JP2774409B2 - Flip chip mounting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Glass cloth / epoxy plate, alumina magnetic plate, polyimide film plate and the like have been typical as substrates for mounting flip chip type components.
A space is formed between the flip chip body and the substrate, and the characteristics such as thermal conductivity and bonding area are normal SOP, Q
Worse than packages such as FP.

[0003] There is a problem that air is trapped in the resin seal and expands when the temperature rises, causing the bonding bumps to float. As a countermeasure, there has been an example in which a resin such as epoxy acrylate, epoxy / polyimide, or polyimide, which has been cured with ultraviolet light, is applied to a printed wiring board, selectively developed, and holes are formed for flip chip bump placement. .

However, when these ultraviolet curable resins are used for the outer layer of a printed wiring board, the position of the holes is difficult to control because the shrinkage during curing is large and the directionality is disordered. However, there was a disadvantage that the position of the bump did not match. The reason for this is that these ultraviolet curable resins receive reflected light from a printed wiring board having glass reinforcement. In addition, there is a disadvantage that the curing is not uniform due to the influence of the transmittance of ultraviolet rays, and this is directly linked to a decrease in the bonding property particularly at the boundary on the outer surface of the printed wiring board.

In addition, the soldering heat resistance is low, and the soldering agent may be softened by heating during reflow soldering, or may be washed with a cleaning agent such as ME.
There is a disadvantage that it dissolves in K (methyl ethyl ketone), dimethyl formaldehyde and the like. In addition, there is a disadvantage that the expansion and contraction ratio due to temperature and humidity is large and the stability in the thickness direction is not as good as in the surface direction.

There is a drawback that the electrical characteristics are unstable, and particularly the degree of migration is large. Also,
10-100 compared to the printed circuit board of the main unit
It was about twice as expensive. The use of a conductive adhesive for the electrical connection of the flip chip legs can also be considered from the results of die bonding, but the epoxy resin containing the conventional Dicyandiamide curing agent has the acceleration of migration, Since the curing from the A stage to the C stage is rapid and it is difficult to hold the B stage, it is inconvenient for flip chip replacement and electrical inspection.

[0007]

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

[0008] The positional accuracy of the pattern holes formed of the photosensitive resin is unstable. Migration occurs due to contact with a conductor, and there is acceleration due to the addition of a photoinitiator. The thickness of the photosensitive resin layer needs to be 50 to 200 μm, exceeding the normal coating thickness of 15 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 non-ohmic, so that the electrical connection of the flip chip component is hindered. The elasticity of the photosensitive resin layer in the thickness direction with respect to the temperature and humidity is higher than that of the printed wiring board, so that the bonding portion of the bump floats and the bonding portion is easily separated.

A known example using silver paint as a joining assisting means for a bump joining portion is disclosed in U.S. Pat. S. P. 5,014,1
11 (May 7, 1991),
This is to connect the detachment of the contact between the bump of the flip chip component and the bottom conductor of the hole, and there is no measure against the excessive expansion or contraction value due to humidity after permanent curing of the silver paint and migration of silver. Not done.

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

[0012]

SUMMARY OF THE INVENTION A method for mounting a flip chip according to the present invention is a prepreg sheet comprising an aramide short fiber paper as a line reinforcement and an epoxy resin containing an aromatic amine as an adduct hardener and an impregnating resin. After heating to impart rigidity, a hole is formed at the flip chip bump mounting position to form a perforated substrate, and reverse sputtering is performed on the surface of the printed wiring board, and the perforated substrate is formed on the printed wiring board. A step of heating and hardening from the B stage to the C stage while pressing and bonding the perforated substrate to the printed wiring board; A-stage conductive pane made of epoxy-based resin with an elasticity ratio and an aromatic amine adduct as a resin binder Is injected into a hole of a perforated substrate, and a bump of a flip chip is inserted into the hole; and a conductive paint is heated and cured on a B stage to lower the contact resistance to the level of the conductor of the printed wiring board. The method includes a curing step and a second curing step of heating and curing the conductive paint to a C stage.

[0013]

According to the structure of the present invention, rigidity is imparted by heating a prepreg sheet using an aramide short fiber paper as a line reinforcement and an epoxy resin impregnated with an epoxy resin blended with an aromatic amine as an adduct curing agent. After that, the perforated substrate formed by perforating the hole has little dimensional change due to temperature and humidity, stabilizes the positional accuracy of the hole, and can improve the placement accuracy of the flip chip.

Further, by performing reverse sputtering on the surface of the printed wiring board, the bonding strength at the boundary between the perforated substrate and the printed wiring board is improved, and the bonding strength between the flip chip bumps and the conductor of the printed wiring board is improved. Is improved. In addition, a conductive paint made of an epoxy-based resin that has the same degree of expansion and contraction in the thickness direction of a perforated substrate with respect to temperature and humidity, and 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, thereby increasing the joining strength and improving the electrical characteristics such as migration.

Further, the conductive paint can maintain the B stage in the primary curing step. In this state, the function inspection of the flip chip is performed, 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 increased.

