JP3444096B2 - Lead-free method and solder mounting method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Pb-free solder-mounted product substrate, an LSI, a terminal of a component, and the like, and a simple recovery method of the Pb-based solder.

[0002]

2. Description of the Related Art Pb has a low cost and a high utility value, and has been actively used for soldering and the like. Also,
The problem of environmental pollution of Pb has not been pointed out.

[0003]

Recently, the problem of environmental pollution of Pb has been highlighted. It is a fact that printed circuit boards of electrical products that have already been left unattended are exposed to rainwater and dissolved in groundwater.

Based on these facts, there is an increasing need to easily remove Pb from a conventional mounted product including a substrate, an LSI, a component, etc., which is connected with a solder containing Pb.

An object of the present invention is to easily make Pb-free a product which is already made of a solder containing Pb. Further, the purpose is to make the mounting portion free of Pb and recover the Pb.

[0006]

Therefore, for example, in the mounting products in which Sn-Pb solder or Sn-Pb-Bi solder is used for substrate terminals, LSI terminals, component terminals, etc. Paying attention to the fact that an alloy layer of a Ni metallized layer and Sn is formed and Pb does not enter, replacing the solder composition containing Pb on this alloy layer with a Pb-free composition and recovering the Pb. did.

A cross-sectional model immediately after soldering with Sn—Pb solder on a Cu pad is shown in FIG. 1 (a), and a cross-sectional view after further aging immediately after soldering or when an alloy layer after use in an actual machine is formed The model is shown in Fig. 1 (b). In reality, a thin Cu—Sn alloy layer of 0.1 μm level is formed immediately after soldering. The alloy layer is usually made of Cu6Sn5 with a thickness of several μm. In addition, Cu3Sn may be formed on the Cu side when the thermal history is repeated due to the thermal effect such as aging or due to repair or the like. In both cases, Pb does not enter the alloy layer. In addition,
In the case of Ni, usually only an alloy layer of Ni3Sn4 is formed.

That is, in order to achieve the above-mentioned object, the present invention provides a substrate on which electronic components are mounted with Pb-containing solder.
It is dipped in b-free solder, Pb contained in the Pb-containing solder is diffused into the Pb-free solder by its concentration gradient to replace the solder composition, and the Pb is recovered in a solder bath.

If the amount of Pb-free solder is sufficient with respect to the amount of Pb-containing solder on which electronic components are mounted, P
Since b diffuses into the Pb-free solder due to its concentration gradient, the mounting portion of the electronic component and the substrate can be made Pb-free.

When the Pb-containing solder is Sn-Pb-based solder or Sn-Pb-Bi-based solder, the composition of the Pb-free solder to be replaced is Sn-Bi-based solder, Sn-Bi-Ag-based solder, Sn-Bi-Zn-based solder, Sn-based solder, Sn-Ag-based solder, or In, Cu, Ga, Ni, Sb, Pd, and P of which are 1
It is desirable that the solder be one kind or a small amount of two or more kinds added.

In this way, if the main components of the Pb-containing solder and the Pb-free solder are made common, the diffusion due to the concentration gradient of Pb is further activated, and the P of the mounting portion is
Replacement with b-free solder becomes easy.

By changing the Pb-free solder to Sn-Bi solder, Sn-Bi-Ag solder, or Sn-Bi-Zn solder, the solder substitutability at a low temperature, the substrate,
It can be expected to reduce thermal effects on LSIs and parts, wettability, compatibility with metallization, long-term storability against recycling, fisker resistance, and wettability. It should be noted that B
Even if i is mixed, since the alloy layer with Sn has already been formed in the Cu and Ni metallized layers of the printed circuit board, it is expected that the problem of initial strength reduction will not occur.

Since the amount of the preliminary solder is smaller than the amount of the solder supplied by the paste or the like by about one digit, the melting point does not matter depending on the composition.

That is, the thickness of the solder usually attached on the Cu pad is 20 to 30 μm at the center of the pad. On the other hand, the supply thickness of the solder paste for connecting LSIs, parts, etc. is about 100 to 200 μm, which is about one digit larger.

