WO2008035758A1

WO2008035758A1 - Lead-free solder paste

Info

Publication number: WO2008035758A1
Application number: PCT/JP2007/068363
Authority: WO
Inventors: Kunihito Takaura; Kazuya Kitazawa
Original assignee: Senju Metal Industry Co., Ltd.
Priority date: 2006-09-22
Filing date: 2007-09-21
Publication date: 2008-03-27
Also published as: JPWO2008035758A1; JP4162707B2

Abstract

Conventional Sn-Zn lead-free solders have the drawback of joint strength dropped when placed in an environment of high humidity. Although alloys having been improved in strength by addition of a minute amount of Group 1B metal or Al to solder have been proposed, they have poor wetting property and thus have drawback and advantage. There is provided an Sn-Zn lead-free solder paste excelling in prevention of joint strength decrease and prevention of insulation resistance deterioration (for example, prevention of deterioration of the insulation resistance of soldered chip capacitor). The Sn-Zn lead-free solder paste is a solder paste of alloy powder blended with a flux, to which 10 to 30% of guanidine derivative is added. Accordingly, the pH value of flux residue after soldering is adjusted to neutrality or basicity to thereby suppress the generation of Zn+ ion. Further, hydroxyl of amine and Zn in the solder are reacted with each other so as to form a Zn-H2O passive state, thereby preventing a strength decrease of soldered part. Therefore, the joint strength can be maintained even in an environment of high humidity.

Description

Specification

Lead-free solder paste

Technical field

TECHNICAL FIELD [0001] The present invention relates to a solder paste used for soldering electronic equipment, and more particularly to a Sn—Zn-based lead-free solder paste.

Background art

As a method for soldering electronic components, there are a brazing method, a flow method, a reflow method, and the like.

[0003] The brazing method is a method of soldering by applying a greased solder wire to a soldered part! /, And heating and melting the solder wire with a soldering iron. This brazing method has a problem in productivity because soldering is performed for each soldered portion, and is not suitable for mass production.

[0004] The flow method is to perform soldering by bringing the soldering surface of the printed circuit board into contact with the molten solder, and is capable of soldering the entire printed circuit board in one operation. It is. However, this flow method can form a bridge where solder adheres across electronic components with a narrow pitch, or molten solder directly onto electronic components that are vulnerable to heat. In some cases, the electronic components may be damaged due to heat, resulting in functional deterioration. In addition, when a connection component such as a connector is mounted on the soldering surface of the printed circuit board, there is a problem that the molten solder penetrates into the connector hole and cannot be used.

[0005] In the reflow method, a solder paste consisting of solder powder and flux is applied only to the necessary parts of the printed circuit board by a printing method or a discharge method, and an electronic component is mounted on the applied part, followed by heating like a reflow furnace. This is a method in which solder paste is melted by an apparatus and the electronic component and the printed circuit board are soldered. This reflow method not only enables soldering at many locations in a single operation, but also reduces the occurrence of bridging even for electronic components with narrow pitch, and also improves productivity and reliability that solder does not adhere to unnecessary locations. Excellent soldering is possible.

[0006] By the way, the solder paste used in the conventional reflow method has solder powder of Pb-Sn compound. It was money. This Pb-Sn alloy has an eutectic composition (Pb_63Sn) with a melting point of 183 ° C, and it has little heat effect even on electronic components that are vulnerable to heat or has excellent solderability. There are few occurrences of soldering defects such as dewetting! When an electronic device soldered with a solder paste using this Pb-Sn alloy becomes old or fails, it has been disposed of without being upgraded or repaired. When discarding printed circuit boards, the power of landfill disposal instead of incineration landfill disposal is because the solder is metallicly attached to the copper foil of the printed circuit board, and the copper foil and solder are separated. This is because it cannot be reused. When acid rain comes into contact with this landfilled printed circuit board, Pb in the solder elutes and contaminates groundwater. There is a concern that Pb poisoning will occur if people and livestock drink Pb-containing groundwater for many years. Therefore, the so-called “lead-free solder” that does not contain Pb has been strongly demanded by the electronic equipment industry.