[0016]

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 one embodiment of the present invention. First, as shown in FIG. 1A, a prepreg sheet 3 having a thickness of about 0.2 mm, which is selected according to the length of a bump (leg) 2 of a semiconductor flip chip 1 having a size of 15 mm × 15 mm. . The pitch of the bumps 2 of the flip chip 1 is 125 μm. The prepreg sheet 3 uses an aramid short fiber paper having a negative coefficient of thermal expansion as a line reinforcement (aggregate, fiber), and blends 50% by weight of an aromatic amine as an impregnating resin as an adduct hardener. Cl entering from the outside ^- (chlorine ions)
As a trapping agent, an epoxy resin to which a trace amount of zinc oxide powder is added (hereinafter referred to as "aroma epoxy") is used. Then, a B-stage prepreg sheet 3 impregnated with aramid staple fiber paper with 55% by weight of aroma epoxy is used. This prepreg sheet 3 has 10
By primary heating at 5 ° C. for 10 minutes, it has rigidity to withstand subsequent 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 a usual drilling method.
A hole 4 for receiving a bump is formed to form a perforated substrate 5. Here, the portions where the flip chip is to be mounted are shown as a chip body 1 'and a leg 2'. The holes 4 may be formed by a punch, a laser, or the like. Next, as shown in FIG. 1 (c), a printed wiring board 6 having a conductor 7 formed by copper foil or copper plating on a surface of, for example, 1.5 mm thick polyimide glass or epoxy glass is provided with a perforated substrate 5. At 160 ° C., 30 ° C. under pressure (10 kg / cm ² ).
By the second heating, the perforated substrate 5 is bonded to the printed wiring board 6 as shown in FIG. 1D, and the hole 4 becomes a hole 8 with a bottom.

When bonding 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
Enhance adhesion when heating and curing to the stage curing level. Reverse sputtering, to the size of 25 cm × 25 cm, RF power 1 kW, 5 minutes, nitrogen gas inlet before vacuum 6.0 × 10 ^-7 Torr, a nitrogen gas inlet after the vacuum degree 4.6 × 10 ^- Perform as ³ Torr. The bonding temperature is
At 170 ° C. for 30 minutes, the holding pressure is the same as that of the second heating: 20
kg / mm ² .

Next, as shown in FIG. 1D, 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 in a state of floating in the conductive paint liquid. Using a silver powder-epoxy resin-based material as the conductive paint 9 and an aroma epoxy-based epoxy resin, 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 mOhm. In this state, it is possible to measure and connect the functional operation characteristics of the flip chip 1 mounted on the printed wiring board 6.

If it is determined that the product is non-defective, a fixed connection to the printed wiring board 6 is performed in a furnace at 125 ° C. for 10 minutes.
Insert the printed wiring board 6 on which the flip chip 1 is mounted,
The conductive paint 9 is secondarily cured in the C stage to reduce the conduction resistance from 10 mOhm to 1 mOhm. On the other hand, if it is determined that the product is defective, it is easy to remove the flip chip 1 and replace it with a new chip. At this time, a small amount of conductive paint is added to make the first
The secondary curing is performed, and if it is determined to be a non-defective product, the secondary curing is performed.

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

The perforated substrate 5 is made of a fiber made of polyparaphenylenediphenyl ether terephthalamide in which Na ⁺ is several ppm or less, instead of the conventional glass fiber containing a large amount of Na ⁺ (sodium ions) as an aggregate. Using a resin obtained by reducing the amount of dicyandiamide added as a conventional epoxy curing agent by several percent by weight as an impregnating resin and adducting an aromatic amine in an approximately equal amount, and further entering Cl ⁻ (chlorine ion) from the outside Of a small amount of zinc oxide powder is used as a novel compounding resin. Although this curing temperature depends on the type of the lower printed wiring board 6,
It corresponds by setting to ~ 180 ° C. 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, the conductor was oxidized, and the boundary Also has poor adhesion. Conventional epoxy resin cured with dicyandiamide has a low Tg (glass transition temperature) of 125 ° C. at the maximum, and the surface layer is melted or burnt by reverse sputtering or plasma treatment, and the adhesion is not improved. New compound resin has Tg of up to 19
As high as 5 ° C., surface treatment suitable for bonding is performed. Therefore, the ionic migration durability can be extended by one to two 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 aramid epoxy printed wiring board.
However, 5 kg / cm was obtained by reverse sputtering. However, in the case of an epoxy-impregnated glass base plate cured with dicyandiamide as a perforated substrate, all are 1/5 to 1
/ 10 strength is hardly obtained.

Further, uniform hardening of the perforated substrate 5 is realized by applying the thermosetting method. Curing time is 10-120
The curing temperature of the novel compounded resin is lower than the polyimide resin of 215 to 350 ° C., 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 is not completed. Sufficient elimination is achieved, and the adhesive strength is dramatically improved.