On the other hand, in order to immerse the substrate in Pb-free solder, a conventional flow solder or wave solder may be used. That is, Pb using the above-mentioned concentration gradient
If it is a free method, a conventional process can be used. For example, in a Pb-free method using a wave solder, the flow rate of the Pb-free solder is controlled to
b can be diffused into the solder bath of the wave solder.

When strict solder composition management is required, the substrate and the electronic component may be made Pb-free a plurality of times via the flow solder or the wave solder provided in multiple stages.

That is, when using a wave solder or the like, the Pb-free solder of the solder bath has a composition that gradually contains Pb depending on the number of times of use. Therefore, in order to efficiently make the mounting portion Pb-free, a wave solder or the like is provided in multiple stages. For example, the LSI and components are removed in the first stage, the Pb is roughly diffused, and the board removed in the second stage. It suffices that the mounting parts such as LSI, parts, etc. be Pb-free.

In order to recover Pb diffused in the solder bath of the wave solder, the following may be carried out.

Since Pb has a higher specific gravity than others, it precipitates on the bottom of the solder bath after a long time. Therefore, a precipitation tank with a small flow is provided at the bottom of the solder bath of the flow solder or the wave solder, and a temperature gradient is provided in the precipitation tank from the upper part to the lower part so that the upper part has a high temperature. By providing a temperature gradient from the upper part to the lower part in the precipitation tank in this way, the upper part is solidified and the low melting point multi-component solder containing a large amount of Pb with a large specific gravity can be precipitated in a liquid state and recovered. The bath surface can always be brought close to the state of low Pb.

Up to now, it has been described that the Pb is made free, but if Pb of the mounting portion is diffused, the mounting portion can be remounted by Pb-free solder as a result.

In addition, the substrate and the electronic component can be removed by this, and each can be reused.
Needless to say, even in this case, the substrate and the electronic component are Pb-free. In particular, the removed board can be metalized and reused with high reliability by replacing the solder composition.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a cross section of an embodiment of a wave soldering device. In this example, Sn-37Pb eutectic solder was used as the Pb-containing solder, and Sn-58Bi eutectic solder was used as the Pb-free solder.

The operation of this wave soldering device is as follows.

For example, the LSI 1, the component 2, etc. are Sn-37.
Printed circuit board 4 surface-mounted with Pb eutectic solder 3
Is fixed upside down on the carrier 5 and moved to the right. S
The motor flow of the n-58Bi eutectic solder (melting point: 138 ° C.) 9 bath is counterclockwise by the motor 7. The flow of Sn-58Bi eutectic solder by the motor 7 is formed so as to immerse the substrate mounted on the carrier 5 from the ejection port of the solder flow path.

In this wave soldering device,
The temperature is set to 210 to 220 ° C., which is a level that does not affect the heat of the substrate. Further, in this embodiment, as in the case of normal soldering, a flux, for example, a rosin-based flux containing 0.2% of chlorine is applied. This is Sn-58B
i-eutectic solder (melting point 138 ° C) has wettability of Sn-37P
This is because the surface oxide film is stronger because it is worse than the eutectic solder (melting point 183 ° C.) and is Sn-based.

The molten Sn-58Bi eutectic solder is
When the substrate mounted on the carrier 5 is immersed, the Sn-37Pb eutectic solder on the mounting portion of the substrate shifts from its melting point to a molten state. When the Sn-58Bi eutectic solder and the Sn-37Pb eutectic solder are in a molten state, Pb diffusion gradually starts. As can be seen from the figure, the amount of Sn-37Pb eutectic solder 3 used for connecting the substrates is sufficiently smaller than the amount of Sn-58Bi eutectic solder 9, so that Pb is 0% to 37%. Easily spread towards%.

The Pb diffused in the solder bath gradually deposits in the lower part of the solder bath due to its specific gravity. Since the solder that sinks downward is exposed to high temperatures for a long time, it has a high specific gravity.
b and Bi increase. Sn-Bi with high Pb concentration
-Pb solder is recovered from the recovery port 10, and precious metal element,
Pb is recovered by sending it to the separation and recovery of Bi, Sn and the like. P
The method of collecting b will be described later.