[0007] Lead-free solder is composed mainly of Sn, and currently used lead-free solder is Sn-3.5Ag (melting point: 221 ° C), Sn_0.7Cu (melting point: 227 ° C), Sn_9Zn (melting point: 199 ° C), Sn-58 Bi (melting point: 139 ° C) and other binary alloys, Ag, Cu, Zn, Al, Bi, In, Sb, Ni, etc. A third element such as Cr, Co, Fe, Mn, P, Ge, or Ga is appropriately added. The “system” in the present invention is an alloy itself or an alloy to which one or more third elements are added based on a binary alloy. For example, the Sn-Zn alloy is an Sn-Zn alloy itself or an alloy obtained by adding one or more of the aforementioned third elements to Sn-Ζη, and the Sn-Ag alloy is an Sn-Ag alloy itself or Sn_Ag as described above. An alloy with one or more elements added.

[0008] Sn-Ag-based lead-free solder, Sn-Cu-based lead-free solder, etc. have a melting point of 220 ° C or higher. Therefore, when solder paste is used in the reflow method, the peak temperature force during reflow is ¾50 ° C. As a result, there is a problem that electronic components and printed circuit boards are thermally damaged.

[0009] Sn-Bi eutectic lead-free solder has a melting point of around 139 ° C, and even when used as a solder paste in the reflow method, the peak temperature is 200 ° C or less. There is no thermal effect on the printed circuit board. However, the lead-free solder containing a large amount of Bi has a problem in heat resistance because its melting point is too low. In other words, the case inside the electronic device When the heat generated by the power transistor etc. is high, the soldered portion of the printed circuit board soldered with the lead-free solder may be peeled off due to a decrease in bonding strength. In addition, Pb-free solder containing a large amount of brittle Bi has a problem that it can be easily peeled off even if a slight impact is applied to the soldered part.

[0010] The lead-free solder of Sn-9Zn eutectic has a melting point of 199 ° C, which is close to the melting point of conventional Pb_Sn eutectic solder. The power is less than ¾30 ° C and there is little thermal effect on electronic components and printed circuit boards. However, Sn_9Zn eutectic solder paste has poor solderability to the soldered part of copper and does not adhere to solder! /! “Unsoldered” or wet! / In some cases, soldering defects such as “dewetting” that would cause repellency! Such poor soldering deteriorates the strength and strength of the joint when the joint strength is weakened. In addition, the solder paste of Sn_9Zn eutectic has been discolored from the interface of the copper foil and copper land after many years have passed since the solder paste of the copper land printed circuit board and the copper lead has been soldered. There was something to do. The peeling of the soldered portion causes a failure in the electronic device. Furthermore, the Sn_9Zn eutectic solder paste also had a chip standing that caused a small chip component to rise during soldering. When a chip stands on a printed circuit board, the electronic device incorporating it cannot function at all.

[0011] Accordingly, various Sn-Zn-based lead-free solders added with a third element have been proposed to improve the problems in Sn_9Zn eutectic solder paste. For example, the solder paste that has improved solderability includes Sn-8Zn_3Bi lead-free solder paste in which Bi is added to an alloy near Sn-Zn eutectic, and this solder paste is currently widely used. . In addition, the present applicants have proposed lead-free solder in which Ag is added to an alloy near Sn_9Zn eutectic to improve corrosion resistance.

[0012] Sn-Zn-based lead-free solder has a melting point close to that of conventional Sn_Pb solder and uses Zn, which is an essential component for humans. Therefore, it is more harmful to the human body than other lead-free solders. Not that, Zn has excellent properties compared to other lead-free solders, such as In, Ag, Bi, etc. For this reason, Sn-Ag lead-free solder is used as solder paste solder, despite its poor solderability. One solder does not have heat resistance of the part! /, So it cannot be used! /

