CN113641047A

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Info

Publication number: CN113641047A
Application number: CN202110914250.6A
Authority: CN
Inventors: 刘爱军; 吴玉森; 格培文
Original assignee: Omnivision Semiconductor Shanghai Co Ltd
Current assignee: Omnivision Semiconductor Shanghai Co Ltd
Priority date: 2021-08-10
Filing date: 2021-08-10
Publication date: 2021-11-12
Anticipated expiration: 2041-08-10
Also published as: CN113641047B

Abstract

The invention provides a flexible board packaging structure and an LCOS device. In the soft board packaging structure, the flexible circuit board comprises a first flexible portion and a second flexible portion which are connected with each other, a first contact pad is arranged on the front face of the first flexible portion, the reinforcing plate is bonded with the back face of the second flexible portion, a second contact pad is arranged on one side, facing the front face of the first flexible portion, of the chip module, the second contact pad is arranged opposite to the first contact pad, and the conductive adhesive is arranged between the first flexible portion and the chip module and is electrically connected with the first contact pad and the second contact pad respectively. After high and low temperature impact, the first flexible part can absorb internal stress generated by shrinkage of the conductive adhesive through swinging, and the contact surface structure of the conductive adhesive is protected, so that the resistance value between the first contact pad and the second contact pad is stable, and the reliability of the soft board packaging structure is improved. The LCOS device comprises the soft plate packaging structure.

Description

Flexible board packaging structure and LCOS device

Technical Field

The invention relates to the technical field of semiconductors, in particular to a flexible board packaging structure and an LCOS device.

Background

Liquid Crystal On Silicon (LCOS) is a reflective Liquid Crystal micro panel display technology, and has the characteristics of high light utilization efficiency, small volume, high aperture ratio, mature manufacturing technology and the like. When the LCOS chip manufactured by a cell process is packaged with a Flexible Printed Circuit (FPC), the back of the portion of the flexible printed circuit to be electrically connected to the LCOS chip is usually bonded to a rigid stiffener for fixation, and then aligned with the LCOS chip and electrically connected to the LCOS chip by disposing a conductive adhesive in a corresponding area, so that the obtained package structure is a complete circuit system.

Fig. 1 is a front view of a conventional LCOS package structure. Fig. 2 is a left side view of the LCOS package structure of fig. 1. Fig. 3 is a schematic plan view of a flexible circuit board used in an LCOS package structure. As shown in fig. 1 to 3, one conventional LCOS package structure includes an LCOS chip 12 'and aflexible circuit board 11 electrically connected to each other, wherein theflexible circuit board 11 includes a first flexible portion 111 electrically connected to the LCOS chip 12' through aconductive paste 13, and a secondflexible portion 112 contacting the LCOS chip 12 'and electrically connected to the LCOS chip 12' through a metal wire. The first flexible portion 111 has afirst contact pad 113 on a front surface thereof, and theconductive paste 13 covers thefirst contact pad 113 and is electrically connected to a second contact pad 14 (e.g. a pad) on the LCOS chip 12'. The back surface of theflexible circuit board 11 is provided with areinforcing plate 15 for supporting theflexible circuit board 11, thereinforcing plate 15 and theflexible circuit board 11 are fixed by adhesion, and an adhesive 16 between thereinforcing plate 15 and theflexible circuit board 11 is distributed over the entire range of the back surfaces of the first flexible portion 111 and the secondflexible portion 112 of theflexible circuit board 11.

However, it is found that the resistance of the LCOS package structure at theconductive paste 13 increases after high and low temperature impact, resulting in reduced reliability.

Disclosure of Invention

Regarding the problem that the impedance of theconductive adhesive 13 is increased after the conventional LCOS package structure is impacted by high and low temperatures, so that the reliability is reduced, the inventors have found through intensive research, the reason for this is that the high and low temperature impacts during and after the packaging process form a cold and hot impact on the colloid of theconductive paste 13, resulting in the formation of internal stress in the connection structure of theconductive paste 13 with theflexible circuit board 11 and the LCOS chip 12', the structure of the contact surface between theconductive paste 13 and the LCOS chip 12' (here, for example, the contact surface with the second contact pad 14) is also easily changed under stress, so that the adhesive force of theconductive paste 13 is deteriorated, i.e. a deterioration of the bonding force between thefirst contact pad 113 and theconductive paste 13 and thesecond contact pad 14 as in figure 1, so that the resistance between thefirst contact pad 113 and thesecond contact pad 14 is increased, which affects the reliability of the LCOS package structure.

In order to solve the above problems, the present invention provides a flexible board package structure and an LCOS device including the flexible board package structure.

In order to achieve the above object, an aspect of the present invention provides a flexible printed circuit board package structure, including:

the flexible circuit board comprises a first flexible part and a second flexible part which are connected with each other, and a first contact pad is arranged on the front surface of the first flexible part;

the reinforcing plate is arranged on the back surface of the flexible circuit board and is bonded with the back surface of the second flexible part;

the chip module is provided with a second contact pad facing to one side of the front surface of the first flexible part, and the second contact pad is opposite to the first contact pad; and

and the conductive adhesive is arranged between the first flexible part and the chip module and is electrically connected with the first contact pad and the second contact pad respectively.