Similarly, since Bi also diffuses into the mounting portion of the substrate, it becomes a Sn-Bi terminal, and as a result, the solder composition in the mounting portion of the electronic component and the substrate is replaced with the Pb-free solder composition and re-mounted. can do.

The present invention aims at recovering the solder containing Pb used for the substrate, and the Pb recovered substrate,
Of the LSIs, parts, etc., useful ones are used for remounting, and it is not always necessary to remount.

Next, an example will be described in which the substrate and the electronic components are made Pb-free and the respective components are removed. Also in this case, since Pb-free is made by concentration diffusion in the removal process, both the substrate and the component are removed in the Pb-free state.

A structure for removing parts and the like will be described below. Other configurations are the same as those of the above-mentioned wave soldering device.

In the above-mentioned wave soldering device, 21
The temperature was set to 0-220 ℃, but this temperature was Sn-58.
The removal temperature is sufficient for Bi eutectic solder. There are some parts that are difficult to remove just by flushing them. Unlike soldering, it is desirable that the removal flow be a turbulent flow with disturbed wave height. Further, it is effective to intentionally vibrate the substrate, and it is effective to attach a small vibration exciter capable of 10 to 500 Hz level to the carrier or devise to give an impact from the outside. It is effective for the replacement to lift up the carrier or the substrate for a moment and apply an impact from the outside to remove the LSI, components, etc. or to scatter the solder. Further, by spraying high temperature N2 gas, the solder in the through holes can be easily blown off. Through-hole joints must be forcibly mechanically melted and withdrawn, and then replaced by blowing N2 gas.

The LSI, components, etc., which have melted the solder and are separated from the substrate, gather around the suction port 8 of the apparatus, but are not sucked into the solder because they are lighter than the solder.

In the case of a straight lead which is relatively easy to remove with a through hole joint, the LSI and components can be removed by forcibly applying an impact in the molten state. However, since the solder in the through hole is not yet removed, it is possible to scatter and remove it by blowing a high temperature inert gas such as N2. Just in case, Sn-
It is necessary to replace it with Bi and blow it off with N2 gas.
Solder has a very low viscosity when it is in a liquid state.
-37Pb eutectic has a melting point value of 2.92 mPa · s and specific gravity [Bi: 10 g / cm3, Pb: 10.7 g / cm3.
3, Sn: 7 g / cm3] is high, so it can be easily dropped with some impact.

It is also possible to use a method in which halogen does not enter in an N2 atmosphere having an O2 purity of about 100 to 1000 ppm.

For a paper phenolic substrate or the like having poor heat resistance, Sn-58Bi eutectic solder having a low melting point is used, and a strong flux is used in the atmosphere to reduce the heat influence on the substrate. The same is possible with a wave soldering device at ° C.

A small amount of solder remains on the Cu pad of the substrate from which components and the like have been removed by wave soldering or the like.
It is only about 1/10 of the amount of newly supplied solder. Therefore, a large Bi content at this point does not cause any particular problem in terms of reliability.

Next, an example will be described in which the above-mentioned substrate from which the LSI, components and the like have been removed is replaced with a highly reliable metallization having a higher melting point.

In order to reuse the substrate from which the LSI, parts, etc. have been removed and replace it with a highly reliable metallization having a high melting point, Sn-15Bi (melting point: liquidus line; 212 ° C., solidus line;
(160 ° C.) A second wave soldering with solder was performed at 235 ° C. This composition has good wettability and is suitable for soldering after metallization. Since the substrate has a melting point of 150 ° C. or higher even when it is stored for a long period of time, it is a metallization that can withstand long-term storage. Originally, in order to improve the reliability of metallization, it is desired to replace with a composition having a lower Bi concentration, but since the wave soldering temperature becomes high and the thermal deterioration of the substrate becomes a problem, a composition with a lower Bi concentration is selected. The substitution raises the melting point and is therefore difficult with this feeding method.

