JP2006100447A - Wiring board with lead pin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, when a lead pin is joined with an end surface of a through conductor of a wiring board made of glass ceramic via an active metal containing Ag-Cu alloy brazing filler, low melting metal such as silver or copper included in the conductor diffuses into the active metal containing Ag-Cu brazing filler to cause a void in the through conductor to have continuity resistance of the conductor increased. <P>SOLUTION: A wiring board with a lead pin includes an insulation substrate 5 made of glass ceramic, the through conductor 7 formed on the insulation substrate 5 and mainly containing copper or silver, and the lead pin 1 bonded to one of end surfaces of the conductor 7 and containing at least one of iron, nickel and cobalt. The lead pin 1 is bonded to the through conductor 7 via a connection pad 2 made of an Ag-Cu alloy filler containing at least one of Ti, Zr and Hf. The through conductor 7 has a diffusion preventive layer 10 formed on one of end surfaces, comprising at least one of a Ni layer and an Au layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a so-called pin grid array (PGA) in which lead pins for input / output terminals are erected, which are used for a semiconductor element housing package, a circuit board, an electronic circuit module, etc. for housing semiconductor elements. The present invention relates to a wiring board with lead pins.

  Conventionally, a semiconductor element housing package for housing a semiconductor element such as a semiconductor integrated circuit element such as an IC or LSI, a circuit board or an electronic circuit module constituting a high-frequency circuit or a power circuit, etc. are made of ceramics. A wiring board having a wiring conductor on at least one of the surface and the inside of an insulating base is used. In general, this wiring board is used to airtightly accommodate a semiconductor element inside a container composed of a terminal member such as a lead pin and a ball terminal, a heat radiating member such as a heat radiating plate and a heat radiating fin, and a wiring board and a lid. A metal member such as a seal member such as a seal ring for attaching a metal lid is joined to a wiring conductor made of a metallized layer on the surface of the wiring board via a brazing material.

  In the above wiring board, in order to transmit a high-frequency signal at a high speed, the resistance of the conductor forming the wiring conductor is required to be low, and the insulating base is also required to have a lower dielectric constant.

  For example, a wiring board in which glass ceramics having a low dielectric constant and suitable as an insulating base for high frequencies is used as an insulating base, and a metallized layer of a low resistance metal such as copper (Cu) or silver (Ag) is used as a wiring conductor is widely used. Has been.

  However, in such a high-frequency wiring board, glass ceramics with a low dielectric constant contain a large amount of glass components, so the porcelain strength thereof is lower than that of conventional alumina ceramics, etc., and copper that is a wiring conductor is used. Since a low resistance metal such as silver is also a low melting point metal, it is necessary to sinter at a low temperature. Therefore, the bonding strength of the wiring conductor composed of the metallized layer to the glass ceramic is low.

  Therefore, when a lead grid is bonded to an electrode pad manufactured using such metallization of a wiring board via a brazing material to form a wiring board with a pin grid array type lead pin, the wiring board is mounted on an external electric circuit. To insert the lead pin into the socket of the external electric circuit, or when the lead pin is pulled out because maintenance such as failure or replacement is necessary after mounting the wiring board on the external electric circuit, When this external force is applied, there is a problem that fracture stress is generated at the interface between the glass ceramic as the insulating substrate and the electrode pad, the electrode pad is peeled off and the bonding reliability is lowered.

  Therefore, as a technique for avoiding breakage at the interface between the insulating substrate such as glass ceramics having weak porcelain strength and the electrode pad, an Ag—Cu alloy brazing material containing at least one of Ti, Zr and Hf as an active metal is used. In a region including a portion where a through conductor (via conductor) as a wiring conductor led out from the inside of the wiring board to the lower surface is exposed on the surface of the insulating base without forming an electrode pad for lead pin bonding on the wiring board, A configuration for directly joining lead pins has been proposed.

