JPH01271094A - Paste-like solder - Google Patents

Abstract

PURPOSE:To eradicate the Manhattan phenomenon of a face packaging part by using the paste-like solder composed of two kinds of solder grains of different m.p. CONSTITUTION:A paste-like solder 10 is composed by mixing at specified amt. the low m.p. solder grain 10a having the m.p. difference of about >=20-30 deg.C and a high m.p. solder grain 10b. A face packaging part 1 is lightly joined to conductive layers 6, 7 by the low m.p. solder grain 10a first. In this case there is a difference of elevation in an atmospheric temp. and at the time when the part of the conductive layer 6 side is higher only the low m.p. solder grain 10a there is melted. Due to the surface tension generated at that time being small and no moment enough to rise the conductive layer 7 of one part being unobtainable a Manhattan phenomenon is not caused. With further rise of the atm. temp. the high m.p. solder grain 10b is also melted and completely fixed without causing the Manhattan phenomenon via the same trend process as the low m.p. solder grain 10a. Consequently, the Manhattan phenomenon of the face packaging part can surely be eradicated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a paste-like solder suitable for use when attaching surface-mounted electronic components to a printed circuit board using a reflow soldering device or the like. .

[Prior art] In order to increase the packaging density of hybrid ICs, etc., there is a tendency to use surface-mounted electronic components that are light, thin, short, and small, such as chip-type capacitors, for electronic components mounted on IC boards. .

Further, there are various thicknesses of surface mount components, and even the same electronic component has various sizes.

To mount such surface-mounted components, reflow soldering equipment is often used.

As shown in FIG. 4, the surface mount component 1 is temporarily fixed between the conductive layers 6, 7 formed on a predetermined printed circuit board 5 using paste solder 8, 9, etc. Then, the printed circuit board 5 is transported into a reflow oven (not shown).

As the paste solder 8.9, for example, 5n-pb eutectic solder (its melting point is 183° C.) is used.

As the printed circuit board 5 passes through a high temperature atmosphere (183°C or higher) in the reflow oven, the paste solder 8
．． 9 is melted, and the printed circuit board 5 is cooled by subsequent transportation. The melted solder is now solidified, and the surface mount component 1 is completely fixed on the printed circuit board 5.

[Problems to be Solved by the Invention] By the way, as mentioned above, when reflow soldering uses a device to mount the surface mount component 1 on the printed circuit board 5, reflow soldering requires the use of a high-temperature atmosphere inside the device. Not all the surface-mounted components 1 passing through always exhibit a negative temperature distribution.

The shapes and sizes of electronic components to be mounted vary, and small surface-mounted components are affected by the large surface-mounted components, and This is because a temperature difference may occur even between the left and right electrode portions.

If there is a difference in temperature like this, the paste solder 8
.

In this way, for example, if the paste solder 8 on the left side is completely melted and the paste solder 9 on the right side is incompletely melted, the completely melted paste solder 8 side is more likely to melt than the other paste solder 8 itself. surface tension increases.

This surface tension difference, as shown by the arrows in Figure 4,
．． This appears as a difference in the moment (vertical component of the rotational moment) in the height direction at 4, and the moment applied to the electrode part 3 on the completely melted side is greater than the moment applied to the incompletely melted electrode part 4 side. The mountain crab grows big.

This causes the so-called Manhattan phenomenon in which the surface-mounted component 1 stands up as shown in FIG. 5.

The smaller the component, the greater the surface tension of the solder relative to the component's own weight, making the Manhattan phenomenon more likely to occur.

In today's electronic components, there is a tendency to make the components themselves smaller in order to improve the packaging density, and therefore the Manhattan phenomenon is likely to occur.

Further, in the vapor phase soldering method (VPS method) which has been developed in recent years, the Manhattan phenomenon is particularly likely to occur, which is a big problem.

Bonding failure due to the Manhattan phenomenon is a factor that significantly reduces the yield and reliability of reflow soldering.

In order to prevent the Manhattan phenomenon and eliminate soldering defects, it is conceivable to use an adhesive 14 to prevent the surface mount component 1 from rising as shown in FIG.