However, a heat-resistant glass polyimide substrate,
There is no problem with BT substrates, ceramic substrates, etc. For example, in the case of a glass polyimide substrate, Sn-5Bi (melting point: liquidus line; 228 ° C., solidus line; 200 ° C.) solder can be used. In this case, the wave soldering temperature may be set to 260 ° C.

By substituting the solder composition whose melting point is adjusted according to the heat-resistant temperature of the substrate as described above, more reliable metallization is possible and the substrate can be easily reused.

Next, a method of recovering Pb diffused in the solder bath will be described.

Assuming that the above-mentioned Sn-58Bi eutectic solder wave soldering tank (1000 kgf) is used, and assuming that 50 gf of Pb is put into the wave soldering tank by one replacement per substrate, 20000 sheets are replaced. Then, the simple calculation is 100 kgf, and the Pb concentration is 10%. The composition of the averaged solder bath was calculated to be (42%
Sn-58% Bi) x 0.90 and the remaining 10% Pb, the composition of which is (38% Sn-58% Bi-10Pb).
Becomes When displayed in the ternary phase diagram of Sn-Bi-Pb shown in FIG. 3, the composition has 14 points. The more you do,
Since the Pb concentration of the solder bath increases, it is necessary to use it up to an allowable concentration, or use a bath having two or three stages of higher purity. If a concentration gradient is applied in the solder bath, recovery efficiency will be improved.

An example of the solder recovery method is shown below.

Referring to FIG. 3, Sn-58% Bi (E
3:15) has a melting point of 138 ° C., but the Pb concentration decreases to about 32% due to the inclusion of Pb.
(Et: ternary eutectic 16) has a minimum melting point of 100 ° C
become. Therefore, a temperature gradient between 138 ° C. and 100 ° C. is created, and for example, a specific location of the tank is provided, the upper layer is heated to a high temperature, and the lower layer is cooled to force a Pb-rich composition with a low melting point in the lower layer. Can be formed as desired.
At this time, it is also possible to accelerate liquefaction by giving impact, vibration or the like. Since the liquefied portion is a Pb-rich layer, it can be taken out in a liquid state.

That is, when Pb does not enter as it is cooled, it solidifies at 138 ° C. The solidification temperature becomes 138 ° C. or lower due to the inclusion of Pb. By making the upper side of the device high temperature and the lower side low temperature, when the Pb concentration rises, the liquid can be made to drip from the gap between the solidified and contracted solids.

Further, as shown in FIG. 4, a centrifuge mechanism 17 (rotating shaft: 21) is provided in the solder bath 9 or a bath guided from the solder bath, and Pb-Bi rich solder 18 having a high specific gravity is replaced with Sn rich. Separated from the solder 19 of
Recycle the rich composition again. The recovered Pb-Bi rich solder 20 is attached to the electronic parts such as Au, Pd, I.
Noble metals such as n and Ag are taken out, Pb and Bi are dissolved in water and dilute sulfuric acid, and PbS and the like are separated to separate Bi. Further, Sn can be electrolyzed by making it a strong alkali.

Finally, application to Sn-Ag-Bi type Pb-free solder was examined. As an example, Sn-3Ag-1
0 Bi solder (melting point: liquidus line; 208 ° C., solidus line; 17
1 ° C) was used. The printed circuit board from which the LSI and the components were removed was passed through a wave soldering bath of max 235 ° C. and replaced with a Sn-3Ag-10Bi solder composition. FIG. 5A shows a state in which the Pb-63Sn eutectic solder 12 is pre-soldered and formed on the Cu pad 11 of the printed circuit board 4 having no LSI or components. This is Cu
An alloy layer of Cu6Sn513 is formed between the solder and the solder. Even if it is completely replaced with Sn-58Bi eutectic solder,
The Cu6Sn5 alloy layer remains almost unchanged. Further Sn-3A
When flowed in the g-10Bi solder bath, Sn-3Ag-10Bi solder is pre-soldered on the alloy layer Cu6Sn5. If the solder is strongly blown off during the replacement as shown in FIG. 5 (b), the alloy layer is exposed and the surface of the alloy layer is easily oxidized, so care must be taken when reusing.

