JP2008270247A - Printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve solder connection reliability of a multilayer structure printed wiring board of a metal base or metal core type. <P>SOLUTION: The printed wiring board of a metal base or metal core type having a metal plate has a multilayer structure 3 configured by laminating a plurality of base materials 2 and metal wiring layers 1. This multilayer structure 3 is bonded on a metal plate 4 via a heat transfer insulating resin 5, and the base materials 2 of the multilayer structure 3 are each an epoxy resin and have a tensile elasticity of ≤400 MPa at -40°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal base or metal core type printed wiring board with improved solder joint reliability.

  Power boards used in vehicles that are required to operate in harsh environments, such as automobile engine rooms, require circuit operation in a high temperature environment. A metal core type printed wiring board is used. Furthermore, since automobiles must be able to operate in a wide range of environments from the extremely cold region to the tropical region and the operating environment is severe, the control board used in the engine room is not required for solder connection reliability of mounted components. Severely, for example, a reliability having a resistance of 3600 times or more in a −40 ° C./125° C. heat cycle may be required.

  Conventionally, it is known to improve the solder connection reliability of a mounted component by lowering the elastic modulus of a base material such as glass epoxy constituting a printed wiring board. For example, in Patent Document 1, by using a dimer acid-modified epoxy resin and a propylene oxide-added bisphenol A type epoxy resin component as an epoxy resin impregnated in glass cloth, the heat resistance, moisture resistance, and metal foil peeling strength of the base material are used. This shows a multilayer printed wiring board that can be reduced in elasticity while ensuring a low solder crack generation rate after 1000 cycles at -30 ° C / 120 ° C heat cycle.

  Further, a highly reliable metal base substrate in which a heat conductive silicone rubber having a low elastic modulus is formed on a metal base plate and a circuit is formed thereon is commercially available.

Japanese Patent Laid-Open No. 5-271442 (pages 2 to 3, Table 3)

  Since the printed wiring board as disclosed in Patent Document 1 is not a metal base or metal core type, the heat dissipation performance is low, and there is a high possibility that a problem that the circuit cannot operate in a high temperature environment may occur. In addition, a multilayer printed wiring board having a low solder crack generation rate after 1000 times at a -30 ° C./120° C. heat cycle is shown, but a metal base or metal core type printed wiring board with a large amount of solder deformation is used. In such a case, the rate of occurrence of solder cracks is greatly reduced, so that there is a problem that the solder joint reliability cannot be sufficiently ensured under a severe operating environment.

  Moreover, although the said commercially available metal base board has acquired the outstanding solder connection reliability, since the silicone rubber is used for insulating resin, multilayering is difficult.

  The present invention has been made to solve the above-described problems, and an object thereof is to improve the solder joint reliability of a printed wiring board having a multilayer structure and a metal base or metal core type.

  The printed wiring board according to the present invention is a metal base or metal core type having a metal plate and has a multilayer structure in which a plurality of base materials and metal wiring layers are stacked. This multilayer structure is bonded to a metal plate via a heat conductive insulating resin, the base material of this multilayer structure is an epoxy resin, and the tensile elastic modulus at −40 ° C. is 400 MPa or less.

  The present invention is a metal base or metal core type, and uses an epoxy resin composition (hereinafter referred to as epoxy resin) as a base material of a printed wiring board having a multilayer structure composed of a plurality of layers of metal wiring, and the epoxy resin. Since the tensile elastic modulus of the cured product is set to 400 MPa or less at −40 ° C., the solder joint reliability can be improved.

  Tensile modulus of elasticity (applied frequency: 1 Hz, hereinafter the same condition) of the base material (epoxy resin) used for the metal base substrate (or metal core substrate) at −40 ° C. and solder deformation of the component mounting part between −40 ° C. and 125 ° C. It was experimentally found that the amount (solder distortion) has a correlation, and FIG. 1 was obtained. The part whose solder distortion was measured was a 3225 resistor chip, and Sn-3Ag-0.5Cu was used as the solder.