  In this configuration, the portion exposed to the surface of the insulating base of the through conductor, which is a part of the wiring conductor, and the lead pin are not interposed via the electrode pad via the brazing material pad made of the active metal-containing Ag—Cu alloy brazing material. By making direct connection, electrical connection can be made. In addition, since the exposed portion of the through conductor is usually small in diameter of about 100 μm or less because the wiring density is increasing, the lead pin is substantially bonded to the insulating substrate and the brazing material pad. The lead pin can be bonded without depending on the bonding strength between the electrode pad and the insulating substrate, and the breakage at the interface between the insulating substrate and the electrode pad can be avoided.

Without passing through the electrode pad, the part exposed to the surface of the insulating base of the through conductor, which is a part of the wiring conductor, and the lead pin are directly connected via the brazing material pad made of the active metal-containing Ag—Cu alloy brazing material. In the joining method in which electrical connection is performed by connecting, the active metal-containing Ag—Cu alloy brazing material is printed and formed by a screen printing method or the like so as to cover the through conductor exposed on the surface of the wiring board. Lead pins are erected on the active metal-containing Ag—Cu alloy brazing material, and then heat treatment is performed at 800 to 1000 ° C. to join the lead pins to the wiring board.
JP-A-8-162563 JP-A-8-298381 JP-A-9-18144

  However, since the brazing filler metal pad of the active metal-containing Ag—Cu alloy brazing material is an alloy of copper and silver, the melting point is lower than that of single composition copper or silver forming the through conductor. Therefore, when the active metal-containing Ag—Cu alloy brazing material is heated and melted, the single composition of copper or silver forming the through conductor exists as a solid phase. As a result, the solid phase is diffused and moved from the through conductor to the active metal-containing Ag—Cu alloy brazing material side at the interface between the active metal-containing Ag—Cu alloy brazing material and the through conductor in such a form that it melts into the liquid phase. . As a result, voids are generated in the part where the copper or silver of the through conductor has diffused and moved.

  Further, when copper or silver having a single composition forming the through conductor diffuses into the connection pad in this way, the copper of the active metal-containing Ag—Cu alloy brazing material is present in the vicinity of the through conductor and other portions in the connection pad. And silver composition ratios are different. For example, when the through conductor is copper, the proportion of copper in the active metal-containing Ag—Cu alloy brazing material is larger in the vicinity of the through conductor of the connection pad than in other portions. As a result, the silver and copper composition of the active metal-containing Ag—Cu alloy brazing material shifts from the eutectic composition to the copper side. Therefore, a copper-rich solid solution (Cu phase) is formed as the primary crystal in the cooling process after melting, and this Cu phase grows and becomes coarse until the eutectic temperature is reached.

  For this reason, the contact area between the Cu phase and the Ag phase is smaller in the vicinity of the through conductor of the connection pad than in other parts where the primary crystal is not coarsened, and the binding energy between silver and copper is reduced. Becomes smaller. Therefore, there is a problem that the interface between the Cu phase and the Ag phase becomes brittle near the through conductor of the brazing material pad.

  For the above reason, at the fragile interface formed, the interface easily slips due to externally applied stress, and cracks are generated starting from the slip surface.

  Due to the voids inside the through conductors and cracks inside the connection pads generated due to the above reasons, the conduction resistance increases, and when it becomes prominent, there is a problem that the through conductors and the lead pins are insulated.

  The present invention has been completed in order to solve the above-mentioned problems. The purpose of the present invention is, for example, that a low-resistance metal such as a single composition copper or silver forming a through conductor is active during brazing. It does not diffuse into the metal-containing Ag-Cu alloy brazing material, the conduction resistance value of the through conductor increases, or cracks occur in the active metal-containing Ag-Cu alloy brazing material after long-term use. An object of the present invention is to provide a highly reliable wiring board with lead pins that can prevent insulation.

  The wiring board of the present invention includes an insulating base made of glass ceramics, a wiring conductor formed on the surface of the insulating base, a through conductor mainly composed of copper or silver formed through the insulating base, A lead pin containing at least one of iron, nickel, and cobalt joined to one end face of the through conductor, and the lead pin contains Ag—Cu containing at least one of Ti, Zr, and Hf In the wiring board with lead pins joined to the through conductor via a brazing filler metal pad, the through conductor has a diffusion prevention layer formed of at least one of an Ni layer or an Au layer on the one end surface. It is characterized by.