Also, the electrical connection at the contact portion between the bump 1 of the flip chip 1 and the conductor 7 of the printed wiring board 6 is excellent because the introduction of a new compound resin of the perforated substrate 5 causes a small amount of gas release. It becomes something. Further, as the perforated substrate 5, a new material of a thermosetting epoxy resin from a conventional photocuring resin is used. Then, the expansion and contraction rate due to temperature and humidity and the adhesiveness to the printed wiring board are improved.
Regarding ionic impurities, the curing agent of the epoxy resin is reduced or abolished by several percent by weight of the conventional dicyandiamide, and about 50 percent by weight of the aromatic amine is blended in the form of an adduct to obtain a homogeneous thermosetting product. The Tg is also increased from the conventional 110 to 125 ° C. to 150 to 1
Increase to 95 ° C. The temperature is set to 190 ° C. for this embodiment. And the elasticity in the thickness direction is 30 to
50 ppm / ° C, 0.4-0.5 weight percent moisture absorption is improved to 12-23 ppm / ° C, 0.2-0.3 weight percent moisture absorption. In addition, about 0.1-0.3kg / cm of conventional about 0.1-0.3kg / cm, it is 0.4-1.6kg.
/ Cm. 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 sufficiently corresponds to the mounting accuracy of a single flip chip. it can. More than 3% for ordinary dicyandiamide-cured epoxy resin, 10%
Reach The curing temperature depends on the type of the printed wiring board 6, but is set at 150 to 180 ° C. to respond.

It is to be noted that a known example using silver paint as a joining assisting means for a bump joining portion is disclosed in U.S. Pat. S. P. 5,014,
111 (May 7, 1991), which is to connect the detachment of the contact between the bump of the flip-chip component and the bottom conductor of the hole, and the expansion and contraction value of the silver paint due to humidity after permanent curing is large. No countermeasures were taken against excessive migration and silver migration.
In contrast, according to this embodiment, as a novel thermosetting silver paint for the bump joint, the amount of the epoxy resin curing agent used as the resin binder is reduced by several percent by weight of conventional dicyandiamide or Abolished and blended around 50% by weight of aromatic amine with epoxy resin in the form of adduct to maintain more stable B-stage and C-stage than before, especially from 1 megohm to 100 milliohm as functional resistance Of the intermediate curing conditions 70 to 8
It is realized at 5 ° C. for 5 to 20 minutes. Further, the amount of the ionic impurities is set to 5 ppm or less, the tendency of migration is eliminated, and Zn (zinc) of 1% by weight or less is added on the conductor powder side to act as a migration suppressing and strengthening agent. By applying a PCT pressure of 2 atmospheres and applying a DC voltage, it is possible to reduce the conventional time within one hour to 100 hours or more.

Also, conductive paint 9 is injected into the holes 8 at the joints of the bumps 2 of the flip chip 1 to lower the connection resistance and make a conductive state, and a second hardening for obtaining the bonding strength is performed. In combination with the above, the functional electrical characteristics are measured after the primary curing, and the flip chip 1 determined to be defective can be replaced. In many cases, the expensive printed wiring board 6 composed of multiple layers is reproduced. Enable use.

A material obtained by impregnating cloth or paper made of aramid fiber with aroma epoxy may be used for the printed wiring board 6.

[0029]

According to the flip chip mounting method of the present invention, a prepreg sheet made of an aramide short fiber paper as a line reinforcement and an epoxy resin impregnated with an epoxy resin containing an aromatic amine as an adduct curing agent is heated. After the rigidity is imparted, the perforated substrate formed by perforating the hole has a small dimensional change due to temperature and humidity, stabilizes the position accuracy of the hole, and can improve the placement accuracy of the flip chip.

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 flip chip bumps and the conductor of the printed wiring board is improved. Is improved. In addition, a conductive paint made of an epoxy-based resin that has the same degree of expansion and contraction in the thickness direction of a perforated substrate with respect to temperature and humidity, and 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, thereby increasing the joining strength and improving the electrical characteristics such as migration.

Further, the conductive paint can maintain the B stage in the first curing step. In this state, the function of the flip chip is inspected, the defective chip is replaced with a good chip, and then the second curing is performed. By performing the process, the use efficiency of the printed wiring board can be increased.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION 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)

(57) [Claims] 1. A method of mounting a flip chip having a connection structure having a bump structure on a printed wiring board having a conductor formed on a surface thereof, the method comprising the steps of: After heating a prepreg sheet containing an epoxy resin impregnated resin blended as an adduct curing agent to impart rigidity, forming a perforated substrate by opening holes at the bump mounting positions of the flip chip, Perform reverse sputtering on the surface of the printed wiring board,
While pressing the perforated board against the printed wiring board,
Bonding the perforated substrate to the printed wiring board by heating and curing from a stage to a C stage; and expanding and contracting in a thickness direction of the thickness direction of the perforated substrate with respect to temperature and humidity. A step of injecting an A-stage conductive paint made of an epoxy-based resin having an aromatic amine as a resin binder into the hole of the perforated substrate, and inserting the flip chip bump into the hole. A first step of heating and curing the conductive paint on a B stage to lower the contact resistance value to the level of the conductor of the printed wiring board;
A method for mounting a flip chip, comprising: a next curing step; and a second curing step of heating and curing the conductive paint on a C stage.