RU2648311C2 - Method of insulation for mounting of flip chips - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: use: for assembling three-dimensional integrated circuits (ICs) of 3D BIS. Invention consists in the fact that the insulation method for flip chips mounting includes an assembly, on which crystals with contact columns and substrates with metallization on contact areas from solder of a given thickness arrive, an adhesive tape is placed between the crystal and the substrate, having holes, the pattern of which is a mirror image of the arrangement of the contact columns on the crystal, when assembled, the contact posts of the crystal through the holes in the tape are combined with the solder of the contact pads on the substrate, then the brazing is carried out in a vacuum, when heated to the soldering temperature and the pressure on the crystal, the solder is melted, thus, the soldering of the entire surface of the contact columns of the crystal takes place, as a result of which the gap between the contact posts and the holes in the adhesive tape is filled, and since the thickness of the tape is commensurable with the distance between the crystal and the substrate, then under pressure of the crystal and at the soldering temperature, a tight banding of the tape occurs with the surfaces of the crystal and the substrate, which eliminates not only the spreading of solder on the surfaces of the crystal and the substrate and a short circuit between the contacts of the device, but also the formation of pores on the border of the tape with the soldered surfaces of the crystal and substrate.

EFFECT: technical result: providing the possibility of increasing the heat dissipation from the crystal to the substrate.

4 cl, 2 dwg

Description

The invention relates to the field of microelectronics, in particular the assembly of three-dimensional integrated circuits (IC) 3D LSI. One of the main operations in the production of 3D BIS ICs is the attachment of crystals with volumetric leads to the bases of cases or substrates by the flip-chip method. The inverted crystal method is based on contact poles located on metallized contact pads of crystals.

The crystals are mounted on the base of the housings or substrates with the planar side. At the same time, the drawing of their contact pads is a mirror image of the location of the terminals (flip-chip technology).

The reliability of 3D IC LSIs manufactured using the flip-chip technology, largely depends on the material deposited under the crystal between its front surface and the substrate. At the last stage of the assembly of semiconductor products, the space between the crystal is filled with "filling" - a non-conductive adhesive that connects the entire surface of the crystal to the substrate. "Filling" performs the function of protecting contact columns from moisture and other components of the atmosphere, provides additional mechanical strength of the connection "crystal - substrate".

There is a known [1] method of mounting a crystal by the flip-chip method, in which protrusions (contact posts) are formed on the crystal from gold coated with In-Sn solder. Installation is carried out by heating to a temperature not exceeding the melting point of the solder. Then, thermoplastic is introduced (“filled”) into the gap between the crystal and the substrate and heat treatment is performed a second time to ensure reliable mechanical connection of the crystal with the substrate.

The main disadvantage of this method is the double heating operation, which increases the cost of manufactured devices. In addition, with this installation method, voids are always present, especially at the border with the contact posts. It is known that the maximum area of the connection of the crystal with the substrate will be in the event that its entire surface is moistened with a thermoplastic. In fact, it is not possible to completely fill the space between the crystal and the substrate with thermoplastic. This is prevented by air being sealed in a confined space in irregularities (protrusions). The air pressure is balanced by external pressure, which prevents the penetration of the thermoplastic deep into irregularities.

The presence of voids reduces the heat removal from the crystal to the substrate of the assembled product during operation.

In order to reduce (eliminate) the pores in the "crystal - substrate" gap, it is advisable to solder in a vacuum.

It is recommended [2] to improve the reliability of soldered connections of components with ball terminals (BGA, CSP) using Underfilling technology. The essence of this technology is to fill the space under the crystal between the ball contacts with a polymer material and then cure it. It is argued that due to the selected coefficients of linear expansion of materials, polymer filling (Underfilling) significantly reduces the thermomechanical load on the soldered joint, and also seals the space under the crystal.

The main disadvantage of this technology is the presence of voids in the space under the crystal between the ball contacts, which reduces the heat removal from the crystal to the substrate.

The problem to which the claimed solution is directed is to reduce the cost of manufactured products and increase the heat removal from the crystal to the substrate. This task is achieved by the fact that an adhesive tape having holes is placed between the crystal and the substrate, the pattern of which is a mirror image of the location of the contact columns on the crystal, during assembly, the contact columns of the crystal through holes in the tape are combined with the solder pads on the substrate, then soldering in vacuum , when heated to soldering temperature and pressure on the crystal, the solder melts, and the entire surface of the contact columns of the crystal is wetted by solder, as a result of which oiskhodit filling of the gap between the bumps and holes in the adhesive tape, and since the thickness of the tape is commensurate with the distance between the crystal and the substrate, then under the pressure of the crystal and at the soldering temperature there is a tight connection of the tape with the surfaces of the crystal and the substrate, which excludes not only the spreading of solder on the surfaces of the crystal and the substrate and short circuit between the contacts of the device, but also the formation of pores on the border of the tape with soldered surfaces of the crystal and the substrate.