  By applying an epoxy resin of 400 MPa or less at −40 ° C. as a base material to a metal-based or metal core type multilayer printed wiring board, the solder distortion ratio of the 3225 chip component mounting part at −40 ° C./125° C. heat cycle can be obtained. It was also found that the resistance was 5.0% or less, and resistance of 3600 cycles or more was obtained. FIG. 2 shows the solder distortion rate of a 3225 chip component mounting part in which an epoxy resin is mounted on a metal base or metal core type multilayer printed wiring board, and the yield rate of solder joints after 3600 cycles of −40 ° C./125° C. heat cycle. FIG. In addition, the point shown with the code | symbol A is a result of the printed wiring board of Embodiment 1 mentioned later.

Here, the quality determination after the heat cycle was such that the crack length (solder crack rate) per solder joint length in cross-sectional observation was less than 20%. When the solder distortion rate was 5.0% or less, the yield rate of solder joints was 100%. On the contrary, when the solder distortion ratio was 6.4% to 7.0%, the durability of 3600 cycles could not be obtained. Since a plurality of mounting components are mounted on the printed wiring board, solder mounting becomes a non-defective product in all mounting components, and the printed wiring board on which the components are mounted becomes a non-defective product. If n mounting parts are mounted at a non-defective product rate X%, the printed circuit board has a non-defective product rate of (X / 100) ⁿ × 100%. Therefore, it is required that the non-defective product rate of solder bonding in the mounted component is 100%. Therefore, if the solder distortion is 5.0% or less, a non-defective product can be obtained in a printed wiring board on which components are mounted. Hereinafter, preferred embodiments of the present invention will be described.

Embodiment 1 FIG.
3 is a cross-sectional view of a metal-based printed wiring board according to Embodiment 1 of the present invention. A multilayer structure 3 having six wiring layers in which a copper wiring 1 is insulated by an insulating resin 2 is bonded to an aluminum plate 4 which is a metal base via a heat conductive insulating resin 5. The multilayer structure 3 is formed with through holes 6A to 6E which are thermal vias. The thermal via is for improving heat dissipation characteristics, and copper plating is applied to the wall surface as a heat transfer film. Connection of copper wirings 1 of different layers in the multilayer structure 3 is made by wiring connection holes 7A to 7B which are through holes. For example, in the wiring connection hole 7B, the uppermost layer (first layer) copper wire 1A corresponds to the fourth layer copper wiring 1B and the sixth layer copper wiring 1C corresponding to the fourth and sixth layers from the uppermost layer, and the wiring connection hole 7B. It is connected with a metal such as copper plating applied to the inner surface of the metal.

  In order to efficiently dissipate heat from the semiconductor circuit component that generates high heat to the printed wiring board, the corresponding component is mounted on the printed wiring board so as to be disposed on the through holes 6A to 6E that are thermal vias. Since heat is radiated from the through holes 6A to 6E to the metal base, the thermal resistance is lowered as compared with the case where there is no thermal via, and the temperature around the semiconductor circuit component and the semiconductor circuit component mounted can be lowered. As a result, it is possible to prevent a problem that the semiconductor circuit component does not operate normally, or that the solder connection portion is cracked due to a temperature change caused by operation and stop of the device on which the control board is mounted.

  Next, a manufacturing method for the printed wiring board and characteristics of the manufactured printed wiring board will be described.

  First, the epoxy resin composition used as the insulating resin 2 will be described. MB7 (Japan Epoxy, dicyandiamide / bisphenol A type epoxy resin masterbatch) 5.8 parts, 2E4MZ (Shikoku Chemicals Co., Ltd. 2-ethyl-4-methyl) with 100 parts of Japan Epoxy YL-7217 2.5 parts of imidazole was diluted with PGMA (propylene glycol monomethyl ether acetate) so that the solid content was 60% by mass, and mixed and dissolved.

  The resulting resin composition was coated on the mat surface of an 18 μm thick electrolytic copper foil so that the dry thickness was 40 μm, and then heated in a 120 ° C. hot air oven for 10 minutes, and further in a 150 ° C. hot air oven for 3 minutes. It dried and the RCC (Resin Coated on Copper) sheet | seat was obtained.