Yes

[0013] However, Sn-Zn-based lead-free solder, when soldered on a commonly used Cu land printed circuit board such as FR-4, and then left at high temperature, the soldering joint strength decreases. There was a problem. This is because the reactivity between Zn and Cu is high. When a Cu land substrate is used, Zn in the Sn-Zn lead-free solder passes through the alloy layer and remains in the Cu layer if the high temperature state is continued for a long time. It penetrates and generates a lot of voids between the intermetallic compound called Kirkendall void and solder (see Non-Patent Document 1). In other words, the generation of voids decreases the bonding strength of soldering and deteriorates reliability. For this reason, when using Sn-Zn lead-free solder, it is necessary to create an M barrier by applying M plating to Cu land. However, since Ni is poor in wettability, Au plating is applied to Ni. It cannot be used without it. Therefore, when using Sn-Zn based lead-free solder, Au plating is essential, which raises the problem of increased manufacturing costs for electronic devices.

In addition, when Sn—Zn-based lead-free solder is soldered to a Cu land printed circuit board, humidity is a factor that decreases the joint strength along with the temperature. When the humidity is high, Zn elutes from the alloy phase to form an oxide, and cracks occur at the interface between the oxide and the solder. This phenomenon is prominent even at temperatures below S100 ° C when the humidity exceeds 80%.

[0015] As a method to improve the soldering strength of Sn-Zn-based lead-free solder and Cu at high temperatures, a method of adding a Group 1B metal to Sn-Zn-based lead-free solder powder is proposed. (Patent Document 1). However, since the 1B group metal powder added to the Sn-Zn lead-free solder powder is more than 10% of the Sn-Zn lead-free solder powder, do not raise the peak temperature of reflow! / This eliminates the advantage of Sn-Zn lead-free solder that the solder does not melt and can be reflowed with almost the same temperature profile as conventional Sn-Pb solder.

[0016] In addition, there has been proposed a method for improving the soldering strength with Cu at high temperature by adding a small amount of A1 to Sn-Zn lead-free solder (Patent Document 2). However, since A1 is a metal that easily oxidizes, it is oxidized prior to other components during the production of solder powder, and the components of 0.002% to 0.008% by mass disclosed in this document must be maintained in mass production. Is Have difficulty. In addition, a small amount of A1 added to Sn-Zn lead-free solder is effective for improving the soldering strength at high temperatures. It has no effect on moisture resistance. High temperatures such as 85 ° C and 85% RH, high It cannot withstand humidity.

[0017] The present applicant, Sn-Zn based lead-free solder and Cu under high temperature (→ high temperature and high humidity, not related to high temperature such as 150 ° C. There is no definition of high temperature and high humidity Solder paste flux as a method to improve soldering strength at 60 ° C / 90% RH and 85 ° C / 45% -85% RH (especially at 85 ° C / 85% RH) A Sn-Zn lead-free solder solder paste (Patent Document 3) in which fluid paraffin or paraffin wax is added is disclosed.

In addition, Sn-Zn lead-free solder powder (Patent Document 4) that adsorbs amine on the surface of Sn-Zn lead-free solder powder and prevents oxidation of the solder powder due to preheating during reflow is disclosed.

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-224880

Patent Document 2: US Pat. No. 6,361,626

Patent Document 3: Japanese Patent Laid-Open No. 2005-21958

Patent Document 4: Japanese Patent Laid-Open No. 2001-212692

Disclosure of the invention

Problems to be solved by the invention

[0019] By the way, as described above, there is a problem that when the Sn-Zn alloy and Cu are bonded and exposed to high temperature and high humidity, the bonding strength of the solder is remarkably lowered. For this reason, a commonly used Cu land substrate such as FR-4 cannot be used, and an expensive Au-plated printed circuit board is indispensable, resulting in increased manufacturing costs! In addition, there is a method of maintaining a high temperature strength by adding a small amount of additive element to the Sn-Zn alloy for bonding with Cu, but there is a problem that a small amount of additive element deteriorates the wettability in the Sn-Zn alloy. there were. Sn-Zn lead-free solder solder paste with liquid paraffin and paraffin wax added to the flux of solder paste has an excellent effect on strength at high temperatures S, flow added to the flux Paraffin or paraffin wax remains almost in the flux residue after soldering, and if a large amount of liquid paraffin or paraffin wax is added in order to expect a moisture-proof effect, There was a problem that the paste residue increased and the appearance was uncomfortable. In addition, when soldering with Sn-Zn lead-free solder paste, the ceramic capacitor soldered when placed under high temperature and high humidity causes the insulation resistance to deteriorate.

