JPS6214490A - Substrate for pga - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a PGA (pin grid array) substrate used as a packaging material for highly integrated devices.

[Prior Art and Problems] Currently, substrate materials on which highly integrated circuit elements can be directly mounted include organic materials such as glass epoxy and polyimide, and ceramic materials. These materials have excellent electrical insulation properties and can be mass-produced, so they have been widely used for PGA substrates, multilayer wiring boards, hybrid IC substrates, and the like. However, recently, ICs have become more highly integrated, and there are also plans for multi-chip ICs that mount multiple elements on a single substrate, making it difficult to ensure sufficient IC reliability using conventional materials. It became.

There are three important requirements for a substrate on which highly integrated devices are mounted: (1) high heat dissipation, (2) matching of thermal expansion coefficients, and (3) high frequency characteristics. Among these, high heat dissipation and consistency of thermal expansion coefficients are particularly important requirements related to ensuring reliability, but the conventional materials described above do not completely satisfy the requirements of device design names. This is because the amount of heat generated by the mounted elements is greater than the heat dissipation rate of the device, which increases the temperature inside the device, and strain stress is added to the silicon element due to the difference in thermal expansion coefficient between the silicon element and the substrate material. .

In response to the trend towards higher integration and higher density packaging, the application of metals to substrate materials has recently attracted attention. This attempts to take advantage of the inherent high heat dissipation of metals, but the biggest difficulty in this case is electrical insulation. Coefficient of thermal expansion is also a problem, and perfect matching of coefficients of thermal expansion requires the use of expensive materials such as molybdenum and tungsten, which do not have very good heat dissipation properties. 81 summarizes the 1h properties of various substrate materials.

Note that Teflon in the above table is a trade name of DuPont (USA) and is a typical tetrafluoroethylene resin, but there are no examples of it being used as a substrate material, and it is shown for reference only.

Among metal substrate materials, the inventors particularly focused on Cl0 (copper/invar/copper clad material). The reason is that it is possible to change the ratio of CIC's three-layer V4 structure, which is a so-called heat dissipation design, and it is also possible to utilize the properties of copper, which has high heat dissipation properties. There is already a plan to use CIC as a substrate material, but when using this material, there are issues with insulation treatment methods,
There are problems with surface treatment, including the cut surfaces of the three-layer collapsed clad shrine, and it has not yet been fully put into practical use.

[Object of the Invention] In view of the above-mentioned circumstances, the object of the present invention is to provide a highly reliable, highly integrated, and high-density mounting PGA substrate by subjecting CIC to special surface treatment and insulation treatment. be.

[Summary of the Invention] In other words, the present invention roughens the surface of a substrate made of copper/invar/copper cladding material having lead pin insertion holes, and coats the surface of the substrate on this roughened plating surface except for the heat dissipating portion of the substrate. Then, apply a coating of ethylene resin to the resin coating, form a desired circuit pattern with copper foil on this resin coating, provide a number of electrodes on this circuit pattern, and insert a lead pin from this number of electrodes into the insertion hole. It is constructed by coating a polytetrafluoroethylene resin with a low dielectric constant on the roughened plating surface to achieve high reliability.
This is a substrate for GA.

The reason why tetrafluoroethylene resin is used as the insulation treatment material in the present invention is its dielectric constant.

In addition to higher integration, the trend in ICs is toward higher speeds, and the dielectric constant of the insulating material of the substrate is directly related to this higher speed.

Generally, the delay time of a high frequency signal is expressed by the following formula.

To −12Co Zo =1-2 za=J'E ding'CO'7 (K/fi lower) d/ωTo
: delay time, 1: wiring length, CO: capacitance, Zo: impedance, Lo: inductance, εr: dielectric constant,
ω: wiring width, d: insulation layer thickness.