  The obtained RCC sheet was cured by heat treatment at 150 ° C. for 1 hour and further at 180 ° C. for 1 hour. The copper foil of the RCC sheet after curing was etched. When the tensile viscoelasticity of the resin part after etching was measured, the elastic modulus at −40 ° C. was 177 MPa, and the glass transition point obtained from the Tan δ peak was −41 ° C.

  A 40 mm × 60 mm 6-layer printed wiring board was produced using an RCC sheet on which a wiring pattern was formed by etching. First, two RCC sheets are overlapped with each other to form two layers. The resin of the RCC sheet is a base material for the two-layer wiring and plays a role as the insulating resin 2. After that, a 6-layer printed wiring board was obtained in which the insulating resin 2 was placed between the wirings so that the wirings were exposed on the outer surface (front surface and back surface). A copper plate having the same size as the back surface (C surface) of the 6-layer printed wiring board was hot-press bonded with an alumina-containing high thermal conductive epoxy resin having a thermal conductivity of 1.5 Wm · K. The adhesion thickness between the copper plate and the copper foil wiring was about 40 μm.

  A total of 20 3225 capacitor chip components and 3225 resistor chip components in a direction perpendicular to the X-axis direction and the Y-axis direction were mounted on the obtained substrate by reflow. The solder was formed by printing Sn-3Ag-0.5Cu paste on a printed wiring board.

  The board on which the above components were mounted was put into an air tank heat cycle apparatus of −40 ° C. (30 minutes) / 125 ° C. (30 minutes), and a heat cycle test was performed. After 3600 cycles, the substrate was taken out and the cross section of the solder joint was observed. As a result, all 10 capacitors (20 solder joints) had a solder crack rate of less than 10%, and all 10 resistors (20 solder joints) had a solder crack rate of less than 15%. Judged to be non-defective. In addition, the solder distortion rate during the heat cycle, that is, between −40 ° C. and 125 ° C. was 3.5%, which is 5.0% or less.

  As described above, the metal-based multilayer printed wiring board according to Embodiment 1 has an elastic modulus of 400 MPa or less at −40 ° C. because the elastic modulus of the epoxy resin used for the base material is −40 ° C. and 125 ° C. The solder distortion ratio between them could be 3.5%. As a result, the solder crack rate was less than 15%, and the solder joint reliability could be improved.

  In addition, the manufacturing method of the printed wiring board of the multilayer structure mentioned above is an example, Comprising: It is not limited to this. In addition, although the metal-based multilayer printed wiring board in which the wiring is arranged on one side of the metal plate has been described, the wiring is arranged on both sides of the metal plate so that the metal core type multilayer structure is provided. It can also be applied to printed wiring boards.

It is a figure which shows the elastic modulus of an epoxy resin base material, and the solder distortion rate in a heat cycle. It is a figure which shows the solder distortion rate of an epoxy resin base material, and the non-defective rate of the solder joint after a heat cycle test. It is sectional drawing of the metal-based printed wiring board in Embodiment 1 of this invention.

Explanation of symbols

1, 1A, 1B, 1C Copper wiring 2 Insulating resin 3 Multilayer structure 4 Aluminum plate 5 Thermal conductive insulating resin 6A, 6B, 6C, 6D, 6E Through-hole

Claims (2)

A metal base or metal core type printed wiring board having a metal plate,
Adhered to the metal plate via a heat conductive insulating resin, and having a multilayer structure configured by stacking a plurality of base materials and metal wiring layers,
The printed wiring board, wherein the substrate is an epoxy resin and has a tensile elastic modulus at −40 ° C. of 400 MPa or less. A through hole penetrating a plurality of layers of the epoxy resin base material on which the metal wiring layer is formed is formed, a heat transfer film is formed on a wall surface of the through hole, and heat is conducted to the metal plate through the through hole. The printed wiring board according to claim 1.

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