Comparison of the proposed method of isolation during the installation of inverted crystals with other methods [1, 2] from the prior art also did not reveal the signs claimed in the characterizing part of the formula.

The invention is illustrated by drawings, which schematically depict:

in FIG. 1 is a fragment of an assembly diagram of a crystal with a substrate before soldering;

in FIG. 2 is a fragment of a circuit for connecting a crystal to a substrate using the developed method.

The isolation method during the installation of inverted crystals is implemented as follows.

Ready crystals 1 with contact columns 2 (Fig. 1), for example, made of gold on the front surface of crystal 1, enter the assembly. Gold contact columns are formed on the contact pads of crystal 1 as a part of the plate using one of the modifications of the thermocompression ball welding method, used in the formation of a butt joint of gold butt At the same time, on the upper part of the ball remains a pointed protrusion (a section of wire break).

In the traditional method of creating contact columns on a crystal of gold wire, deformation of a pointed protrusion on a contact column of gold using mechanical pressure is used. This operation is necessary to create a flat surface and level the height of all contact posts located on the chip.

An adhesive tape 4 having holes 5 is placed between the crystal 1 and the substrate 3, the pattern of which is a mirror image of the location of the contact posts 2 on the crystal 1. The tape 4 of type 3M is made in accordance with the quality system and registered with ISO 9001.

The substrate 3 is made separately, metallization is formed on the substrate on the contact pads 6 from the solder 7 of a given thickness. The thickness of the solder on the contact pads of the substrate is chosen depending on the height of the contact posts on the chip, the thickness of the tape and the gap between the contact pillar of the crystal and the hole in the adhesive tape.

When assembling, the contact posts 2 of the crystal 1 through holes 5 in the adhesive tape 4 are combined with solder 7 located on the contact pad 6 of the substrate 3 (Fig. 2). After assembly, the device is placed on a stand in a vacuum chamber, heated to the melting temperature of the solder and at the same time external pressure is applied to the crystal. When heated to a soldering temperature and the corresponding pressure on the crystal, the solder 7 melts. In this case, the entire surface of the contact column 2 is wetted with solder and the gap between the contact column 2 and the hole 5 in the adhesive tape 4 is filled, forming a sealed solder joint 8 between the crystal 1 and the substrate 3. A tight connection of the tape 4 with the surfaces 9 of the crystal and 10 of the substrate with the absence in the connecting gap between the crystal and the substrate of air gaps in the form of pores. The absence of pores in the connecting gap between the crystal and the substrate increases the heat transfer from the crystal to the substrate.

Based on the foregoing, it was concluded that the use of the proposed insulation method during the installation of inverted crystals provides the following advantages compared to existing methods:

1. The cost of manufactured products is reduced;

2. The heat sink from the crystal to the substrate increases.

Information sources

1. Semiconductor device and method of its manufacture with assembly by the inverted crystal method. Semiconductor device utilizing a face - down bonding and a method for manufacturing the same: US Pat. 5071787 USA, MKI ⁵ H01L 22/44 / Mori Miki, Saito Masayuki; K.K., Toshiba. - No. 477504; Claim 02/09/90; Publ. 12/10/91.

2. Novikov A. Conference “Improving the production of electronic equipment using mixed and lead-free soldering technologies [Text] / A. Novikov // Technologies in the electronic industry, 2009. No. 4, p.14.

Claims (4)

1. The method of isolation during installation of inverted crystals, including the assembly, which receives crystals with contact columns and substrates with metallization on contact pads from solder of a given thickness, which consists in the fact that an adhesive tape is placed between the crystal and the substrate, which has holes, the figure of which is mirroring the location of the contact columns on the crystal, during assembly, the contact columns of the crystal through the holes in the tape are combined with the solder of the contact pads on the substrate, then the aiku in vacuum, when heated to the soldering temperature and pressure on the crystal, the solder melts, and the entire surface of the contact columns of the crystal is wetted with solder, as a result of which the gap between the contact columns and the holes in the adhesive tape is filled, since the thickness of the tape is commensurate with the distance between the crystal and the substrate, then under the pressure of the crystal and at the soldering temperature there is a tight connection of the tape with the surfaces of the crystal and the substrate, which excludes not only the spreading of solder on the surfaces of the crystal and the substrate and short circuit between the contacts of the device, but also the formation of pores on the border of the tape with soldered surfaces of the crystal and the substrate. 2. The method according to p. 1, characterized in that they use type 3M adhesive tape between the crystal and the substrate. 3. The method according to p. 1, characterized in that the thickness of the solder on the contact pads of the substrate is selected depending on the height of the contact columns on the crystal, the thickness of the tape and the gap between the contact column of the crystal and the hole in the adhesive tape. 4. The method according to p. 1, characterized in that, in order to reduce (exclude) the pores in the "crystal - substrate" gap, the soldering is carried out in vacuum.

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