Flux for soldering and circuit board

a circuit board and soldering technology, applied in the field of flux, can solve the problems of affecting the electrical insulation properties between the lands, affecting the bonding strength of soldering, and liable to liberate and deposit independently of silver or copper, so as to suppress the diffusion of nickel, improve the bonding strength of soldering, and suppress the reduction deposition of silver and/or copper

Inactive Publication Date: 2006-07-06
HARIMA CHEM INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0008] One advantage of the present invention is to improve the bonding strength of soldering by suppressing the diffusion of nickel into the melted solder alloy during soldering, and to suppress the reduction deposition of silver and / or copper to portions other than a circuit pattern.
[0009] A flux of the present invention is particularly used when soldering is performed onto a circuit having electroless nickel plating or further having gold plating on the electroless nickel plating, and contains resin having film forming ability, activator, solvent, and at least one complex selected from silver complex and copper complex. In the present invention, the term “complex” means silver or copper compound having at least one coordinate bond.
[0010] The complex in the present invention has no possibility that when heating this, silver or copper independently causes reduction deposition. Instead, the complex deposits due to the substitution by metal that is large in ionization tendency, namely nickel. Hence, it is able to form a barrier layer of silver and / or copper only on the surfaces of the lands, without possibility of forming a thin metallic film between conductor patterns of a substrate, and impairing electrical insulating properties between the lands. The barrier layer of silver and / or copper so formed on the surfaces of the lands suppresses the diffusion of nickel into solder alloy, and prevents the formation of a phosphorous concentrated layer, thereby to improve the bonding strength of the solder.
[0011] In other words, a circuit board of the present invention includes lands having on their surfaces electroless nickel plating or further having gold plating on the electroless nickel plating, and a barrier layer of at least one selected from silver and copper to be formed on the surfaces of the lands.
[0012] The present invention is also effective in the surface further having gold plating on electroless nickel plating, not only the case of a direct soldering to an electroless nickel plating layer. Specifically, although during soldering, gold plating coat diffuses momentarily into solder alloy, and nickel and solder alloy make direct contact to form the above-mentioned phosphorous concentrated layer, the present invention can prevent this effectively.
[0013] In the present invention, silver or copper is substituted by nickel and deposited due to heating at the time of soldering, thus enabling to form a barrier layer on the surfaces of the lands. Therefore, preferably, the complex of the present invention does not cause substitution deposition of silver and copper at temperatures of less than 150° C., and initiates substitution deposition when the temperature is elevated to not less than 150° C. during soldering. Further, the complex preferably does not cause metal deposition at portions other than the circuit pattern at temperatures of not more than 280° C., at which it might be exposed during soldering.

Problems solved by technology

Unfortunately, when the salts of silver and copper are used as additives to flux, silver or copper is liable to liberate and deposit independently.
Since the metallic film cannot be removed by cleaning, there arises the problem of impairing electrical insulating properties between the lands.

Method used

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  • Flux for soldering and circuit board
  • Flux for soldering and circuit board
  • Flux for soldering and circuit board

Examples

Experimental program
Comparison scheme
Effect test

examples

[Silver or Copper Compound]

[0066] As silver or copper compounds, the following materials were selected. [0067] A: [Ag{P(C6H5)3}4]+CH3SO3−[0068] B: [Ag]+C6H4N3−[0069] C: [Ag]+C2H2N3S−[0070] D: [Cu{P(C6H5)3}3]+CH3SO3−[0071] E: [Cu]+C6H4N3−[0072] F: [Cu]+C2H2N3S−

experimental example 1

[0077] The respective fluxes in Table 1 were printed overall and in a thickness of 100 μm on a tandem-pattern substrate, and heated by using reflow profile whose maximum temperature was 250° C. The substrate was then immersed in an ultrasonic washer filled with butyl carbitol solution of 60° C., to remove the flux. Then, insulating resistance was measured after leaving it for 168 hours in an atmosphere having a temperature of 85° C. and a relative humidity of 85%, while applying a voltage of DC50V to the substrate (Based on the test method of JIS Z3197).

experimental example 2

[0078] Lands were formed on a substrate, which were 0.4 mm in diameter and had nickel electroless plating to copper and further had gold flash plating thereon, and the respective fluxes in Table 1 were printed overall and in a thickness of 100 μm on the substrate. Then, solder balls of tin-37 lead having a diameter of 0.4 mm were placed on the lands, and allowed to reflow at 220° C. so as to connect the solder balls to the lands. Subsequently, the substrate was immersed in an ultrasonic washer filled with butyl carbitol solution of 60° C., to remove the flux.

[0079] Thereafter, with regard to resist portions in the vicinity of en electrode pattern, elemental analysis with an energy dispersive X-ray fluorescence analyzer (EDX) was conducted to examine the presence or absence of the reduction deposition of the metal of silver or copper.

[0080] In addition, with regard to the soldered portions of the soldered substrate, tension test was conducted to measure bonding strength (DAGE-SERIE...

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Abstract

A flux contains resin having film forming ability, activator, solvent, and at least one complex selected from silver complex and copper complex. The flux is used when soldering is performed onto a circuit having electroless nickel plating or further having gold plating on the electroless nickel plating. Allowing a barrier layer of silver or copper to deposit on the surfaces of lands suppresses the diffusion of nickel into the melted solder alloy during soldering, and also prevents phosphorous concentration. This improves the bonding strength of soldering and suppresses the reduction deposition of silver and/or copper to portions other than circuit patterns.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a flux used when soldering various electronic components onto a circuit board, and more particularly to a flux used when soldering is conducted onto copper lands having electroless nickel plating or further having gold plating on the electroless nickel plating, as well as a circuit board. [0003] 2. Description of Related Art [0004] Traditionally, when electronic components are generally soldered onto a printed circuit board, soldering to copper lands formed on the printed circuit board has been done by using tin / lead alloy solder and lead-free solder. Generally, to prevent copper oxidation, electroless nickel plating to the surfaces of the lands is conducted in advance, and gold plating to the surface is further conducted in advance by using a nickel plating layer as a barrier layer. [0005] However, since hypophosphite is used as reducing agent in the electroless nickel plating to th...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B32B3/00C22B9/10
CPCH05K3/244Y10T428/24917H05K2203/121H05K3/3489
Inventor IKEDA, KAZUKIISHIKAWA, SHUNSUKEANADA, TAKAAKIOBATA, KEIGOTAKEUCHI, TAKAOINOUE, NAOYA
Owner HARIMA CHEM INC
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