However, if this adhesive 14 is used, when the surface mount component 1 is misplaced as shown in FIG. 7, it will be soldered in a misaligned state.

This may lead to accidents such as contact with other electronic components, so it cannot be said to be a very good solution.

If adhesive is not used, even if the component is placed misaligned, a horizontal moment (arrow) due to the molten solder will act on the surface mount component 1 as shown in FIG. 8A. A direction correction force (self-alignment) acts on the surface mount component 1.

As a result, it is fixed at the normal position as shown in FIG.

If adhesive 14 is used, the self-alignment effect of the molten solder cannot be utilized.

Therefore, the present invention proposes a paste-like solder that does not cause such rising phenomenon of surface-mounted components, and is extremely suitable for application to the above-mentioned board device.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides that at least two types of solder grains having different melting points are mixed in predetermined amounts to form a paste. It is.

[Function] Low melting point solder grains 10a (lla) and high melting point solder grains 1
When using solder mixed with 0b (llb),
First, the surface mount component 1 is lightly bonded to the conductive layer 6.7 using the low melting point solder grains 10a.

In this case, when there is a difference in atmospheric temperature and the temperature on the conductive layer 6 side is higher, only the low melting point solder grains 10a on the conductive layer 6 side melt.

However, in this case, the Manhattan phenomenon does not occur. This is because the surface tension generated by the melting of the low melting point solder grains 10a (lla) is small, so that a moment sufficient to cause one side of the surface mount component 1 (the side of the conductive layer 7) cannot be obtained.

As time passes, the low melting point solder grains 11a on the other conductive layer 7 side also melt, thereby causing the electrodes 3.
4 are both lightly bonded to the conductive layer 6.7.

When the ambient temperature rises rapidly, the high melting point solder grains also melt. At this time, if there is a difference in ambient temperature and the temperature is higher on the conductive layer 6 side, the high melting point solder grains 10b on the conductive layer 6 side melt first.

However, even in this case, since the conductive layer 7 side is lightly bonded by the low melting point solder grains 11a, the conductive layer 7 side
The surface mount component 1 does not rise due to the moment generated by the melting of the high melting point solder grains 10b on the side. In other words, the Manhattan phenomenon does not occur.

[Embodiment] Next, a case in which an example of the paste solder according to the present invention is applied to soldering of the above-mentioned surface-mounted electronic component will be described in detail with reference to FIG. 1 and subsequent figures.

Also in this invention, as shown in FIG. 1, a surface mount component 1 placed on predetermined conductive layers 6 and 7 formed on a printed circuit board 5 is fixed with paste solder 10 and 11. Ru. This constitutes a substrate device.

In this invention, a special solder as shown below is used as the paste solder for joining the surface-mounted components 1.

That is, in this invention, as shown in FIG.
Low melting point solder grains 10a (lla) and high melting point solder grains 10
Paste solder 10 mixed with a predetermined amount of b (llb)
(11) is used.

In this case, the temperature difference between the two (difference in each melting point) is at least 5
A solder having a temperature of 20 to 30° C. or higher can be selected.

For example, as the low melting point solder grains 10a, the melting point is 150°C.
When using solder grains (a ternary alloy or a quaternary alloy containing bismuth), a 5n-pb type solder having a melting point of 183° C. is used as the high melting point solder grains 10b.

As the low melting point solder grains 10a actually used, solder grains having a melting point within the range of 130 to 170°C are suitable. Similarly, as the high melting point solder grains 10b, solder grains whose melting point is within the range of 150 to 210°C are suitable (the particle size of the solder grains is about 10 μm to 50 μm).

).

Now, solder grains 10a having such a temperature difference in melting point,
10b are mixed to form a paste as shown in FIG.

The mixing ratio is, for example, 30% of the low melting point solder grains 10a.
The high melting point solder grains 10b account for about 70% by weight.

The reason why the weight percentage of the low melting point solder grains 10a is smaller than that of the high melting point solder grains 10b is because the low melting point solder grains 1
This is because the purpose of 0a is achieved if the surface-mounted components 1 can be lightly bonded while suppressing the Manhattan effect of the surface-mounted components 1. Therefore, the above-mentioned mixing ratio and melting point of solder are only examples.

