JP3045697U - Package substrate for chip mounting - Google Patents

Abstract

(57) [Summary] [Problem] To provide a package substrate which can easily and reliably perform rework, and is excellent in heat dissipation from a chip and heat resistance history. In a package substrate provided with a protruding electrode that is melted and connected to an electrode on a motherboard side, the protruding electrode includes:
100-600 μm that does not substantially heat melt during fusion splicing
, And a low-melting-point metal layer applied so as to cover at least the distal end of the electrode main body.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a package board for mounting a chip, and more particularly, to a so-called BGA (Ball Grid Array) type package board that is fused to an electrode on the board side at the time of mounting on a motherboard at a protruding electrode.

[0002]

[Prior art]

 Due to the high integration of semiconductor devices, the package mounting semiconductors is rapidly becoming multi-electrode. Along with this, the form of the package has been changed from QFP to TCP and further to BGA, and the package has been reduced in size despite the increase in the number of electrodes. Since BGA has more terminals than other methods, BGA is widely used as the latest technology among them.

[0003] The mounting method of the BGA package on the motherboard is to print reflow solder on predetermined connection points of the motherboard, fix solder balls on the connection points of the BGA package, accurately align them, and then reflow the furnace. The solder is melted and connected. Since the solder balls lose their shape due to melting, the gap between the package substrate and the motherboard becomes very narrow, almost equal to a gap.

[0004]

[Problems to be solved by the invention]

 Semiconductor devices are easy to cause troubles due to their complicated circuits, and there are many problems that cannot be detected by inspection before mounting on the package substrate and are first detected after mounting on the motherboard. In addition, it is often the case that trouble is caused by the improper use of the product.

[0005] The best solution in the event of a trouble is to replace the defective package. However, only the package substrate such as the surface-mounted BGA is removed, and another package substrate is mounted again ( Rework) is in a difficult state.

That is, in order to remove the package substrate, it is necessary to re-melt and remove the solder connecting the package substrate and the motherboard again. At this time, if the heat at the time of re-melting reaches other elements, the solder connecting the elements is melted, which increases the probability of occurrence of abnormal connection of the elements after the replacement of the package substrate. It is not preferable from the viewpoint of reuse of the user board.

In order to mount a new package substrate on the trace of the removed package substrate and obtain reliable connection, reflow solder must be printed again at the connection points of the motherboard. However, it is difficult to print reflow solder accurately at the connection points due to the influence of other elements, and it is difficult to re-mount the package substrate to the motherboard.

In addition, the amount of heat generated increases as the degree of integration of the chip increases, and if heat radiation is not ensured, runaway due to heat may be caused. As a current heat dissipation measure, a cooler etc. is installed for those with a large amount of heat generation for forced cooling, but sufficient heat dissipation measures are not taken for inexpensive chips.

[0009] Furthermore, due to heat history, cracks occur in a part of the solder used for connection between the motherboard and the package substrate, thereby causing poor conductivity, and the need for reworking has come up frequently. .

[0010]

[Means for Solving the Problems]

 In view of the above problems, the present inventors have made various studies and provided an electrode body having a predetermined protruding height that does not substantially melt at the time of fusion connection, instead of a solder ball in a BGA, and provided at the tip of the electrode body. Low melting point metal layers such as tin and bismuth; low melting point alloy layers such as tin-lead alloy and tin-bismuth alloy; and low melting point alloy layers containing silver in these low melting point metals or low melting point alloys; By providing a conductive paste layer containing these alloys and melting at a low melting point, the amount of reflow solder required for the motherboard is not significantly reduced or required, and mounting / removing is possible regardless of the fusion connection method. In addition, a sufficient gap can be secured between the package substrate and the motherboard based on the protruding height of the electrode body, and the present invention is excellent in heat dissipation and heat history. Which has led to may provide a package substrate.

[0011]

[Embodiment of the invention]

 An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 schematically shows the chip mounting surface side of the package substrate A of the present invention, and FIG. 2 schematically shows the protruding electrode forming surface side. The basic configuration is substantially the same as that of the conventional product.

