JPH05275490A - Mounting method of flip chip - Google Patents

Abstract

PURPOSE:To improve the arrangement precision of flip chips, increase bonding strength to a printed wiping board, enhance electric characteristics, and promote the use efficiency of a printed wiring board. CONSTITUTION:A prepreg sheet 3 wherein aramid short fiber paper is used as reinforcement, and aromatic amine is compounded as adduct harder in impregnated resin is heated at 105 deg.C for 10 minutes, and holes 4 are formed by an ordinary drill method to obtain a board 5 provided with holes. The board 5 is made to abut against the printed wiring board 6 and pressed and heated at 160 deg.C for 30 minutes to be bonded to the board 6. In this case, the surface of the printed wiring board 6 is subjected to inverse sputtering. Holes 6 is filled with silver powder-epoxy resin based conductive paint 9, bumps 2 are made to abut against conductive paint 9. The paint 9 is turned into a B-stage by primary curing at 75 deg.C for 10 minutes, and electric conducting resistance is decreased to inspect the function of a flip chip 1. Acceptable articles are subjected to secondary curing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip mounting method for mounting a flip chip on a printed wiring board for electronic equipment.

[0002]

2. Description of the Related Art A glass cloth / epoxy plate, an alumina magnetic plate, a polyimide film plate, etc. have been typical as a substrate for mounting flip chip type parts.
There is a space between the flip chip body and the substrate, and the characteristics such as thermal conductivity and adhesive area are normal SOP and Q.
It is worse than packages such as FP.

There has been a problem that air is trapped in the resin seal and expands when the temperature rises, causing the bonding bump to float. As a countermeasure, there is an example in which a resin such as an epoxy acrylate, an epoxy / polyimide, or a polyimide, which is UV-curable, is applied to a printed wiring board, selectively developed, and holes for flip chip bump placement are drilled. ..

However, when these UV-curable resins are used for the outer layer of the printed wiring board, the shrinkage factor at the time of curing is large and the directionality is disordered, so that it is difficult to control the position of the holes. However, there was a defect that the position of the bump did not match. The reason for this is that these ultraviolet curable resins receive the reflected light from the printed wiring board having the glass line force. Further, there is a defect that the curing is not uniform due to the influence of the transmittance of ultraviolet rays, and in particular, the bonding property of the boundary on the outer surface of the printed wiring board is directly deteriorated.

Further, the solder heat resistance is low, and the solder is softened by the heating of the reflow soldering, or the cleaning agent such as ME is used.
It has a drawback that it is soluble in K (methyl ethyl ketone), dimethyl formaldehyde and the like. Further, there is a drawback that the expansion and contraction rate due to temperature and humidity is large and the stability in the thickness direction is not as good as in the surface direction.

The electrical characteristics are unstable, and there is a drawback that the degree of migration is large. Also,
10-100 compared to the printed wiring board of the main body in terms of price
It was about twice as expensive. It is possible to use a conductive adhesive for electrical connection of the flip chip legs from the past of die bonding, but the epoxy resin containing the conventional Dicyan diamide curing agent has a migration accelerating property. Since the curing from the A stage to the C stage is rapid and it is difficult to hold it in the B stage, it is inconvenient for the flip chip replacement and the electrical inspection.

[0007]

Conventionally, in order to fix the contact position of the bumps of the flip chip, a photoinitiator is added to acrylic, acrylic and polyimide, or a polyimide resin monomer to form a photosensitive resin on the printed wiring surface. Then, the non-irradiated portion was melted by selective exposure to form a hole having the contact conductor portion of the printed wiring board as the bottom. This method has the following problems.

The positional accuracy of the pattern hole formed of the photosensitive resin is unstable. Migration occurs due to contact with the conductor, and there is acceleration due to the addition of a photoinitiator. The thickness of the photosensitive resin layer needs to exceed the usual coating thickness of 15 μm to 50 to 200 μm, but the degree of curing tends to be insufficient at the boundary with the printed wiring board.