When the surface mount component 1 is soldered as shown in FIG. 1 using the paste solder 10 (11) as described above,
The surface mount component 1 is mounted on the printed circuit board 5 through the following steps.
will be fixed.

First, when the glue is passed through a flow furnace in a high temperature atmosphere, the low melting point solder grains 10a melt as shown in FIG. 10b is also melted, and the paste solder is completely melted.

This melting step can be achieved by simply transporting the paste solder 10 through a reflow oven.

This does not mean that the temperature inside the reflow oven is uniform everywhere, and the temperature is highest in the center. Therefore, when using solder grains at 183°C as the high melting point solder grains 10b, the temperature is controlled so that the temperature at the center of the reflow oven is 183°C or higher, and the temperature at the periphery of the reflow oven is usually lower than this temperature. .

As a result, a temperature difference occurs along the conveyance path of the printed circuit board 5, and this temperature distribution causes the low melting point solder grains 10a to
is melted first, and then the high melting point solder grains 10b are melted.

Of course, this temperature difference may be actively created to melt the low melting point solder grains 10a in the preheating step, and melt the high melting point solder grains 10b in the next main heating step.

FIG. 3 is a diagrammatic representation of the above-mentioned melting process. I will explain step by step.

First, a predetermined conductive layer 6. is formed on the printed circuit board 5.
A predetermined amount of the above-mentioned paste solder 10.11 is applied onto the solder 7, and the surface mount component 1 placed on the top surface thereof is temporarily fixed with the paste solder 10.11 (FIG. A).

In this state, it is transported into a reflow oven. Then, since the printed circuit board 5 passes through a low temperature region in the reflow oven, the low melting point solder grains 10a and 11a begin to melt.

In this case, if there is a temperature difference between the electrodes of the surface-mounted component 1, the higher temperature side will melt. FIG. 3B shows a state in which the low melting point solder grains 10a are melted. Therefore, the electrode 3 side can be easily joined by the melted low melting point solder particles 10a, and this melting causes a slight surface tension to act on the electrode 3 side, and the surface of the paste solder 10 is slightly lifted as shown in the figure.

On the other hand, the low melting point solder grains 11a on the electrode 4 side have not yet melted.

However, as described above, since the surface tension caused by the melting of the low melting point solder grains 10a is extremely small, this force is not enough to lift one side of the surface mount component 1. Therefore,
The Manhattan phenomenon does not occur.

When the printed circuit board 5 is roughly transported to the inside of the reflow oven, the internal temperature also rises, which causes the other low melting point solder grains 11a to also become molten, and the picture electrode 3
．． 4 are lightly joined (C in the same figure).

When the printed circuit board 5 is transported to the center of the reflow oven, the ambient temperature has risen to 190° C. or higher. Therefore, the high melting point solder particles 1ob also become molten, and the electrode 3 is completely fixed by the paste solder 10 (FIG. D). At this time, if there is a temperature difference between the electrodes 3 and 4, the high melting point solder grains 11b on the electrode 4 side are not in a molten state for the same reason as described above.

However, since the electrode 4 is bonded to the conductive layer 7 by the low melting point solder grains 11b, the Manhattan phenomenon does not occur in this case either.

When the electrode 4 is transported to the center of the reflow oven, the temperature on the electrode 4 side also becomes quite high.
The solder paste 11 is also melted, and the electrode 4 is also completely fixed by the paste solder 11 (see E in the same figure).

By using the paste solder 10 (11) in which low melting point solder grains and high melting point solder grains are mixed in this way, the incidence of Manhattan phenomenon can be almost completely eliminated.

Incidentally, when conventional paste solder is used for reflow processing in a vapor phase solder tank, the 1608 type (1.6 mm x 0
Out of 360 small ceramic capacitor chips (commonly referred to in the electronic parts industry as 8m-XO, 8mm), 16 chips suffered from Manhattan phenomenon and failed to be soldered. Therefore, the probability of occurrence of the Manhattan phenomenon is 4.4%.