FIG. 3 is a longitudinal sectional view schematically showing, in an enlarged scale, the through hole in FIGS. 1 and 2 and the structure in the vicinity of the through hole. 1 is a main body of the package substrate of the present invention, and 2 is an electrode main body. Numeral 3 indicates a low melting point metal layer, numeral 4 indicates a through hole, and numeral 5 indicates a front and back conductor pattern connected through the through hole 4, respectively.

In the present invention, the base material 1a of the main body 1 of the package substrate can be made of a material used for printed wiring. That is, laminated sheets such as glass epoxy resin laminated sheets, fluororesin sheets represented by Teflon, polyimide resin laminated sheets, engineering resin sheets such as BT resin, PP, PES, PET, PEEK, and composites of these plastics and inorganic substances And various ceramic plates such as oxide ceramic plates such as alumina, nitride ceramic plates such as aluminum nitride, carbide ceramics such as silicon carbide, amorphous insulators such as glass, etc. A metal laminate in which copper foil or the like is laminated as a metal layer on an insulator can be used.

A required number of through holes 4a are formed in the substrate 1a, and electroless copper plating, electroplating, lamination of a plating resist layer, pattern exposure to the resist layer, development, secondary electrolytic copper plating, By forming the pattern 5 through the steps of plating the etching resist metal layer, stripping the plating resist layer, etching, and stripping the etching resist metal layer, the main body 1 which is the basis of the package substrate of the present invention is obtained. The method of forming the pattern 5 on the main body 1 of the package substrate may be performed by other known methods.

Next, with respect to the main body 1, the electrode main body 2, which is the most characteristic feature of the present invention, is formed so as to be aligned with the electrode on the motherboard (not shown). In forming the electrode main body 2, first, as shown in FIG. 4A, a plating resist layer 6 is formed on the surface of the main body 1 on the side where the protruding electrodes are formed. The plating resist layer 6 has a function as a plating resist in a normal printed wiring board manufacturing process such as a dry film and a liquid resist, and hardly causes light scattering in the resist at the time of exposure. The thickness is not particularly limited as long as the thickness is 1.01 to 1.05 times the protruding height and a hole corresponding to the diameter of the electrode body 2 can be obtained by development. The thickness of the resist layer 6 is set to be 1.01 to 1.05 times the required projection height of the electrode main body 2 because of the pattern width and the pattern thickness of the pattern 5 of the main body 1 described above. The purpose of this is to make the current distribution in the electrode body forming portion at the part and the work edge part uniform, and also to make the current distribution in the resist hole uniform and suppress the growth near the interface with the resist layer 6.

In order to obtain the above effect, the amount of increase in the thickness of the resist layer 6 decreases as the required protrusion height of the electrode body 2 increases, and the required protrusion height of the electrode body 2 decreases. The ratio may be increased, and specifically, it may be appropriately selected and determined within the above range according to various conditions such as plating conditions, a required protrusion height of the electrode body, and a diameter of the electrode body 2.

After laminating the resist layer 6 on the main body 1, as shown in FIG. 4B, a pattern matching the electrode pattern on the package side is formed to form a hole 7 for forming an electrode main body. Exposure and development are performed so that

The light wavelength used for the exposure is a wavelength corresponding to the resist layer 6 to be used, and light that is hardly scattered in the resist layer 6 since the resist layer 6 is relatively thick may be used. Light and the like can be exemplified.

The development is generally performed with an aqueous solution of potassium carbonate or an aqueous solution of sodium carbonate. If the resist layer 6 to be used corresponds to these solutions, these solutions may be used. If a solvent, etc.) is specified, the specified substance may be used.

The development of the resist layer 6 is important, and if there is a residue of the resist layer 6 in the electrode forming portion, the portion is not plated, so that the electrode main body 2 cannot be formed. For this reason, it is preferable that the development and shower washing are repeated, and the developing solution or the resist remaining in the hole 7 is surely removed by shower washing instead of performing the development at once.

After the holes 7 for forming the electrode main body are provided in the resist layer 6, the plating step for forming the electrode main body 2 is started through the steps of degreasing and pickling.