For this reason, the insulating material is required to have a low dielectric constant, and in the present invention, a tetrafluoroethylene resin such as Teflon, which has a low dielectric constant among organic materials, is selected. Although Teflon has low thermal conductivity as shown in Table 1, heat dissipation is achieved by CIC. Teflon is officially a tetrafluoroethylene-hexafluoropropylene copolymer, or other promising tetrafluoroethylene resins include tetrafluoroethylene alkyl vinyl ether copolymer,
Examples include ethylene-tetrabutylene copolymer.

[Example] Next, an example of the PG△ tool plate of the present invention will be described with reference to the accompanying drawings.

Example 1 The surface of a PGA substrate is not shown in FIG. 1 is a substrate made of copper/invar/copper clad material, 2 is copper, and 3 is invar. 4 is a lead pin insertion hole provided to penetrate the substrate 1. The thickness ratio of copper, invar, and copper in the substrate 1 is 18:1, and the total thickness is 1.0#.

In this example, the Teflon coating 6 described later is used.
In order to improve the adhesion, the entire surface of the substrate 1 was subjected to roughening electrolytic copper plating 5 using a copper cyanide matte bath. The copper plating 5 is applied to the inside of the lead pin insertion opening 4 to improve the adhesion of the Teflon coating 6 even inside the insertion opening 4. The periphery of the substrate 1 is coated with Teflon coating 6.
#A is not applied, so the copper plating 5 is exposed, but this is for the purpose of rust prevention. The roughness of the copper peg 5 is preferably in the range of 0.5 to 3μ in average surface roughness from the viewpoint of adhesion with Teflon, and the thickness of the copper pew is determined from the viewpoint of preventing corrosion of the end face of the CRC plate 1. At least 2μ or more is required.

After the copper plating 5, insulation treatment is performed by applying a Teflon coating 6 to a portion of the outer peripheral portion of the CIC substrate 1, that is, the heat dissipating portion 7, with a portion remaining. Methods for Teflon coating 6 have been tried, such as fusion tape application, thermal spraying, and molding, but all of these methods allow Teflon to be poured (fill holes) up to the inner surface of the insertion port 4, but there is a problem with the element mounting area 8 and heat dissipation. Since part 7 is not coated, the molding method is most suitable.

Next, a copper-clad Teflon sheet 9 is pasted at a predetermined position on the Teflon-coated substrate 1, and a desired circuit pattern is formed by photoetching the copper sheets 1 to 9 (3S 10). An electrode extraction part 11 is provided on the top, and in order to insert the lead pin 12 from this electrode extraction part 11 into the lead pin insertion hole 4 of the board 1, the lead pin insertion LI4, which has been filled with the Teflon coating, is again drilled with a precision drill or hammered. The insertion hole 1"4 is made into a hole somewhat smaller than the diameter of the lead pin 12, and the lead pin 12 is press-fitted therein by an automatic pin driving device.

For pin press-fitting, in order to make complete electrical contact between the lead pin 12 and the circuit pattern of the copper foil V10, the pin leg is immersed in a molten solder bath and a semi-ITl connection is applied. According to this method, the solder is sucked up between the lead pin 12 and the wall of the insertion opening 4, thereby ensuring electrical connection between the circuit pattern of the upper copper foil thread 10 and the lead pin 12. Eventually, not only the solder layer 13 is formed over the entire pin, but also the solder contact t* layer 15 is formed around the pin head 14.

The PGA substrate is completed as described above, but when mounting, for example, a silicon element 16 on this substrate, the common method of bonding is gold-silicon eutectic bonding on the copper plating 5. Nickel plating on top 17
3μ and about 4μ of gold pegs 18, or gold-silicon eutectic bonding is applied to the cord 16 via gold foil. Then, wire bonding 19 is performed, and the sealing frame (made by Kovar) 2
0 completely sealed with a brazed sushi lid (manufactured by Kovar) 21 and P
Completed GA.

