WO2007017341A1

WO2007017341A1 - Fluxing encapsulants casting resins for dca applications, based on cationically curable epoxy resins

Info

Publication number: WO2007017341A1
Application number: PCT/EP2006/064258
Authority: WO
Inventors: Stefan Czwienczek; Barbara Lehner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2005-08-11
Filing date: 2006-07-14
Publication date: 2007-02-15

Abstract

The invention relates to a method for soldering electronic components according to the direct chip attachment method. According to said method, an underfill resin is used during the soldering process. The underfill resin comprises sulphonium salts with the general structure indicated in formula (I).

Description

description

Fluxing encapsulants - casting resins for DCA applications based on cationic curable epoxy resins

The present invention relates to a method for soldering electronic components according to the direct chip attachment method, the underfill resin for soldering and an electronic component soldered thereto.

The term flip-chip technology, also called direct chip attachment (DCA) technique, denotes a method for connecting semiconductor devices to circuit carriers, for. B. printed circuit boards. The so-called bumps (contact mound) is used by the flip chip technology to connect unhoused chips to the electrical connections of the printed circuit board. The special feature of this method is that the mechanical and the electrical contact is made directly and not as usual by bonding wires or chip package. Since the flip-chip technology allows a high packing density of components on a circuit carrier, a lot of space and weight can be saved. The flip-chip technology is therefore particularly well suited for the production of microsystems.

In the prior art, it is known to fill the gap between the electronic component and the substrate with a reaction resin and thus to distribute the stress forces by the different coefficients of thermal expansion of the components of the solder pads on the entire surface under the device.

In the case of the "capillary underfill", the underfill material is metered as beads at up to three edges of the already soldered component and sucked under the chip by capillary forces Additional underfill material is applied to the last edge to obtain a uniform edge around the chip However, the procedure involves a great deal of effort, additional work steps and thus high costs.

In addition to the capillary underfill process, a combined soldering and encapsulation process has been developed in which the resin is either applied to the substrate or to the device prior to soldering Work step performed in the reflow oven.

Commercially available underfill resins having flux properties are described, for example, by Loctite (3594), Cookson (Staychip NUF-2070E, NUF-2071E, NUF-2073E), Kester (VO9003-53 - / - 6C, ERE 74), Nagase (T693 / R3902, T693 / UFR107N) and Dexter Hysol FF2000, FF220) on the market. Such resin formulations rely on anhydride-curing epoxy resins whose reactivity is adjusted with suitable accelerators. These formulations are insufficiently adapted in their reactivity to specified on the component side soldering profiles. The flux is usually added in the form of organic acids. However, such resin mixtures require storage at -40 ⁰ C.

Another possibility for initiating thermal curing of epoxy resins is disclosed in EP 889 361 (Siemens AG). This document describes sulfonium salts as new initiators which are suitable for cationic polymerization and have the following structure:

where the following applies R ¹ and R ² are alkyl or cycloalkyl or together with the S atom form a heterocyclic ring, R ³ is H or alkyl,

R ⁴ , R ⁵ , R ⁶ and R ⁷ are H, alkyl or alkoxy, X ^" is a non-nucleophilic anion.

The patent EP 889 361 is in a different technical field than the present invention, since applications in the soldering process in general or in the direct chip attachment method are not described.

There is thus a need for improvements in the art. In particular, there is a need for new methods for soldering electronic components according to the direct chip attachment method, whose underfill resin formulations are storable at room temperature, have flux properties and at the same time contain the lowest possible number of components for cost reasons.

This object is achieved in accordance with the invention by a method for soldering electronic components according to the direct chip attachment method, wherein a underfill resin is used for soldering, wherein the underfill resin comprises sulfonium salts which have the following structure I:

i being

X ^"is a non-nucleophilic anion selected from the group comprising hexafluoroantimonate, hexafluoroarsenate, hexafluorophosphate, tetraphenylborate, tetra (perfluorophenyl) borate and / or trifluoromethanesulfonate;

R ¹ and R ^{2 are} alkyl having 1 to 9 C atoms, cycloalkyl having 4 to 9

C atoms are or together form a divalent aliphatic grouping having 4 to 7 C atoms; R is H or alkyl of 1 to 9 carbon atoms;

R ^{4 is} aryl, phenyl, naphthyl or R ^{4 has} the following structure

II has:

II where

R is 4-methoxy-naphtho-1-yl or R has the following structure III:

III being

R ⁶ , R ⁷ , R ⁸ , R ⁹ independently of one another are H, alkyl having 1 to 9

C atoms or alkoxy having 1 to 9 carbon atoms.