As the plating solution, a plating solution obtained by adding a commercially available additive (for example, MM-10 manufactured by Daiwa Special Co., Ltd., Copperglyme manufactured by Nippon Lee Ronal Co., Ltd.) to a plating solution used for pattern copper plating (ie, sulfuric acid) Copper: a plating solution exemplified by 70 to 90 g / l, copper sulfate: 170 to 210 g / l), a plating solution for electroforming (that is, copper sulfate: 200 to 250 g / l, sulfuric acid: 10 to 50 g / l) And an additive (a plating solution exemplified by phenolsulfonic acid, molasses, dextrin, casein, glue, acetyl cyanamide, thiourea, etc.), or a plating solution for printed circuit boards.

The plating can be applied by combining different plating methods. That is, electroless plating → electroplating, electroless plating → electroforming plating, electroless plating → electroplating → electroforming plating, electroless plating → electroforming plating → electroplating, electroplating → electroless plating, electroplating → Electroforming plating, electroplating → electroless plating → electroforming plating, electroplating → electroforming plating → electroless plating, electroforming plating → electroless plating → electroplating, electroforming plating → electroplating → electroless plating, Electroplating or electroforming plating (compression stress type) → electroplating or electroforming plating (tensile stress type), electroplating or electroforming plating (tensile stress type) → electroplating or electroforming plating (compression stress type), etc. It is.

The conditions for electrodeposition may be appropriately selected depending on various conditions such as the composition of the plating solution and the plating thickness. In the case of electroplating, the current density is preferably 4 to 6 A / dm 2, and the plating temperature is in the range of 20 to 50 ° C. Is preferred. In the case of using electroless copper plating, it is only necessary to follow the manufacturer's instructions for the chemical used.

In order to sufficiently distribute the plating pretreatment solution such as a degreasing solution and the plating solution to the inside of the hole 7 for forming the electrode body, no bubbles should be introduced into the hole 7, and the solution exchange in the hole 7 should be promptly performed. Must be done. As a method for this, the ultrasonic wave, the shock method, the oscillating method, and the jetting method of the treatment liquid which have already been proposed may be appropriately combined. The current density may be determined within the above range in consideration of the liquid exchange speed in the hole 7 due to the above.

FIG. 4C shows a state after the electrode main body 2 is formed by applying the plating means. After the electrode main body 2 is formed, the resist layer 7 is peeled off to obtain the state shown in FIG. As shown, the main body 1 having the electrode main body 2 is obtained. The peeling and removal of the resist layer 6 may be performed with a chemical such as an aqueous NaOH solution or an organic solvent designated by the resist, and is not particularly limited.

The obtained electrode body 2 can be subjected to electroless nickel plating, electroless gold plating or gold plating by a known method.

It is necessary that the electrode body 2 does not substantially melt when the low-melting metal layer 3 is thermally melted, and the above-mentioned copper plating is generally used. In addition, plating of a copper alloy, nickel, a nickel alloy, or the like is performed. It may be.

The electrode body 2 does not substantially melt at the time of fusion splicing, so that an interval of a vertical width approximately corresponding to the protruding height can be formed between the electrode main body 2 and the motherboard. The protruding height of the electrode body 2 needs to be at least 100 μm, so that a space of at least 50 μm can be formed between the electrode body 2 and the motherboard. The upper limit of the protruding height can be limited to a maximum of about 600 μm due to limitations in plating technology and processing cost.

By attaching the low melting point metal layer 3 on the electrode body 2 in the state shown in FIG. 4D, the package substrate A of the present invention is obtained as shown in FIG.

The low-melting point metal layer 3 is used for connecting to an electrode on the board side by heat melting when mounted on a motherboard, and is made of a low-melting point metal.

Examples of the metals (including alloys) that can be used here include tin and bismuth, which are low-melting metals, and the alloy has a eutectic point of 260 ° C. or less, and at least one of these metals. Alloys containing at least one of them are suitable. Such alloys include tin-lead alloy (solder), tin-bismuth alloy, tin-silver alloy, tin-aluminum alloy, tin-cadmium alloy, tin-indium alloy, tin-zinc alloy, bismuth-cadmium. Alloys, bismuth-lead alloys, bismuth-zinc alloys, and the like.