Figure 2 shows the appearance of this PGA. According to this PGA, the outer periphery of the CIC board 1 serves as the heat dissipation section 7;
The reliability of the sealing element can be significantly improved. In addition, in order to match the coefficient of thermal expansion with silicon, the CICLj board 1 is coated with a 0.1 m thick invar on both sides of a 0.8 m thick invar.
clad with oxygen-free copper was used. As already mentioned, the thermal expansion coefficient of the substrate 1 depends on the volume ratio of Invar (which can be set arbitrarily). It must show the relationship between

Example 2 In Example 1, surface roughening nickel plating was applied instead of surface roughening copper plating 5. According to this, the outer circumferential heat dissipating portion 7 of the substrate is not easily discolored due to the induction resistance of nickel, and the -C nickel plating 17 necessary for bonding the silicon element 16 can be omitted.

[Effects of the invention] (1) The PGA prototyped based on the above Example 1 was
IJA Standard IC-121 Thermal Shock Test and [IJA Standard I
Each was tested using the C-121 warm polishing cycle test,
Reliability was compared with a conventional glass epoxy PGA. The test results are shown in Table 2.

According to Table 2, it can be seen that based on this example, the element damage occurrence rate of PGA was very small, and the reliability of the substrate was high. This is related to the adhesion strength of the Teflon coating as well as the coefficient of thermal expansion of the CI i plate.

(2) Conventional Relamic substrates are manufactured by drilling holes in an unsintered sheet (green sheet) and then sintering it, as it is extremely difficult to process holes. Although there is a problem in that the dimensional accuracy of the finished product is not achieved due to shrinkage, the CIC board of this embodiment is very easy to process with the point holes, and is excellent in mass production.

(3) As already mentioned, the substrate of this embodiment has excellent heat dissipation properties, so it is possible to attach highly integrated elements. The temperature increase rate = thermal resistance Rth ('C/W) of the PGA element shown in Fig. 2 is calculated by changing the length a of the heat dissipation part 7 and mounting a silicon element with an output of 20 W. Figure 4 shows the results.As is clear from this, in this example, the thermal resistance of the substrate is very small and the heat dissipation is high by several (8). The device can be highly integrated with the same reliability, and a high applied voltage can be applied, so high speeds can be achieved.

As described above, according to the substrate of the present invention, it is possible to improve the reliability of the PGA, the manufacturing process of the substrate is easy, and because it has excellent heat dissipation properties, it is possible to increase the integration and speed of elements. It has the remarkable effect of being possible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the PGA substrate of the present invention, FIG. 2 is an explanatory diagram of the external appearance of the PGA according to the embodiment, and FIG. 3 is a CI
A characteristic diagram showing the relationship between the Invar volume ratio and the coefficient of thermal expansion in the C substrate. Figure 4 shows the relationship between the length of the heat dissipation part of the PGA shown in Figure 2 and the temperature rise rate of the element part. It is a diagram. 1: CIC board, 2: Copper, 3: Invar, 4: Lead pin insertion port, 5: Copper plating, 6: Teflon coating, 7: Heat dissipation section, 8: Element mounting section, 9: Copper-clad Teflon seam 1~ ．． 10: Copper foil layer, 11: Electrode extraction part, 12: Lead pin, 13: Solder layer, 14: Pin head, 15: Solder connection layer, 16, Silicon element, 17: Nickel plating, 18: Gold plating, 19 : Wire bonding, 20: Sealing frame, 21: M. Agent: Patent Attorney Fujio Sato 6: Thea

Claims (2)

[Claims] (1) The surface of a board made of copper/invar/copper clad material with lead pin insertion holes is rough plated, and a coating of tetrafluoroethylene resin is applied to the rough plated surface except for the heat dissipating parts of the board. A desired circuit pattern is formed using copper foil on the resin coating, an electrode extraction portion is provided on the circuit pattern, and a lead pin is inserted into the insertion hole from the electrode extraction portion. PGA board. (2) The PGA substrate according to claim 1, characterized in that the substrate is roughened by copper plating or nickel plating with a surface average roughness of 0.5 to 3 μm.