Means for solving the problem

[0020] In the Sn-Zn-based lead-free solder paste, the present inventors have found that the soldered portion is damaged in a high-temperature and high-humidity environment. Degradation causal force of capacitor insulation resistance S, due to corrosion of Zn, and by making the flux residue after soldering neutral and basic, the Zn-H20 series in the measured corrosion area diagram of Zn The present inventors have found that it is possible to control to the passivated region and completed the present invention.

[0021] The reason why the strength of the soldered portion of Cu soldered with Sn-Zn lead-free solder is reduced is that an easily oxidized Cu-Zn alloy layer is formed at the interface between copper and solder. . Conventional Sn-Pb solder, Sn-Ag lead-free solder and Sn-Bi lead-free solder, etc., when soldered with Cu, Sn and Cu in the solder react with the Sn-Cu alloy layer Form. When Cu is soldered with Sn-Zn lead-free solder, a Cu-Zn alloy layer is formed. When the Cu-Zn alloy phase is placed in a high-temperature and high-humidity environment, Zn elutes from the alloy phase and Zn oxide is produced. For this reason, a crack is generated at the interface between the Zn oxide and the solder, and finally, it peels off at the joint interface. Similarly, the strength of the solder itself deteriorates due to the formation of Zn oxide.

[0022] The phenomenon of reducing the bonding strength occurs not only in the Sn_9Zn binary alloy but also in the Sn-3Bi_8Zn composition, which is often used as the composition of Sn-Zn-based lead-free paste. Conventionally, as described in Patent Documents 1 and 2, a method of preventing a decrease in strength by adding a small amount of Group 1B metal or aluminum to Sn-Zn lead-free solder has been used. These methods assume high temperatures in an environment with an average humidity of 40-60%. The soldered part is hardly exposed to high temperatures of 100 ° C or more except in-vehicle parts and power supply parts. In Japan, there are many environments with high humidity where the humidity is over 80%.

[0023] As described above, the cause of the decrease in strength of Sn-Zn lead-free solder is the ionization of Zn. The Therefore, in the present invention, a passive film is formed on Zn by adding a material that adjusts the pH of the flux residue after soldering to neutral and basic so that Zn + ions are not generated. By suppressing the elution of Zn, the strength of the soldered part is prevented from decreasing. By adjusting the pH of the flux residue to the pH that is the passivating region of the Zn-H20 system, the strength of the soldering part is prevented from decreasing by forming a passivating film of Zn (OH) 2. Yes. The passivity of Zn-H20 system is not formed unless the flux residual force is in the neutral or basic region. In the present invention, the formation of Zn—H20 passivity in the flux residue is effective for the deterioration of the insulation of the chip capacitor as well as the reduction in the strength of the Sn—Zn lead free solder. In order to prevent the strength of Sn-Zn lead-free solder from lowering the strength, it is important to bias the pH of the flux residue to basic S. If the flux of the solder paste itself is biased to basic, Solder balls are generated and soldering defects are likely to occur. In other words, in order to obtain good soldering with fewer solder balls, the solder paste flux should be biased toward the acidic range. In the present invention, a guanidine derivative has been found as a material for adjusting the pH of the flux residue after soldering in order to solve this conflicting problem.

[0024] Guanidine is an amine having a structure of (NH2) C = NH, and a guanidine derivative substituted with H of its amino group is used as a vulcanization accelerator for organic rubber. The guanidine derivative has a high heat resistance, with H of the amino group substituted by an aromatic hydrocarbon, a melting point of around 150 ° C. This guanidine derivative has the property that it remains reliably in the flux residue because it is hard to be decomposed by heat, which is strongly basic as an amine. Guanidine derivatives have the same solderability as organic acids. For this reason, the flux residue after soldering can be adjusted to a pH value of 7 to 11, and solderability is also good.