Electronic components in the sense of this invention include in particular chip-equipped circuit carriers or printed circuit boards.

Cationic initiators, such as the sulfonium salt-based ones mentioned above, which are used for the UV and thermal curing of epoxy resins, form Lewis acids on UV irradiation or on heating. Without being bound to any particular theory, it is believed that a sulfur-carbon bond is cleaved and a carbocation is formed or a proton is split off in a subsequent reaction.

It has now surprisingly been found that these Lewis acids can also act as activators in the sense of fluxes. In the method according to the invention of the direct chip attachment method, the underfill resin with fluxing properties (fluxing encapsulant) is metered onto the substrate in such a way that all connection pads required for soldering are covered. The bumped electronic component is positioned thereon, displacing excess resin to the outer edges of the component. The assembly is then soldered in a reflow oven.

The initiators of the resin formulations used herein undergo bond scission at temperatures below the melting ranges of the solders. In doing so, they release Lewis acids, which remove the passivating oxide layer on the metallization and on the solder and act as a flux. This allows the solder to completely wet the pads.

At the same time, however, the Lewis acids also initiate the hardening process of the epoxy resins surrounding the solder joints. In the melting range of the solder, the reaction conversion of the resin hardening is desirably very small. However, just above the melting temperature of the solder, the curing proceeds very rapidly and forms a stabilizing layer between the substrate and the component.

The resins adhere well to the device, the substrate, the tracks and the solder joints. During curing, they only diminish minimally; their low coefficient of thermal expansion (CTE) thus minimizes the thermal stress that acts on the assembly in the temperature cycle test.

With the combined soldering and encapsulation process when using fluxing encapsulants cleaning of the solder joints after soldering and the capillary process to underfill the components is thus no longer necessary. The resin is applied either to the substrate or to the device prior to soldering. The soldering of the components and subsequent curing of the resin is carried out in one step. A further advantage of the method according to the invention is that the number of process steps is considerably lower in comparison to traditional sequence soldering and capillary underfill. For example, when assembling printed circuit boards, the number of steps decreases from the previous 7 to 3.

In one embodiment of the method according to the invention, the component mounted on the substrate is subjected to a time-dependent temperature profile in the reflow oven. It is important to ensure that a certain maximum temperature is not exceeded. The maximum temperature is determined by the thermal stability of the components and the curing profile of the resin. In the method according to the invention, the maximum temperature which is achieved during the soldering process is

> 150 ⁰ C to <200 ⁰ C, preferably> 160 ⁰ C to <190 ⁰ C, particularly preferably> 165 ⁰ C to ≤170 ⁰ C. An example is shown in Fig. 1, a time-dependent reflow temperature profile for a Sn-Bi Lot shown. It can be seen at the beginning of a gradual increase in temperature, which accelerates after about half of the residence time and reaches a maximum of 169 ⁰ C at a time of 6 minutes. After this maximum, the temperature drops sharply and has returned to room temperature within four minutes.

The solders used in the method according to the invention can be applied to the component, to the printed circuit board or both before soldering. The used solder is subject in principle no restrictions. It may be selected from the group comprising Pb-Sn, Ag-Sn-Pb, Sb-Sn-Pb, Au-Sn-Pb, In-Sn-Pb and / or Sn-Bi. It is preferably a Sn-Bi solder.

In one embodiment of the present invention, the sulfonium salt in the underfill resin is in a proportion of> 0.1 wt .-% to <20 wt .-%, preferably> 0.5 wt .-% to

<9 wt .-%, particularly preferably> 1 wt .-% to <6 wt .-% before. In a further embodiment of the present invention, the sulfonium salt in the underfilling resin releases from above a temperature of> 60 ⁰ C, preferably> 70 ⁰ C, more preferably> 80 ⁰ C Lewis acids.

In a further embodiment, the underfilling resin used in the method according to the invention can furthermore comprise additives for influencing the elasticity, for adjusting the thermal expansion, the flow properties and adhesion promoters. Thus, the underfill resin may comprise: elastomeric polymer, preferably carboxy-terminated butadiene-nitrile rubber; high-temperature thermoplastic polymer, preferably polyetherimide;

Filler, preferably fused silica, more preferably selected from the group comprising splintered and / or spherical

fused silica;

Rheology modifier, preferably polyacrylate; and / or epoxy-functionalized silane.

Bis-A epoxy resin suitable according to the invention is obtainable, for example, from Vantico under the trade name Araldit MY 790.