[0050]

According to the present invention, Pb- which is already on the market
This makes it possible to efficiently recover Pb from the substrate, parts, etc. of the product connected by Sn solder. In addition, Pb-free metallization that enables reuse can be provided at a low cost by using an existing process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a joint portion joined by Sn—Pb immediately after soldering and after use in an actual machine.

FIG. 2 is a sectional view showing how to remove an LSI and components by wave soldering.

FIG. 3 shows a ternary system state of Sn-Pb-Bi solder.

FIG. 4 shows a cross-sectional view of a model in which a centrifugal separation mechanism is provided in a solder bath.

FIG. 5 is a cross-sectional view showing a replacement state on a pad of a printed circuit board.

[Explanation of symbols]

1: LSI 14: 38% Sn-5
8% Bi-10Pb 2: Component 15: Sn-58% B
i (E3) 3: Sn-37Pb eutectic solder 16: ternary eutectic 4: printed circuit board 17: centrifugal separation mechanism 5: carrier 18: Pb-Bi rich solder 7: motor 19: Sn rich solder 8: Suction port 20: Pb-Bi rich solder 9: Sn-58Bi eutectic solder 21: Rotating shaft 10: Recovery port 22: Sn 11: Cu pad 23: Pb 12: Sn-37Pb eutectic solder 24: Sn3Cu 13: Cu6Sn5

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiharu Ishida 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd. Inside the Institute of Industrial Science, Hitachi, Ltd. (56) Reference JP-A-9-51158 (JP, A) ( 58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 3/34 B23K 35/26

Claims (10)

(57) [Claims] 1. A substrate on which an electronic component is mounted by Pb-containing solder is dipped in Pb-free solder to melt the Pb-containing solder, and Pb contained in the Pb-containing solder is converted into a Pb-free solder by a concentration gradient. A Pb recovery method, which comprises recovering the Pb by diffusing it into a Pb-free solder. 2. The Pb recovery method according to claim 1, wherein the temperature of the Pb-free solder is higher than the melting point of the Pb-containing solder to recover the Pb. . 3. The Pb recovery method according to claim 1, wherein the Pb-containing solder is Sn—Pb based solder or Sn—Pb solder.
-Bi solder, and the Pb-free solder is Sn-
Bi-based solder, Sn-Bi-Ag-based solder, Sn-Bi
-Zn solder, Sn solder, Sn-Ag solder,
Or In, Cu, Ga, Ni, Sb, P
A method of recovering Pb, characterized in that it is a solder in which one or more kinds of d and P are added. 4. Pb according to any one of claims 1 to 3.
A method for recovering Pb, comprising recovering the Pb using a flow solder or a wave solder. 5. The Pb recovery method according to claim 4, wherein the Pb is recovered via the flow solder or the wave solder provided in multiple stages. 6. A substrate on which an electronic component is mounted by Pb-containing solder is immersed in Pb-free solder, and Pb contained in the Pb-containing solder is diffused into the Pb-free solder due to its concentration gradient, And a solder mounting method comprising remounting the electronic component. 7. The solder mounting method according to claim 6, wherein the Pb-containing solder is Sn-Pb-based solder or Sn-P.
b-Bi-based solder, and the Pb-free solder is Sn-Bi-based solder, Sn-B
i-Ag solder, Sn-Bi-Zn solder, Sn solder, Sn-Ag solder, or I
A solder mounting method characterized in that it is a solder in which one kind or two or more kinds of n, Cu, Ga, Ni, Sb, Pd, and P are added. 8. The solder mounting method according to claim 6, wherein the board and the electronic component are remounted using a flow solder or a wave solder. 9. The solder mounting method according to claim 8, wherein the board and the electronic component are passed a plurality of times through the flow solder or the wave solder provided in multiple stages, and re-mounted. Solder mounting method. 10. The method for recovering Pb according to claim 4 or 5, wherein the flow solder or the wave solder is provided with a settling tank at a lower bottom of the solder bath, and an upper part is heated from an upper part to a lower part of the precipitation bath. The Pb recovery method is characterized by recovering the Pb by providing a temperature gradient.