[0025] The present invention uses 1,3 diphenyldanidine, 1,3 di-0-tolylguanidine, and 1-0-tolylbiguanide, more preferably the same effect as long as it is a guanidine derivative. And good. These guanidine derivatives may be used alone or in combination of two or more. These guanidine derivatives are also excellent in solderability with solder paste that only adjusts the pH of the flux residue. In general, the addition of amines in the flux biases the flux to be basic, thus hindering the action of the activator. Only However, the guanidine derivatives of the present invention do not inhibit the action of the active agent.

[0026] The present invention is a solder paste in which a Sn-Zn-based lead-free solder alloy powder and a flux are kneaded, wherein a guanidine derivative is added to the flux.

The Sn—Zn alloy powder in the present invention includes Sn—Zn binary alloy powder and ternary or higher alloy powder obtained by adding other elements to the binary alloy powder.

The invention's effect

[0027] By using the solder paste of the present invention, it is possible to prevent a decrease in bonding strength that occurs in a Sn-Zn-based lead-free solder alloy even in an environment of high temperature and high humidity, and a general lead-free solder alloy The Sn-Ag-Cu solder alloy used as a high temperature can not be used at a high temperature! /, And the heat resistance is low, and electronic parts can be used with high reliability.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] The guanidine derivative used in the present invention adjusts the pH of the flux unlike Patent Document 4 and the like, so it is always used together with the flux. The amount of amine used to coat the solder powder of Patent Document 4 is not sufficient to adjust the pH of the flux residue, and it is not possible to use it by coating the powder!

If the amount of the guanidine derivative added to the flux of the present invention is less than 10% by mass, the pH of the flat residue cannot be maintained neutral or basic, so that the bonding strength in a high temperature and high humidity environment decreases. If the guanidine derivative added to the flux exceeds 30% by mass, the flux before soldering will be biased to basicity, resulting in an increase in solder balls. Therefore, the total amount of guanidine derivatives used in the present invention is preferably 10 to 30% by mass. Even more preferably, the amount of guanidine derivatives is 15 to 20% by mass in total.

In the present invention, in addition to the guanidine derivative, an amine that reacts at a relatively low temperature can be added to the solder paste flux as an amine. In addition to the guanidine derivative of the present invention, diamine, tripropylamine, dihexylamine, trihexyloleamine, decylamine, didecylamine, undecylamine, didecylamine, dodecylamine, didodecylamine, hexadecylamine, octadecylamine , Siku Examples include oral hexylamine, dicyclohexylamine, polyoxyethylene dicyclohexylamine, dimethylaniline, diphenylamine, and triphenylamine.

[0030] The guanidine derivative used in the present invention can prevent a decrease in solder joint strength at higher temperatures and higher humidity by coexisting with liquid paraffin or paraffin wax. Liquid paraffin or paraffin wax itself is neutral and, when added to the solder paste flux, hardly changes the pH of the flux residue. By adding liquid paraffin or paraffin wax to the solder paste flux, a layer that does not allow moisture to pass through is formed on the surface of the flux residue, and the solder alloy is prevented from being ionized by separating it from moisture and the solder alloy. Furthermore, it prevents the solder joint strength from decreasing at high temperature and high humidity. When added Caro liquid paraffin or paraffin wax to the present invention is preferably 5 to 20 mass ^_0/0 during the solder paste flux. Liquid paraffin or paraffin wax added to the present invention may be added alone or in combination.

[0031] The Sn-Zn lead-free solder has poor wettability, and in the present invention, the pH of the flux residue must be 7.0 to 11; When the amine hydrohalide generally used as a flux activator is used in the solder paste of the present invention, the ρ 残渣 of the flux residue increases (acidic region). Suitable as the activator of the present invention is that the pH in the flux is not biased to the acidic range! / Organic halogen compounds are suitable! /. Preferable examples of the organic halogen compounds include hexasuboxycyclodidecane, trans ns-2,3 dib-mouth mode 2 butene 1,4-diol, 2,3 dib-mouth mode 1,4 as aliphatic organic halogen compounds. There are butane diol, 2,3 dib mouth-moe 1 propanol, 1,3 dib mouth moe 2 propanol. Tris (2,3 dibromopropyl) isocyanurate is also suitable, although it is not an aliphatic organic halogen compound.