When the photosensitive resin is melted to form the hole, the surface of the contact portion located at the bottom is made into a non-ohmic contact, which hinders electrical connection of the flip chip component. The photo-sensitive resin layer has higher elasticity in the thickness direction with respect to temperature and humidity than that of a printed wiring board, so that the bump bonding portion rises and the bonding portion easily separates.

A known example using silver paint as a bonding assisting means for a bump bonding portion is described in US Pat. S. P. 5,014,1
11 (May 7, 1991), this is
This is to connect the contact between the bump of the flip-chip component and the bottom conductor of the hole, and to prevent excessive expansion and contraction due to humidity after permanent curing of the silver paint, and to prevent silver migration. Not done.

Mounting inspection of the flip chip and replacement after the inspection are almost impossible, and the printed wiring board having the photocurable resin layer formed thereon is discarded together with the flip chip. An object of the present invention is to improve the placement accuracy of a flip chip and the bonding strength to a printed wiring board,
It is an object of the present invention to provide a flip chip mounting method capable of improving electric characteristics and further improving the use efficiency of a printed wiring board.

[0012]

A flip chip mounting method of the present invention is a prepreg sheet in which an aramide short fiber paper is used as a line force and an epoxy resin mixed with an aromatic amine as an adduct curing agent is used as an impregnating resin. After applying the rigid property by heating, form a hole in the flip chip bump mounting position to form a perforated substrate, and perform reverse sputtering on the surface of the printed wiring board to turn the perforated substrate into a printed wiring board. The process of heat-curing from the B stage to the C stage while pressure bonding and adhering the perforated substrate to the printed wiring board, and the temperature direction and humidity in A-stage conductive pane made of epoxy resin that has an expansion / contraction ratio and has an aromatic amine adduct as the resin binder To the holes of the perforated substrate and inserting the bumps of the flip chip into the holes, and the conductive paint is heat-cured on the B stage to lower the contact resistance value to the level of the conductor of the printed wiring board. It is characterized by including a curing step and a secondary curing step of heating and curing the conductive paint on the C stage.

[0013]

According to the constitution of the present invention, a prepreg sheet containing aramide short fiber paper as a line force and an epoxy resin mixed with an aromatic amine as an adduct curing agent as an impregnating resin is heated to impart rigidity. After that, the perforated substrate formed by forming the holes has little dimensional change due to temperature and humidity, the positional accuracy of the holes is stable, and the accuracy of arranging the flip chips can be improved.

Further, by performing reverse sputtering on the surface of the printed wiring board, the bonding strength at the interface between the perforated substrate and the printed wiring board is improved, and the bonding strength between the bumps of the flip chip and the conductors of the printed wiring board is improved. Can be improved. Further, a conductive paint made of an epoxy-based resin that has an expansion / contraction ratio in the thickness direction similar to the expansion / contraction ratio in the thickness direction of a perforated substrate with respect to temperature and humidity and that has an aromatic amine adduct as a resin binder. Is used for the joint between the bump of the flip chip and the conductor of the printed wiring board, the joint strength can be increased and the electrical characteristics such as migration can be improved.

Furthermore, the conductive paint can maintain the B stage in the primary curing step, and in this state, the functional inspection of the flip chip is performed, and the defective chip is replaced with a good chip, and then the secondary curing is performed. By performing the process, the use efficiency of the printed wiring board can be improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process sectional view showing a flip chip mounting method according to an embodiment of the present invention. First, as shown in FIG. 1A, a prepreg sheet 3 having a thickness of about 0.2 mm is prepared, the thickness of which is selected according to the length of the bump (leg) 2 of the semiconductor flip chip 1 of 15 mm × 15 mm size. .. The pitch of the bumps 2 of the flip chip 1 is 125 μm. The prepreg sheet 3 uses aramide short fiber paper having a negative temperature expansion coefficient as a line force (aggregate, fiber), and contains 50% by weight of an aromatic amine as an impregnating resin as an impregnating resin. Cl entering from the outside ^- (chlorine ions)
As a trapping agent, a small amount of zinc oxide powder added epoxy resin (hereinafter referred to as "aromatic epoxy") is used. Then, the B-stage prepreg sheet 3 is obtained by impregnating aramide short fiber paper with 55% by weight of aromatic epoxy. This prepreg sheet 3 has 10
By the first heating at 5 ° C. for 10 minutes, it has the rigid property to withstand the later hole processing.