Carboxy-terminated butadiene nitrile rubber-containing bis-A-epoxy resin suitable according to the invention is obtainable, for example, from Vantico under the trade name Araldit CY 5995.

Polyetherimide suitable according to the invention is available, for example, from GE under the trade name Ultem 100.

Spherical fused silica suitable according to the invention is available, for example, from Denka under the trade name FB 44. According to the invention suitable splintered fused silica is, for example, by the company quartz works under the Han Silbond FW 61 EST or Silbond FW 600 EST are available.

Polyacrylate suitable according to the invention is available, for example, from Monsanto under the trade name Modaflow.

Epoxy-functionalized silane suitable according to the invention is obtainable, for example, from UCC under the trade name Silan A 187.

In a further embodiment of the present invention, underfilling resin used in the process according to the invention comprises the following constituents:> 60% by weight to <80% by weight, preferably> 65% by weight to <70% by weight, particularly preferably> 67% by weight from% to <69% by weight of a carbo-oxidised butadiene-nitrile rubber-containing bis-A epoxy resin;

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to

<2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt .-% Benyzlthiolanium hexafluoroantimonate;

> 20 wt .-% to <40 wt .-%, preferably> 25 wt .-% to <35 wt .-%, particularly preferably> 29 wt .-% to <31 wt .-% of a spherical quartz material;

> 0.01 wt .-% to <0.5 wt .-%, preferably> 0.05 wt .-% to <0.4 wt .-%, particularly preferably> 0.1 wt .-% to <0.3 wt .-% of a polyacrylate; and or

> 0.01 wt .-% to <0.5 wt .-%, preferably> 0.05 wt .-% to <0.4 wt .-%, particularly preferably> 0.1 wt .-% to <0.3 wt .-% of an epoxy-functionalized silane.

An example of a resin formulation used in the process according to the invention is given in the following Table 1: Table 1

* 1 Available for example from Vantico under the trade name Araldit CY 5995

* 2 For example, available from Denko under the trade name FB 44

* 3 Available for example from Monsanto under the trade name Modaflow

* 4 Available for example from the company UCC under the trade name Silan A 187

In a further embodiment of the present invention, the underfilling resin used in the process according to the invention comprises the following constituents:> 45% by weight to <60% by weight, preferably> 50% by weight to <55% by weight, particularly preferably> 52 % By weight to <53% by weight of a bis-A epoxy resin;

> 3 wt .-% to <8 wt .-%, preferably> 4 wt .-% to <7 wt .-%, particularly preferably> 5 wt .-% to <6 wt .-% of a polyetherimides mids;

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to

<2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt .-% S- [2- (4-methoxy-naphtho-1-yl) -2-oxo-ethyl] -dimethylsulfonium hexafluoroantimonate;

> 30 wt .-% to <45 wt .-%, preferably> 35 wt .-% to <40 wt .-%, particularly preferably> 37 wt .-% to <38 wt .-% of a first splintered quartz material;

> 0.5 wt .-% to <5 wt .-%, preferably> 1 wt .-% to <4 wt .-%, particularly preferably> 2 wt .-% to <3 wt .-% of a second splintered quartz Good;

≥O.Ol wt .-% to <0.5 wt .-%, preferably> 0.05 wt .-% to <0.4 wt .-%, particularly preferably> 0.1 wt .-% to <0.3 wt .-% of a polyacrylate; and or

≥O.Ol wt .-% to <0.5 wt .-%, preferably> 0.05 wt .-% to <0.4 wt .-%, particularly preferably> 0.1 wt .-% to <0.3 wt .-% of an epoxy-functionalized silane.

Another example of a resin formulation used in the process according to the invention is given in Table 2 below:

Table 2

* 1 Available for example from Vantico under the trade name Araldit MY 790. * 2 For example, available from GE under the trade name Ultem 100.

* 3 For example, available from Quarzwerke under the trade name Silbond FW 61 EST.

* 4 For example, available from Quarzwerke under the trade name Silbond FW 600 EST.

* 5 For example, available from the company Monsanto under the trade name Modaflow.

* 6 Available for example from the company UCC under the trade name Silan A 187.