[0032] The addition of an organic halogen compound and an amine such as an aromatic amine or heterocyclic amine in the present invention can be expected to be effective even when added alone. Furthermore, by adding these at the same time, the shortcomings of the solderability of liquid paraffin and paraffin wax can be compensated and a synergistic effect can be expected.

Example As the Sn-Zn lead-free solder composition, the general Sn-3Bi_8Zn and Sn_9Zn compositions were used. Table 1 shows the flux composition.

1. Contains solder paste

Sn-3Bi-8Zn and Sn-9Zn solder powder ^{^{(2 0~ 4 0 μ m)}} 88 wt%

Flux (The composition is listed in Table 1) 12% by mass

Flux and solder powder were mixed to make a solder paste and its properties were compared. The test results of the examples and comparative examples are also shown in Table 1.

[table 1]

<BR>

[0034] 1.Flux residue pH test method

1.) Print the solder pastes of the examples and comparative examples on a 50 x 50 x 0.5 mm copper plate specified in JISH3100 using a metal mask with a 6.5 mm diameter hole. 2) Pre-heat temperature of test copper plate from 150 to 170; C, 90 seconds, peak temperature 220. C, 200. Reflow soldering under reflow conditions of C and 30 seconds, oxygen concentration 3000ppm.

3.) After standing to cool, scrape the residue with a spatula etc. and collect the residue.

4.) Boil a 1% aqueous solution of the collected residue, measure the pH after cooling.

[0035] 2. Shear strength test

1.) Mount a 1005 chip capacitor on the test board with a mounter.

2.) Preheat the test substrate to 150 ~; 170. C, 90 seconds, peak temperature 220. C, 200. Reflow soldering under the reflow conditions of C and 30 seconds, oxygen concentration 3000ppm.

3.) After allowing the test substrate to cool, measure the shear strength using a shear strength tester under conditions of test speed SOO ^ m / sec and test height 15 πι.

[0036] 3. Insulation degradation test

1.) Mount a 1608C capacitor (capacitance 1 a F, rated voltage 6.3V) on the test board with a mounter.

3.) After allowing the test board to cool, apply a voltage of 6.3V in an environment of 85 ° C / 85% RH and measure the insulation resistance up to 500h. The measurement voltage was 6.3V.

4.) Judgment criteria of insulation deterioration test were determined to be 1 X 107 Ω or less as a failure.

[0037] The solder paste of the present invention had a strength that hardly deteriorated the insulation resistance and hardly deteriorated even in an environment of 85 ° C and 85% RH. In contrast, the solder paste of the comparative example showed a decrease in strength and an insulation resistance in an environment of 85 ° C. and 85% RH.

Industrial applicability

[0038] The solder paste of the present invention can also be used for general lead-free solder alloys other than Sn-Zn-based lead-free solder pastes.

Claims

The scope of the claims

[1] A solder paste kneaded with Sn—Zn-based lead-free solder alloy powder and flux, characterized by containing 10-30% of a guanidine derivative as an amine in the flux

Sn—Zn-based lead-free solder paste.

[2] The derivatives of guanidine are 1,3 diphenyldanidine, 1,3 di-0-tolylguanidine.

2. The Sn—Zn-based lead-free sonoreda paste according to claim 1, which is 1-0-tolylbiguanide.

[3] The Sn—Zn-based lead-free solder paste according to claim 1 or 2, wherein the flux uses a halogen-free flux.

[4] In soldering using a solder paste in which Sn—Zn-based lead-free solder alloy powder and halogen-free flux are kneaded, the pH of the flux residue after soldering is 7 to 11 Sn—Zn-based lead-free solder paste soldering method.