Next, as shown in FIG. 1 (b), the prepreg sheet 3 is made to have a diameter of about 0.15 mm by an ordinary drilling method.
The holes 4 for receiving the bumps are formed as the perforated substrate 5. Here, the portion where the flip chip is to be mounted is shown as a chip body 1'and legs 2 '. The holes 4 may be formed by punching, laser, or the like. Next, as shown in FIG. 1 (c), a perforated substrate 5 is formed on a printed wiring board 6 having a conductor 7 formed by copper foil or copper plating on the surface of, for example, a polyimide glass or epoxy glass having a thickness of 1.5 mm. Under pressure (10 kg / cm ² ) at 160 ° C. for 30
By second heating for a minute, the perforated substrate 5 is bonded to the printed wiring board 6 as shown in FIG. 1 (d), and the holes 4 become the bottomed holes 8.

When adhering the perforated substrate 5 at the resin curing level of the B stage to the printed wiring board 6,
Reverse sputtering is performed on the conductor 7 and the insulating surface on the surface of the printed wiring board 6 at the resin curing level of the C stage. By this reverse sputtering, during the curing process,
The cured surface of the epoxy resin is cleaned to obtain a microporous surface, and the impregnated resin of the perforated substrate 6 is transferred from the B stage to the C stage.
Enhances adherence when heat curing to stage cure level. The reverse sputtering is performed with a high frequency power of 1 kW for 5 minutes, a vacuum degree before introducing nitrogen gas of 6.0 × 10 ⁻⁷ Torr, and a vacuum degree after introducing nitrogen gas of 4.6 × 10 ⁻ with respect to a size of 25 cm × 25 cm. Perform as ³ Torr. The bonding temperature is
At 170 ° C for 30 minutes, the holding pressure is the same as the second heating, 20
It is kg / mm ² .

Next, as shown in FIG. 1 (d), the conductive paint 9 is filled in the bottomed hole 8 and the bump 2 of the flip chip 1 is brought into contact with the conductive paint 9. At this time, it is physically floating in the conductive paint liquid. The conductive paint 9 is a silver powder-epoxy resin type, and the epoxy resin type is an aroma epoxy type, and the conductive paint 9 is B-staged (semi-melted) by primary curing at 75 ° C. for 10 minutes. State), and the conduction resistance is reduced to 10 to 100 milliohms. In this state, it is possible to measure and connect the functional operation characteristics of the flip chip 1 to the printed wiring board 6 in the mounted state.

When it is judged as a non-defective product, a fixed connection to the printed wiring board 6 is measured, and the furnace is put at 125 ° C. for 10 minutes.
Insert the printed wiring board 6 with the flip chip 1 mounted,
The conductive paint 9 is secondarily cured at the C stage so that the conduction resistance is 10 milliohms or less and up to 1 milliohm. On the other hand, when it is determined that the product is defective, it is easy to remove the flip chip 1, and the flip chip 1 is replaced with a new chip. At this time, add a small amount of conductive paint to
Secondary curing is performed, and when it is determined that the product is non-defective, secondary curing is performed.

As described above, according to this embodiment, the temperature,
Instead of a photosensitive resin layer that has a large expansion and contraction rate due to humidity,
Perforated substrate 5 for drilling at B stage or C stage
As a substrate material that can withstand processing of a conductor by a selective etching method and can be formed with a drill, a punch laser, or the like and has a small dimensional change due to temperature and humidity, The position accuracy of 8) can be obtained.