The subject matter of the present invention furthermore relates to a backfill resin comprising the following constituents: sulfonic acid salts which have the following structure I:

i being

R ¹ and R ^{2 are} alkyl having 1 to 9 C atoms, cycloalkyl having 4 to 9

C atoms are or together form a divalent aliphatic grouping having 4 to 7 C atoms;

R ^{3 is} H or alkyl of 1 to 9 C atoms;

R ^{4 is} aryl, phenyl, naphthyl or R ^{4 has} the following structure

II has:

II where

R ^{5 is} 4-methoxy-naphtho-1-yl or R ^{5 is} the following structure

III has:

III being

R ⁶ , R ⁷ , R ⁸ , R ⁹ independently of one another are H, alkyl having 1 to 9 C atoms or alkoxy having 1 to 9 C atoms; elastomeric polymer; high temperature thermoplastic polymer; and optionally further additives selected from the group comprising filler, rheology modifier and / or epoxy-functionalized silane.

The elastomeric polymer used is advantageously carboxy-terminated butadiene-nitrile rubber.

As a high-temperature thermoplastic polymer can be advantageously use polyetherimide. Polyetherimide suitable according to the invention is available, for example, from GE under the trade name Ultem 100.

The filler may be selected from the group comprising fused quartz, more preferably selected from the group comprising splintered and / or spherical fused silica. Spherical fused silica suitable according to the invention is available, for example, from Denka under the trade name FB 44. Splintered fused silica suitable according to the invention is available, for example, from Quarzwerke under the trade names Silbond FW 61 EST or Silbond FW 600 EST. As a rheology modifier it is advantageous to use a polyacrylate. Polyacrylate suitable according to the invention is available, for example, from Monsanto under the trade name Modaflow.

Suitable epoxy-functionalized silane which can be used according to the invention is obtainable, for example, from UCC under the trade name Silan A 187.

In a preferred embodiment of the present invention, the underfill resin comprises the following constituents:

> 60 wt .-% to <80 wt .-%, preferably> 65 wt .-% to <70 wt .-%, particularly preferably> 67 wt .-% to <69 wt .-% of a carboxy-terminated butadiene-nitrilkautschuk- containing bis-A epoxy resin;

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to <2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt .-% Benyzlthiolanium hexafluoroantimonate;

> 20% by weight to <40% by weight, preferably> 25% by weight to <35% by weight, particularly preferably> 29% by weight to <31% by weight, of a spherical quartz material;

Carboxy-terminated butadiene nitrile rubber-containing bis-A-epoxy resin suitable according to the invention is obtainable, for example, from Vantico under the trade name Araldit CY 5995. In a further advantageous embodiment of the present invention, the underfill resin comprises the following constituents:

> 45 wt .-% to <60 wt .-%, preferably> 50 wt .-% to <55 wt .-%, particularly preferably> 52 wt .-% to <53 wt .-% of a bis-A epoxy resin ;

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to <2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt .-% S- [2- ( 4-methoxynaphtho-1-yl) -2-oxo-ethyl] -dimethylsulfonium hexafluoroantimonate;

Bis-A epoxy resin suitable according to the invention is obtainable, for example, from Vantico under the trade name Araldit MY 790. The invention further relates to an electronic component, wherein the electronic component is soldered by means of a Unterfüllharzes according to the present invention.

Claims

claims

1. A method for soldering electronic components according to the direct chip attachment method, wherein a Unterfüllharz is used for soldering, characterized in that the Unterfüllharz comprises sulfonium salts, which have the following structure I:

in which

R ¹ and R ^{2 are} alkyl having 1 to 9 C atoms, cycloalkyl having 4 to 9 C atoms or together form a divalent aliphatic grouping having 4 to 7 C atoms; R ^{3 is} H or alkyl of 1 to 9 C atoms; R ^{4 is} aryl, phenyl, naphthyl or R ^{4 has} the following structure

II has:

II where

R ^{5 is} 4-methoxy-naphtho-1-yl or R ^{5 is} the following structure

III has:

in which R ⁶ , R ⁷ , R ⁸ , R ⁹ independently of one another are H, alkyl having 1 to 9 C atoms or alkoxy having 1 to 9 C atoms.

2. The method according to claim 1, characterized in that the maximum temperature which is achieved during the soldering process,

> 150 ⁰ C to <200 ⁰ C, preferably> 160 ⁰ C to <190 ⁰ C, more preferably> 165 ⁰ C to <170 ⁰ C.

3. Process according to claims 1 and 2, characterized in that the solder used is selected from the group comprising Pb-Sn, Ag-Sn-Pb, Sb-Sn-Pb, Au-Sn-Pb, In-Sn-Pb and / or Sn-Bi, preferably Sn-Bi.

4. The method according to claims 1 to 3, characterized in that the sulfonium salt in Unterfüllharz in a proportion of

≥O.l wt .-% to <20 wt .-%, preferably> 0.5 wt .-% to <9 wt .-%, particularly preferably> 1 wt .-% to <6 wt .-% is present.