On the other hand, when the paste solder according to the present invention was used, all 360 chips could be completely soldered. In other words, by using the paste solder according to the present invention, the probability of occurrence of the Manhattan phenomenon was reduced to 0%.

[Effects of the Invention] As explained above, in the present invention, since the paste-like solder is composed of at least two types of solder particles having different melting points, the melting temperatures are different.

Therefore, the surface tension generated by melting only the low melting point solder grains becomes small, and when applied to the mounting board of surface mount components as mentioned above, by using this paste solder, the Manhattan phenomenon of surface mount components can be reduced. It has practical benefits that can definitely wipe out.

Therefore, the paste-like solder according to the present invention is extremely suitable for use in a board device on which microscopic surface-mounted components formed into chips are mounted as described above.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part showing an example of a board device in which a surface-mounted electronic component is fixed using the paste solder according to the present invention, and FIG. 2 is a paste solder according to the present invention and its melting process. FIG. 3 is a diagram showing the fixing process of paste solder, FIG. 4 is a diagram showing the state of mounting on a printed circuit board, FIG. 5 is a diagram showing the occurrence of Manhattan phenomenon due to paste solder, and FIG. The figure shows another conventional mounting state, FIG. 7 is a plan view at that time, and FIG. 8 is an explanatory diagram of the self-alignment effect. 1...Surface mount component 3.4...Electrode portion 10.11...Paste solder 10a, 'lla...Low melting point solder grains 10b, llb
... High melting point solder grain patent applicant Iwa Co., Ltd. 1≧(I+): Hantu Regulations (lυ゛ha>r Figure 2 Figure 3 Figure 6 Procedural Amendment 1988 Patent Application No. 97947 3) , Relationship with the case of the person making the amendment Patent applicant 4, agent (1) The scope of claims in the specification is amended as shown in the attached sheet. (2) Same, page 2, line 12 "Eutectic solder" Next, add "grain J." Solder 8 from the other side.'' (4) Same, page 6, lines 10-11 ``At least...
"Nakireta" was corrected to "At least two types of solder grains with different melting points and a predetermined amount of liquid flux, etc. are mixed to form a paste, and the difference in melting points causes a time lag in the melting of the solder grains." (5) In the same page, line 14, before the words ``Low melting point solder grains,'' add a new line and add the following. "In the reflow process, when the paste solder of the present invention is put into a reflow oven together with a printed circuit board, the behavior of the solder is as follows." (6) Same page, line 16 of "Solder grains 10a" followed by (
lla)”. (7) Same, page 7, line 2 “Solder grain 10a (11a)”
is corrected to "solder grain 10a". (8) Same, page 9, line 13, "mixed" is corrected to "mixed completely, and liquid flux 10c is added to it." (9) Same page, line 15, add ``solder powder'' after ``the''. (10) Same, same page, line 17, ``It's about the same.'' is corrected to ``It's about the extent (I-shaped flux should be used in an appropriate amount).'' (11) Same, page 13, line 1, "Around the center" is corrected to "Around the center." (12) Same page, line 7 “j on the electrode 4 side”
"On the side," he corrected. (13) Same page, line 9, "solder grain 11b" is corrected to "solder grain 11a". (14) Same, page 14, line 6, take the line break after ``de'' and continue with ``nsa tip'' on the next line. (15) Same, 3 lines from the bottom of No. 15 “Printed circuit board”
should be corrected to "conventional printed circuit board". (16) Same, 2 lines from the bottom of the same page “Paste solder”
is corrected to "conventional paste solder". (17) Add the following on a new line after "High melting point solder grains" on page 16, line 7. '10c...Liquid flux' (16) In the drawings, Figures 1 and 2 are corrected as shown in the attached sheet. Claims (1) At least t) two types of solder grains having different melting points;
A paste-like solder, characterized in that a predetermined amount of liquid flux or the like is mixed to form a paste, and the solder particles are melted with a time difference due to the difference in melting point.

Claims (1)

[Claims] (1) A paste-like solder made by mixing predetermined amounts of at least two types of solder grains with different melting points to form a paste.