  The wiring board of the present invention is preferably characterized in that the diffusion preventing layer has a thickness of 1 μm to 20 μm.

  According to the wiring board with lead pins of the present invention, the lead pins are joined to the through conductors via the connection pads made of an Ag—Cu alloy brazing material containing at least one of Ti, Zr and Hf. In addition, since the diffusion prevention layer made of at least one of the Ni layer and the Au layer is formed on one end surface, the through conductor contains the active metal by the diffusion prevention layer during the heat treatment for standing and joining the lead pins. Since it is structurally cut off from the Ag-Cu alloy brazing material, copper and silver having a single composition forming through conductors do not diffuse into the active metal-containing Ag-Cu alloy brazing material and contain active metal. When the coarse Cu phase or Ag phase is generated in the vicinity of the through conductor of the Ag—Cu alloy brazing filler metal, it is possible to suppress the fragile interface between silver and copper. As a result, voids are formed in the through conductor and the conduction resistance value of the through conductor is increased, or when a large external force is applied, a crack is generated in the active metal-containing Ag-Cu alloy brazing material, and the through conductor and the lead pin are insulated. This can be prevented.

  In the wiring board with lead pins of the present invention, preferably, the diffusion prevention layer has a thickness of 1 μm to 20 μm, so that the conduction resistance is more effectively increased between the through conductor and the lead pin, and both are insulated. Can be prevented.

  The wiring board with lead pins of the present invention will be described in detail below. FIG. 1 is a cross-sectional view showing an example of an embodiment in which the wiring board with lead pins of the present invention is applied to a semiconductor element housing package for housing semiconductor elements. In FIG. 1, 1 is a lead pin, 2 is an active metal-containing Ag—Cu alloy brazing material pad (hereinafter also referred to as a brazing material pad) as a connection pad, and 3 is a wiring substrate with lead pins (hereinafter also referred to as a wiring substrate), 4 Is a semiconductor element. The insulating substrate 5 made of glass ceramics of the wiring board 3 has a mounting portion 8 for mounting the semiconductor element 4 at the center of the upper surface. Reference numeral 10 denotes a diffusion prevention layer between the through conductor and the connection pad.

  The insulating base 5 is, for example, a rectangular plate-like body made of a glass ceramic sintered body, and has a wiring conductor 6 on at least one of its surface and inside.

The insulating base 5 made of glass ceramics in such a wiring board 3 is manufactured as follows, for example. First, as a glass component, SiO ₂ —B ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ system, SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —MO system (where M is Ca, Sr, Mg, Ba or Zn), SiO ₂ —Al ₂ O ₃ —M ¹ O—M ² O system (where M ¹ and M ² are the same or different, and Ca, Sr, Mg, Ba or Zn), SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —M ¹ O—M ² O system (where M ¹ and M ² are the same as above), SiO ₂ —B ₂ O ₃ — M ³ ₂ O system (where M ³ represents Li, Na or K), SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —M ³ ₂ O system (where M ³ is the same as above) , PB glass, Bi glass, etc., and Al ₂ O ₃ , SiO ₂ , Z a composite oxide of rO ₂ and an alkaline earth metal oxide, a composite oxide of TiO ₂ and an alkaline earth metal oxide, a composite oxide containing at least one selected from Al ₂ O ₃ and SiO ₂ (spinel) , Mullite, cordierite, etc.) filler powder in a mass ratio of 40:60 to 99: 1, and further, an appropriate organic solvent and solvent are added and mixed to form a mud, which is a doctor blade. A ceramic green sheet (ceramic green sheet) is obtained by forming into a sheet by the method of calendering or calendering.

  Next, on this ceramic green sheet, a conductor paste obtained by pasting a powder of a conductor material is printed by a screen printing method or a gravure printing method, or a method such as transferring a metal foil having a predetermined pattern shape, A wiring conductor 6 is formed. As the conductive material of the conductive paste, Cu, Ag, Ag—Pt, Ag—Pd, Au, or the like is suitably used for the glass ceramic sintered body.