The perforated substrate 5 is a fiber of polyparaphenylenediphenyl ether terephthalamide containing Na ⁺ of several ppm or less as an aggregate instead of the conventional glass fiber containing a large amount of Na ⁺ (sodium ion). as a reference, impregnating resin, to reduce the dicyandiamide are added a few percent by weight as a conventional epoxy curing agent, used after adduct with aromatic amines in approximately equal amounts, entering further externally Cl - ^(chlorine ions) As a trapping agent for the above, a mixture of a small amount of zinc oxide powder is used as a new compounding resin. This curing temperature depends on the type of the lower printed wiring board 6, but is 150
Set it to ~ 180 ° C to handle it. In addition, when the polyimide resin was used, the pretreatment by reverse sputtering was performed on the polyimide resin, but the curing temperature was 220 ° C., which often exceeded the heat resistance limit of the lower printed wiring board, and the conductor was oxidized to cause the boundary. The adhesiveness of is not good. The conventional Dicyan diamide-cured epoxy resin has a low Tg (glass transition temperature) of 125 ° C. at the maximum, and the surface layer portion is melted or burnt by reverse sputtering or plasma treatment, and the adhesiveness is not improved. The new compounded resin has a maximum Tg of 19
As high as 5 ° C, a surface treatment suitable for adhesion is performed. Therefore, the ionic migration durability can be extended by 1 to 2 digits.

The interlayer adhesion between the perforated substrate 5 and the printed wiring board 6 is 0.5 kg / cm without reverse sputtering when the perforated substrate 5 is an aramide epoxy printed wiring board.
However, reverse sputtering yielded 5 kg / cm. However, in the case of the epoxy-impregnated glass base plate cured with Dicyan diamide as the perforated substrate, all of them are 1/5 to 1
Only a strength of / 10 is obtained, which is hardly practical.

Further, by applying the thermosetting method, uniform hardening of the perforated substrate 5 is realized. The curing time is 10 to 120
The curing temperature of the new compounded resin is lower than 215 to 350 ° C. of the polyimide resin, and the soldering at 215 ° C. is acceptable, and the curing of the boundary between the perforated substrate 5 and the printed wiring board 6 does not occur. Sufficiently solved, the adhesive strength is also dramatically improved.

Further, the electrical connection of the contact portion between the bump 1 of the flip chip 1 and the conductor 7 of the printed wiring board 6 is also good because the introduction of the new compound resin of the perforated substrate 5 causes a slight gas emission. It will be Further, as the perforated substrate 5, a novel material from a conventional photocurable resin to a thermosetting epoxy resin is used. Then, the expansion / contraction rate due to temperature and humidity and the adhesiveness to the printed wiring board are improved.
With respect to ionic impurities, a curing agent for epoxy resin is used, in which the addition amount of conventional dicyandiamide is reduced or eliminated, and about 50% by weight of aromatic amine is compounded in the form of an adduct to form a homogeneous thermosetting product. Tg is also 150-1 from the conventional 110-125 ℃
Increase to 95 ° C. In this example, the temperature is 190 ° C. And, the elasticity in the thickness direction is 30 to
50 ppm / ° C, moisture absorption of 0.4 to 0.5% by weight is improved to 12 to 23 ppm / ° C, moisture absorption of 0.2 to 0.3% by weight. In addition, about adhesiveness, it is 0.4-1.6kg from conventional 0.1-0.3kg / cm
/ Cm improves. In this embodiment, the dimensional change is within 0.1% through the primary heating at 105 ° C. for 10 minutes and the secondary heating at 160 ° C. for 30 minutes, which corresponds sufficiently to the mounting accuracy of a single flip chip. it can. Ordinary Dicyan diamide cured epoxy resin exceeds 3% and 10%
Reach The curing temperature depends on the type of the printed wiring board 6, but is set to 150 to 180 ° C. to correspond.