5. The method according to claims 1 to 4, characterized in that the sulfonium salt in the Unterfüllharz from a temperature of> 60 ⁰ C, preferably> 70 ⁰ C, more preferably> 80 ⁰ C liberates Lewis acids.

6. The method according to claims 1 to 5, characterized in that the underfill resin further comprises the following constituents: elastomeric polymer, preferably carboxy-terminated butadiene

nitrile rubber; high-temperature thermoplastic polymer, preferably polyetherimide;

fused silica;

7. Process according to claims 1 to 6, characterized in that the underfilling resin comprises the following constituents: > 60 wt .-% to <80 wt .-%, preferably> 65 wt .-% to <70 wt .-%, particularly preferably> 67 wt .-% to <69 wt .-% of a carboxy-terminated butadiene-nitrilkautschuk- containing bis-A epoxy resin;

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to

<2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt .-%

Benyzlthiolanium hexafluoroantimonate;

> 20 wt .-% to <40 wt .-%, preferably> 25 wt .-% to

<35 wt .-%, particularly preferably> 29 wt .-% to <31 wt .-% of a spherical quartz material;

8. The method according to claims 1 to 1, characterized in that the underfill resin comprises the following components:> 45 wt .-% to <60 wt .-%, preferably> 50 wt .-% to <55 wt .-%, particularly preferably > 52 wt .-% to <53 wt .-% of a bis-A-epoxy resin;

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to <2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt .-% S- [2- ( 4-methoxynaphtho-1-yl) -2-oxo-ethyl] -dimethylsulfonium hexafluoroantimonate; > 30 wt .-% to <45 wt .-%, preferably> 35 wt .-% to <40 wt .-%, particularly preferably> 37 wt .-% to <38 wt .-% of a first splintered quartz material;

> 0.5 wt .-% to <5 wt .-%, preferably> 1 wt .-% to

<4 wt .-%, particularly preferably> 2 wt .-% to <3 wt .-% of a second splintered quartz material;

9. Electronic component, in particular chip-equipped circuit carrier, produced according to one of claims 1 to 8.

10. Underfill resin, comprising the following constituents:

Sulfonium salts which have the following structure I:

i being

X ^"is a non-nucleophilic anion selected from the group comprising hexafluoroantimonate, hexafluoroarsenate, hexafluorophosphate, tetraphenylborate, tetra (perfluorophenyl) borate and / or trifluoromethanesulfonate, R ¹ and R ^{2 are} alkyl having 1 to 9 C atoms, cycloalkyl having 4 to 9 C atoms are or together form a divalent aliphatic grouping having 4 to 7 C atoms, R ^{3 is} H or alkyl having 1 to 9 C atoms, R ^{4 is} aryl, phenyl, naphthyl or R ^{4 has} the following structure II:

II where

R ^{5 is} 4-methoxy-naphtho-1-yl or R ^{5 is} the following structure

III has:

III being

11. Underfoaming resin according to claim 10, comprising the following constituents:

> 0.5 wt .-% to <3.0 wt .-%, preferably> 1.0 wt .-% to <2.0 wt .-%, particularly preferably> 1.5 wt .-% to <1.7 wt ⁵ Benyzlthiolanium hexafluoroantimonate;

> 20% by weight to <40% by weight, preferably> 25% by weight to <35% by weight, particularly preferably> 29% by weight to <31% by weight, of a spherical quartz material; ≥O.Ol wt .-% to <0.5 wt .-%, preferably> 0.05 wt .-% to <0.4 wt .-%, particularly preferably ≥O .1 wt .-% to <0.3 wt .-% of a polyacrylate ; and or

≥O.Ol wt .-% to <0.5 wt .-%, preferably> 0.05 wt .-% to

<0.4 wt .-%, particularly preferably ≥O .1 wt .-% to <0.3 wt .-% of an epoxy-functionalized silane.

12. Underfill resin according to claim 10, comprising the following constituents:

≥O.Ol wt .-% to <0.5 wt .-%, preferably ≥0.05 wt .-% to <0.4 wt .-%, particularly preferably ≥O .1 wt .-% to <0.3 wt .-% of a polyacrylate ; and or

≥O.Ol wt .-% to <0.5 wt .-%, preferably ≥0.05 wt .-% to <0.4 wt .-%, particularly preferably ≥O .1 wt .-% to <0.3 wt .-% of an epoxy-functionalized silane.

13. Electronic component, wherein the electronic component is soldered by means of a Unterfüllharzes according to one of claims 10 to 12.