  The wiring conductor 6 also includes a through conductor 7 such as a via conductor or a through-hole conductor for connecting the conductor patterns respectively disposed on the upper surface and the lower surface of the insulating substrate 5 inside the insulating substrate 5. . The through conductor 7 is formed, for example, by filling a through hole formed in the ceramic green sheet by punching or the like with a conductor paste.

  The wiring conductor 6 is mainly formed on the surface of the insulating substrate 1, and a part of the wiring conductor 6 functions as an electrode pad 9 for electrically connecting the electrodes of the semiconductor element 4.

  Next, a plurality of ceramic green sheets on which a conductive paste to be the wiring conductor 6 and the through conductor 7 is formed are laminated and fired at a predetermined temperature (about 900 ° C. in the case of glass ceramics), whereby the wiring substrate 3 The portions of the insulating base 5 and the wiring conductor 6 are manufactured.

  Next, as shown in a cross-sectional view in FIG. 2, in order to form the diffusion prevention layer 9 on the surface exposed to the surface of the insulating base 5 of the through conductor 7, a Ni layer or Au is formed by plating, vapor deposition, sputtering, or the like. Form a layer. Compared with metals such as Co and Pt, the Ni layer has good adhesion to copper and silver and is difficult to diffuse, so it effectively functions as a diffusion preventing layer. Moreover, since Au is a metal element that is more difficult to diffuse with respect to copper and silver, the diffusion of copper and silver can be more effectively prevented by providing a single Au layer.

  The thickness of the diffusion preventing layer 10 is preferably 1 μm to 20 μm. When the thickness of the diffusion preventing layer 10 is less than 1 μm, defects such as pinholes occur because the thickness is small. For this reason, when the heat treatment for attaching the lead pin 1 is performed, the low resistance metal such as copper and silver contained in the through conductor diffuses from the defect portion into the active metal-containing Ag-Cu alloy brazing material (brazing material pad 2), A brittle layer is generated by forming a coarse Cu phase or Ag phase in the active metal-containing Ag-Cu alloy brazing material.

  Further, when the thickness of the diffusion preventing layer 10 exceeds 20 μm, Ni and Au constituting the diffusion preventing layer 10 have a large elastic coefficient, so that a large stress is generated when an external force is applied by the amount of the increased thickness. Therefore, there arises a problem that the diffusion preventing layer 10 is easily broken even with a relatively small external force.

  An example of forming Ni and Au by plating is shown below. The Ni plating layer is composed of an electroless Ni—P plating layer containing about 4 to 12% by mass of P. In such a Ni plating layer, first, the insulating base 5 on which the wiring conductor 6 and the through conductor 7 are formed is immersed in an acidic cleaning solution having a temperature of 25 to 50 ° C. composed of a surfactant and a hydrochloric acid aqueous solution for 1 to 5 minutes. Then, the surface exposed on the surface of the through conductor 7 is cleaned and then washed with pure water, and then the palladium activity at a temperature of 25 to 40 ° C. composed of palladium chloride, potassium hydroxide, ethylenediaminetetraacetic acid is obtained. Immerse in the solution for about 1 to 5 minutes to attach the palladium catalyst to the surface exposed on the surface of the through conductor 7, and then wash it with pure water, then nickel sulfate, sodium citrate, sodium acetate, The surface exposed to the surface of the through conductor 7 is immersed in an electroless Ni plating solution of sodium phosphite and ammonium chloride at a temperature of 50 to 90 ° C. for 2 to 60 minutes. It is wearing.