A known example in which silver paint is used as a bonding assisting means for bump bonding is described in US Pat. S. P. 5,014,
111 (May 7, 1991), which is to connect the bump of the flip-chip component with the release of contact with the bottom conductor of the hole, and has a large expansion and contraction value due to humidity after permanent curing of the silver paint. Too much and no migration measures were taken against silver migration.
On the other hand, according to this example, as a novel thermosetting silver paint for the bump bonding portion, the curing agent of the epoxy resin used as the resin binder is reduced by adding several percent by weight of the conventional dicyandiamide. Abolished and compounded around 50% by weight of aromatic amine in the form of adduct with respect to epoxy resin to maintain more stable B stage and C stage conditions than before, especially from 1 megohm to 100 milliohm as the functional resistance value. The switching change of the intermediate curing conditions 70 to 8
It is realized under the conditions of 5 ° C and 5 to 20 minutes. Further, the amount of ionic impurities is set to 5 ppm or less to eliminate the migration tendency, and Zn (zinc) is added within 1 wt% on the conductor powder side to act as a migration suppression strengthening agent. Then, by applying a PCT of 2 atm and a DC voltage, the conventional time of less than 1 hour can be increased to 100 hours or more.

In addition, in the bonding portion of the bump 2 of the flip chip 1, the conductive coating 9 is injected into the hole 8 to lower the connection resistance thereof to make it conductive and the primary curing, and the secondary curing to obtain the bonding strength. The combined use of and makes it possible to replace the flip chip 1 that has been determined to be defective by measuring the functional electrical characteristics after the primary curing, and in many cases, to reproduce the expensive printed wiring board 6 composed of multiple layers. Enables use.

The printed wiring board 6 may be made by impregnating a cloth or paper made of aramide fiber with aromatic epoxy.

[0029]

According to the flip chip mounting method of the present invention, a prepreg sheet containing aramide short fiber paper as a line force and an epoxy resin as an impregnating resin containing an aromatic amine as an adduct hardening agent is heated. Then, the perforated substrate formed by forming the holes after providing the rigid property has little dimensional change due to temperature and humidity, the positional accuracy of the holes is stable, and the arrangement accuracy of the flip chip can be improved.

Further, by performing reverse sputtering on the surface of the printed wiring board, the bonding strength at the interface between the perforated substrate and the printed wiring board is improved, and the bonding strength between the bumps of the flip chip and the conductors of the printed wiring board is improved. Can be improved. Further, a conductive paint made of an epoxy-based resin that has an expansion / contraction ratio in the thickness direction similar to the expansion / contraction ratio in the thickness direction of a perforated substrate with respect to temperature and humidity and that has an aromatic amine adduct as a resin binder. Is used for the joint between the bump of the flip chip and the conductor of the printed wiring board, the joint strength can be increased and the electrical characteristics such as migration can be improved.

Furthermore, the conductive paint can maintain the B stage in the primary curing step, and in this state, the function test of the flip chip is performed, and the defective chip is replaced with a non-defective chip, and then the secondary cure is performed. By performing the process, the use efficiency of the printed wiring board can be improved.

[Brief description of drawings]

FIG. 1 is a process sectional view showing a method of mounting a flip chip according to an embodiment of the present invention.

[Explanation of symbols]

 1 Flip Chip 2 Bump 3 Prepreg Sheet 4 Hole 5 Perforated Board 6 Printed Wiring Board 7 Conductor 8 Hole 9 Conductive Paint

Claims (1)

[Claims] 1. A flip chip mounting method for mounting a flip chip having a bump structure connecting means on a printed wiring board having a conductor formed on the surface thereof, wherein aramide short fiber paper is used as a line force, and an aromatic amine is used. A step of forming a perforated substrate by forming a hole in the bump mounting position of the flip chip after heating a prepreg sheet containing an epoxy resin impregnated with an epoxy resin mixed as an adduct curing agent to provide rigid property, Performing reverse sputtering on the surface of the printed wiring board,
While pressing the perforated substrate against the printed wiring board, press B
A step of heat-curing from the stage to a C stage to bond the perforated substrate to the printed wiring board; and an expansion and contraction in the thickness direction of the perforated substrate with respect to temperature and humidity. And a step of injecting an A-stage conductive paint made of an epoxy-based resin adducting aromatic amine as a resin binder into the holes of the perforated substrate and inserting the bumps of the flip chips into the holes. And heat-curing the conductive paint on the B stage to lower the contact resistance value to the level of the conductor of the printed wiring board.
A method of mounting a flip chip, comprising: a secondary curing step; and a secondary curing step of thermally curing the conductive paint on a C stage.