As one of the methods for applying the low melting point metal layer 3 to the electrode body 2, a plating method can be exemplified, and an electroplating method, an electroless plating method, and a hot-dip plating method are used for the characteristics of metals and alloys. What is necessary is just to select and apply in consideration of a process etc.

As another deposition method, a conductive paste containing the above-mentioned metal or alloy and having a characteristic of melting at 260 ° C. or less and having excellent conductivity is used, for example, by applying printing means. The method can be exemplified.

The amount of the low-melting metal and the conductive paste to be applied is determined by the relationship with the motherboard on which the substrate of the present invention is mounted, that is, the size of the electrode body 2, the line width, the line interval, the warpage of the motherboard, and the like. Although it cannot be determined unambiguously, the results of various studies conducted by the present inventors show that the electrode body 2 can be favorably formed by depositing the low melting point metal layer 3 having a thickness of 20 to 50 μm. Results have been obtained. The optimum amount of the low melting point metal and the like is affected by various factors as described above, and is not necessarily limited to this range. However, if low-melting-point metal is excessively adhered, problems such as short-circuiting are likely to occur during mounting on the motherboard.If insufficient, insufficient connection with the electrodes will result in no electrical connection or Even if this is done, long-term reliability will be lacking, so the deposition rate should be set to an appropriate value.

Hereinafter, a production example and a performance test result of the product of the present invention will be described.

[0038]

[Manufacturing Example 1] A circuit pattern was formed on a 300 mm x 400 mm glass-epoxy copper-clad laminate obtained by laminating 18 µm copper foils by an ordinary method for producing a printed board. That is, a copper-clad laminate is drilled, a dry film is laminated after electroless copper plating, a circuit pattern is baked on the dry film by ultraviolet rays, development with alkali, electrolytic copper plating, solder plating, dry film peeling, copper etching and solder etching. A 200 μm-thick dry film (prototype) was laminated on a substrate on which a predetermined circuit pattern was formed through the above steps by a vacuum laminator, and exposure was performed using an ultraviolet parallel exposure machine in the same manner as when manufacturing a printed circuit board. . For development, a 1% Na2CO3 aqueous solution is used as a developing solution, and a belt conveyor type developing machine is used. The developing solution is sufficiently spread to the inside of the hole by spraying, and then, washing with water is also performed by spraying, and the developing solution and resist remaining in the hole are sprayed. Was removed. This operation was repeated five times, and the hole for forming the electrode body was removed from the hole. After confirming that 1% of the resist did not remain by loupe observation, the steps of degreasing, pickling and electroplating were performed. Degreasing was performed using a commercially available acidic degreasing solution, and pickling was performed using 10% sulfuric acid under known processing conditions. Next, for plating, the plating solution is copper sulfate 80 g / l, sulfuric acid 190 g / l, brightener (MM-10, Daiwa Special Co., Ltd.) 6. A bath composition of 3 ml / l was used. Plating conditions were plating at a current density of 4 A / dm 2 and a bath temperature of 25 ° C. for 3.7 hours to obtain an electrode body 2 having a plating thickness of 195 μm.

After the plating, the resist was stripped with a 1% NaOH aqueous solution, and then a low-melting metal layer 3 was applied on the tip of the electrode body 2 to an area of about 50 μm by an average of 20 μm by applying a hot-dip plating means to obtain the present invention. . This product was mounted on a motherboard on which a reflow solder was printed in advance with no chip mounted, but no particular problems occurred during mounting. In addition, the mounted package substrate was heated by hot air to melt the solder, the package substrate was removed, and mounting was performed while the solder was melted by hot air at the location where the new package substrate was removed.