  Then, a conductor paste containing an active metal-containing Ag—Cu alloy brazing material is printed by a screen printing method, a gravure printing method, or the like in a region including a portion where the through conductor 7 on the lower surface of the wiring board 3 is exposed on the surface of the insulating substrate 5. Then, the lead pin 1, the surface exposed to the surface of the through conductor 7 of the wiring board 3, and the insulating base 5 including the surface are brazed via a brazing material pad made of an active metal-containing Ag—Cu alloy brazing material. . The active metal-containing Ag-Cu alloy brazing material used as the brazing material pad is composed of BAg-8 (JIS Z-3261: 72 mass% Ag-28 mass% Cu) brazing material, and Ag is 60 to 80 mass%. At least one of active metals Ti, Zr, and Hf is added to an Ag—Cu alloy brazing material having a composition of Cu of 20 to 40% by mass in the form of metal or hydride in an amount of 2 to 10% by mass. Those added are preferably used.

  In order to join the lead pin 1 to the insulating base 5 via the brazing material pad 2, an organic solvent, a resin binder, and a solvent (organic solvent, water, etc.) are combined with the powder of the active metal-containing Ag—Cu alloy brazing material 5 A predetermined pattern corresponding to a portion where the lead pins 1 are erected by screen printing or the like on the surface of the insulating substrate 5 including the end face where the through conductors 7 are exposed. The head portion 1a of the lead pin 1 is placed on this, and a predetermined temperature (for example, about approximately) is set in accordance with the melting temperature of the active metal-containing Ag—Cu alloy brazing material in a vacuum, a neutral atmosphere or a reducing atmosphere. 800 ° C.), the active metal-containing Ag—Cu alloy brazing material is melted, and the wiring conductor 6 and the insulating base 5 are joined to the lead pin 1 by brazing.

  At this time, considering the melting point of the active metal-containing Ag—Cu alloy brazing material, the appearance of the joint after brazing, the thickness of the reaction layer and the alloy layer, etc., the active metal content, volume ( Volume), the maximum brazing temperature, the holding time at a temperature equal to or higher than the melting point of the brazing pad 2 must be determined.

As an example, a brazing material in which 3% by mass of TiH ₂ is added as an active metal to a so-called BAg-8 brazing material of 72% by mass Ag-28% by mass Cu is used, and the diameter after brazing on the surface of the insulating substrate 5 When a 0.90 mm connection pad is formed, a nail head type lead pin 1 having a pin diameter of 0.20 mm, a head portion 1a thickness of 0.15 mm, and a head portion 1a diameter of 0.45 mm is provided on the insulating substrate 5 in a predetermined manner. A good bonding state having a high bonding strength can be obtained by holding at a maximum temperature of 795 ° C. to 850 ° C. for 5 minutes to 1 hour in a state of contact with the part.

Here, when the insulating substrate 5 is made of glass ceramics is a thermal expansion coefficient at 40 to 400 ° C. is ^{2.3 × 10 -6 /℃~4.5×10 -6 / ℃} , and the side of the head portion 1a It is preferable that the distance between the outer peripheral edge of the brazing pad 2 is 0.125 mm or more over the entire circumference.

  The material of the lead pin 1 used in the wiring board 3 of the present invention, the length of the pin portion, the thickness of the head portion 1a, and the like can be selected according to the shape of the socket of the external electric circuit, the connection method, and the like. For example, in the case of a lead pin 1 applied to a package for housing a semiconductor element, one made of an Fe-Ni-Co alloy or Cu alloy is used, and a pin having a length of about 1 to 6 mm is used. The

By joining the lead pin 1 and the insulating base 5 as described above, the lead pin 1 is joined to the through conductor 7 via the brazing material pad 2, and an increase in the conduction resistance between the through conductor 7 and the lead pin 1 is suppressed. It is possible to obtain the wiring substrate 3 with lead pins capable of preventing the through conductors 7 and the lead pins 1 from being insulated.

  Examples of the wiring board with lead pins of the present invention will be described below.

First, SiO ₂ having an average particle diameter of 2 μm is used as the glass powder, cordierite having an average particle diameter of 1 to 2 μm is used as the filler powder, and the mixture is mixed at a mass ratio of 40:60, and further suitable organic A solvent and a solvent were added and mixed to form a slurry, which was formed into a sheet by a doctor blade method or a calender roll method to produce a ceramic green sheet (ceramic green sheet).

  Next, through holes were formed in this ceramic green sheet by punching, and a via conductor was formed by filling a conductor paste obtained by pasting Cu powder.

