed circuit board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic component mounting method for mounting electronic components on a printed circuit board with high reliability.

[0002]

2. Description of the Related Art In recent years, electronic devices are becoming smaller and more multifunctional, and a variety of surface mounting electronic components are becoming available. For example, I with leads in four directions called QFP
In C, the pitch between leads is 0.5 mm or less and exceeds 300 pins, and the flatness of the grounding portion of the lead when mounted on the printed circuit board is 0 due to the difficulty of processing and the limit of the inspection and correction process. It is extremely difficult to go below 0.1 mm.

Further, from the viewpoint of increasing the number of functions, various types of electronic parts called atypical parts having special functions that cannot be mass-produced are available on the market. These parts are manufactured
Since the processing process is special, it is difficult to keep the flatness of the leads grounded to the printed circuit board within a certain range.

A conventional electronic component mounting method will be described below. As shown in FIG. 3, the cream solder is printed on the printed circuit board by screen printing. At this time, the printing thickness of the cream solder is generally 150 μm to 200 μm.
Before and after, for example, when there is a minute chip component called 1005 or IC mounting with a narrow pitch, there is a printing thickness of around 100 μm in order to prevent excessive soldering during soldering. Further, the screen is generally a thin plate or a mesh, and it is extremely difficult to arbitrarily set the printing thickness on the same printed circuit board.

After that, electronic parts are mounted on the printed circuit board on which the cream solder is printed. Then, it is put into a reflow furnace to melt the solder and complete soldering.

[0006]

However, the above-mentioned conventional method has a problem that the printed thickness of the cream solder is thinned and the unsoldered portion at the time of soldering is increased, resulting in poor electrical connection. Was there.

There is also an electronic component mounter configured to detect the flatness of the leads of the electronic component and not mount the lead outside the allowable range, but the electronic component not mounted is again inspected and manually corrected. There is a problem that the above process is required and labor is required, and further, in the case of an IC having a narrow pitch, it is not only difficult to manually correct the IC, but also the normal lead is lost in the correction process.

The present invention solves the above-mentioned conventional problems by ensuring a sufficient amount of solder when soldering in a reflow furnace,
It is an object of the present invention to provide an electronic component mounting method that eliminates unsoldered portions and improves reliability of electrical connection.

[0009]

In order to achieve this object, an electronic component mounting method of the present invention is a method of applying or transferring cream solder to a lead portion of an electronic component to increase the amount of solder.

[0010]

By this method, it is possible to secure a necessary amount of solder at the time of soldering in the reflow furnace even for the lead portion of the electronic component in which the flatness of the ground plane is not sufficiently ensured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, after the printed circuit board is put into a mounting machine, cream solder is printed on the printed circuit board by screen printing.

Then, before mounting the electronic component 2 on the printed circuit board, the flatness of the lead of the electronic component 2 grounded to the printed circuit board with respect to the printed circuit board is measured using, for example, a laser detector, and the printed thickness of the cream solder is measured. The presence or absence of the floating lead is detected.

As for the floating lead 3 which exceeds the allowable range as a result of detection, the cream solder 5 is applied to the ground surface of the floating lead 3 by the dispenser 4, and the floating lead 3 is grounded when the floating lead 3 is grounded to the printed circuit board. 3 and the printed circuit board are filled with the cream solder 5 applied. When the flatness of the lead is within the allowable range and there is no floating lead 3, the lead of the electronic component 2 is mounted on the printed circuit board as it is.

When there are a plurality of electronic parts, the above steps are repeated. The printed circuit board on which the electronic components have been mounted is placed in a reflow furnace to melt the solder and complete soldering.

As described above, according to this embodiment, the cream solder 5 is applied by the dispenser 4 to the ground surface of the floating lead 3 having a printing thickness greater than the printing thickness of the cream solder applied to the printed circuit board by the screen printing. Can dramatically improve the soldering reliability of electronic components that have leads whose flatness has not been ensured, which can only be corrected and corrected manually, and improve the quality and mass productivity of electronic devices. We can improve together.

Instead of the application by the dispenser 4 described above, it is also possible to transfer a certain amount of cream solder to the lead portion of the electronic component.

When it is difficult to directly apply or transfer the cream solder to the leads, it is also possible to apply, transfer or draw the cream solder to the grounding surface side of the printed circuit board with the leads.

Further, when it is necessary to increase the amount of cream solder regardless of the floating amount of the leads, it is also possible to apply or draw a certain amount of the cream solder on the leads or the printed circuit board without detecting the floating of the leads.

[0020]

As is apparent from the above description of the embodiments, the present invention uses a method in which cream solder is applied or transferred in advance to the lead portion of an electronic component to increase the amount of solder. It is possible to realize an excellent electronic component mounting method that secures a sufficient amount of solder at the time of soldering and eliminates unsoldered portions to improve reliability of electrical connection.

[Brief description of drawings]

FIG. 1 is a flowchart of an electronic component mounting method according to an embodiment of the present invention.

FIG. 2 is an external perspective view showing the concept of a cream solder applying method of the electronic component mounting method.

FIG. 3 is a flowchart of a conventional electronic component mounting method.

[Explanation of symbols]

 2 Electronic parts 3 Floating lead 5 Cream solder

Claims (2)

[Claims] 1. A method of soldering an electronic component onto a printed circuit board, the flatness of a lead of the electronic component grounded to the printed circuit board to the printed circuit board being detected,
An electronic component mounting method in which cream solder is applied or transferred in advance to floating leads floating above the thickness of cream solder printed on the printed circuit board to increase the amount of solder and then reflow soldering. 2. The electronic component mounting method according to claim 1, wherein the lead is applied or transferred with a solder amount corresponding to the flatness of the lead.