[0040]

[Performance Test 1] The heat radiation performance of the conventional product and the present product was examined. Here, the conventional product refers to the package substrate having a shape in which the package substrate has solder balls and is integrated by heat melting together with the reflow solder printed on the motherboard. Refers to a package substrate obtained by the method. Heating elements were mounted on these package substrates, sealed with resin, created a state similar to the heat generated by chip mounting, and the amount of current applied to the heating elements to maintain a constant temperature was measured. The gap between the package substrate and the motherboard was almost zero in the conventional product, and was 150 μm on average in the product of the present invention. The reason that the distance between the mother boat and the electrode body 2 is smaller than the projection height of 195 μm is that the solder resist (not shown) is coated on the mother board and the present invention. This is because the gap is reduced by an amount corresponding to about 20 to 25 μm). The temperature was measured with a contact-type surface thermometer, and when one of the temperatures decreased, the amount of current flowing through the decreased heating element was adjusted so that the surface temperatures of both decreased. Table 1 shows a comparison in which each of the ten samples was performed and the amount of current passed through the conventional product was set to 100. Table 1 Set temperature Conventional product Gap 50 μm Gap 100 μm Gap 200 μm 40 ° C. 100 103 110 115 50 ° C. 100 105 112 120 60 ° C. 100 106 116 138 As shown in Table 1, in order to keep the surface temperature constant in the present invention, More current flow was required. This is due to the fact that the product of the present invention has a better heat dissipation effect than the conventional product and the surface temperature has dropped.

[0041]

[Performance Test 2] The resin of the present invention created based on Production Example 1 and the conventional product used in Performance Test 1 were put on the chip mounting portion with resin, and the conditions were almost the same as when the chip was mounted. 100 cycles of a temperature cycle test with a holding time of 30 seconds at each temperature of + 250 ° C / room temperature under the condition of + 250 ° C / room temperature, and the situation between the motherboard and the product and between the motherboard and the conventional product. Investigated the situation. The inspection method was as follows. The temperature cycle test product was removed except for the chip mounting substrate, and the chip mounting portion was fixed with resin, and then exposed by polishing to a state where the protruding electrodes and solder balls could be observed, and the respective conditions were examined. Table 2 shows the results. Table 2 Present invention product Conventional product Situation before test No abnormalities were observed No abnormalities were observed No post-test conditions No abnormalities were observed Cracks were observed Cracks were observed in some of the solder balls by observing the status of the conventional products after the tests Therefore, the resin on the chip mounting part was removed, the bonding pads were exposed, and a continuity test with the motherboard was performed. As a result, stable conduction was confirmed in all products of the present invention, but unstable conduction was partially observed in the conventional product.

[0042]

[Effects of the Invention] As described above, the package substrate according to the present invention is easy and reliable to rework, and has not only excellent heat dissipation from the heat generated from the chip but also a strong heat history. doing.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing an embodiment of the present invention.

FIG. 2 is a bottom view of the same.

FIG. 3 is a partially enlarged longitudinal sectional view schematically showing a state of formation of a protruding electrode.

FIG. 4 is a process diagram schematically showing a process of forming an electrode body.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Body portion of package substrate 2 Electrode body 3 Low melting point metal layer 4 Through hole 5 Conductor pattern 6 Plating resist layer 7 Hole

Claims (6)

[Utility model registration claims] 1. A package substrate having a protruding electrode fused to an electrode on a motherboard side, wherein the protruding electrode is:
100-600 μm that does not substantially heat melt during fusion splicing
A chip mounting package substrate, comprising: an electrode body having a protruding length. 2. The package substrate according to claim 1, wherein a low melting point metal layer is applied so as to cover at least a tip portion of the electrode body. 3. The package substrate according to claim 1, wherein the electrode body is formed by applying at least one of an electroplating method, an electroless plating method and an electroforming plating method. 4. A method for printing a conductive paste in which the low melting point metal layer is formed by applying at least one of an electroplating method, an electroless plating method and a hot-dip plating method, or a conductive paste containing a low melting point metal as a main component. The package substrate according to claim 2, wherein the package substrate is attached to the electrode body by applying the following. 5. The package substrate according to claim 4, wherein the low melting point metal is at least one of tin and bismuth, or an alloy of these metals and a metal having a eutectic point of 260 ° C. or less. . 6. When mounted on a motherboard, at least 50 based on the protruding height of the electrode body between itself and the motherboard.
The package substrate according to any one of claims 1 to 5, wherein an interval of μm can be formed.