  Next, a conductor paste obtained by pasting Cu powder was printed by a screen printing method to form a wiring conductor (a conductive paste layer serving as a wiring conductor).

  Next, a plurality of ceramic green sheets having these via conductors and wiring conductors were laminated and fired at a temperature of 950 ° C. to produce an insulating base made of glass ceramics.

  Next, in order to form the diffusion prevention layer 10 on the surface exposed to the surface of the insulating base 5 of the through conductor 7, a Ni layer and an Au layer were sequentially laminated by a plating method.

Next, on the surface of the insulating substrate 5, 3% by mass of TiH ₂ as an active metal and 10% by mass of a resin binder are added to an Ag—Cu alloy brazing material (BAg-8) composed of 72% by mass of Ag and 28% by mass of Cu. An active metal-containing Ag—Cu alloy brazing paste externally added at a ratio is screen-printed as a brazing filler pad 2 for joining the lead pin 1 and the insulating base 5 to a diameter of 0.90 mm after brazing. A material pad 2 was formed.

  Next, through this brazing material pad 2, the diameter of the pin portion is 0.20mm, the thickness of the head portion 1a is 0.15mm, and the diameter of the head portion 1a is 0.45mm. The lead pin 1 was joined by maintaining a maximum temperature of 800 ° C. for 15 minutes in a vacuum furnace.

  By joining the lead pin 1 and the insulating base 5 as described above, the lead pin 1 is joined to the through conductor 7 via the connection pad 2, and an increase in the conduction resistance between the through conductor 7 and the lead pin 1 is suppressed. A wiring board 3 with a lead pin capable of preventing the through conductor 7 and the lead pin 1 from being insulated was obtained.

  In the wiring board 3 with lead pins, the total length of the lead pins 1 is 2.0 mm, the interval between the lead pins 1 is 2.0 mm, the diameter φ of the through conductor 7 is 100 μm, the length is 1.0 mm, and the electrode pad Reference numeral 9 is formed of a copper metallized layer, and 10 evaluation samples made of a rectangle having a thickness of 10 to 15 μm and an outer shape of 1.0 mm × 2.5 mm were produced.

  In addition, as a comparative example, ten wiring boards with lead pins (comparative samples) having the same dimensions and shape as the example products but not having the diffusion prevention layer 10 were produced in the same manner.

The resistance between the adjacent lead pins 1 of these wiring boards was measured with a digital multimeter, and the resistance value was measured. The measurement results are shown in Table 1.

  From Table 1, when the diffusion prevention layer 10 was formed, the conduction resistance between the lead pins 1 was reduced by about 63% on average as compared with the evaluation sample without the diffusion prevention layer 10 formed.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention. For example, in the above-described embodiment, an example in which the wiring board of the present invention is applied to a package for housing semiconductor elements has been described. However, it may be applied to other uses such as a hybrid integrated circuit board.

It is sectional drawing which shows the example of embodiment of the wiring board with a lead pin of this invention. It is a principal part expanded sectional view of the wiring board with a lead pin shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lead pin 1a ... Head part 2 ... Brazing material pad 3 ... Wiring board 4 with a lead pin ... Semiconductor element 5 ... Insulation base 6 ... Wiring conductor 7 ... Through-conductor 8 ... Mounting part 9 ... Electrode pad 10 ... Diffusion prevention layer

Claims (2)

An insulating base made of glass ceramics, a wiring conductor formed on the surface of the insulating base, a through conductor mainly composed of copper or silver formed through the insulating base, and an end face of the through conductor A lead pad containing at least one of iron, nickel and cobalt joined to the joint, the lead pin comprising an Ag-Cu alloy brazing material containing at least one of Ti, Zr and Hf A lead pin having a lead pin bonded to the through conductor via a lead pin, wherein the through conductor has a diffusion prevention layer formed of at least one of a Ni layer and an Au layer formed on the one end surface. With wiring board. The wiring board with lead pins according to claim 1, wherein the diffusion preventing layer has a thickness of 1 μm to 20 μm.

Images