Optionally, the first flexible portion includes a plurality of side edges extending in different directions, wherein some of the side edges are connected to the second flexible portion, and some of the side edges are edges of the flexible circuit board.

Optionally, the first flexible portion is connected to the second flexible portion by only one of the side edges.

Optionally, the chip module is disposed right above the flexible circuit board, and a lower surface of the chip module is attached to the front surface of the second flexible portion.

Optionally, the area of the front surface of the first flexible portion is smaller than the area of the front surface of the second flexible portion.

Optionally, the second contact pad is a solder bump disposed on the chip module.

The invention also provides an LCOS device which comprises the soft plate packaging structure, wherein the chip module is an LCOS chip.

Optionally, the LCOS chip includes a silicon substrate, a liquid crystal layer, and a glass cover plate stacked in sequence; the glass cover plate and the silicon substrate are arranged in a stacked and staggered mode, and the second contact pads are arranged on staggered positions of the glass plate and the silicon substrate.

In the flexible board package structure and the LCOS device of the present invention, the flexible circuit board includes a first flexible portion and a second flexible portion connected to each other, a first contact pad is disposed on a front surface of the first flexible portion, the stiffener is disposed on a back surface of the flexible circuit board and is bonded to a back surface of the second flexible portion, the chip module has a second contact pad disposed on a side facing the front surface of the first flexible portion, the second contact pad is disposed opposite to the first contact pad, and the conductive adhesive is disposed between the first flexible portion and the chip module and electrically connected to the first contact pad and the second contact pad, respectively. After the high low temperature strikes, the conducting resin easily contracts and produces the internal stress, because the reinforcing plate bonds mutually with the back of the flexible portion of second and does not bond mutually with first flexible portion, promptly first flexible portion can for the flexible portion of second with the reinforcing plate swing to this internal stress can be released (or absorbed) through the swing in the first flexible portion of flexible circuit board, and the contact surface structure that helps protecting the conducting resin does not receive stress failure, and it is right to reduce the internal stress the influence of the adhesive force of conducting resin improves first contact pad with resistance value stability between the second contact pad improves the flexible board packaging structure with the reliability of LCOS device.

Drawings

Fig. 1 is a front view of a conventional LCOS package structure.

Fig. 2 is a left side view of the LCOS package structure of fig. 1.

Fig. 3 is a schematic plan view of a flexible circuit board used in an LCOS package structure.

Fig. 4 is a schematic diagram of a flexible printed circuit board package structure according to an embodiment of the invention.

Fig. 5 is a schematic plan view of a flexible circuit board according to an embodiment of the invention.

Fig. 6 is a schematic diagram of a flexible printed circuit board package structure after high and low temperature impact according to an embodiment of the invention.

Fig. 7 is a box diagram of the resistance value of a conventional LCOS package structure after high and low temperature impact testing.

Fig. 8 is a box diagram of the resistance value of the flexible printed circuit board package structure after the high and low temperature impact test according to an embodiment of the invention.

Description of reference numerals: 11-a flexible circuit board; 111-a first flexible portion; 112-a second flexible portion; 113-a first contact pad; 114-a third flexible portion; 116-a third contact pad; 12-a chip module; 12' -LCOS chip; 121-a silicon substrate; 122-a glass cover plate; 13-conductive glue; 14-a second contact pad; 15-a reinforcing plate; 16-a binder; 17-a connector; 18-metal wire.

Detailed Description

The flexible board package structure and the LCOS device according to the present invention are further described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.

Example one

In order to absorb the internal stress generated after the high and low temperature impact (i.e. the cold and hot impact), protect the contact surface structure of the conductive adhesive from being damaged by the stress, and improve the reliability of the package structure, the present embodiment provides a flexible board package structure. The flexible board packaging structure comprises a flexible circuit board, a reinforcing plate, a chip module and conductive adhesive.

Specifically, the flexible circuit board includes a first flexible portion and a second flexible portion that are connected to each other, and a front surface of the first flexible portion is provided with a first contact pad. The reinforcing plate is arranged on the back surface of the flexible circuit board and is bonded with the back surface of the second flexible part. The chip module is provided with a second contact pad on one side facing the front surface of the first flexible portion, and the second contact pad is opposite to the first contact pad. The conductive adhesive is arranged between the first flexible portion and the chip module and is electrically connected with the first contact pad and the second contact pad respectively.

In the present embodiment, the Flexible Printed Circuit (FPC) is also called a Flexible Circuit board or a Flexible Circuit board, and is preferred because of its excellent characteristics such as light weight, thin thickness, and free bending and folding.

Fig. 4 is a schematic diagram of a flexible printed circuit board package structure according to an embodiment of the invention. Fig. 5 is a schematic plan view of a flexible circuit board according to an embodiment of the invention. As shown in fig. 4 and 5, theflexible circuit board 11 includes a first flexible portion 111 and a secondflexible portion 112, the first flexible portion 111 and the secondflexible portion 112 are connected to each other, a front surface of the first flexible portion 111 is provided with afirst contact pad 113, a surface (e.g., an upper surface) of thefirst contact pad 113 is exposed at the front surface of theflexible circuit board 11, and thefirst contact pad 113 is, for example, a metal contact pad.

Thestiffener 15 is disposed on the back surface of theflexible circuit board 11 and supports the flexible circuit board, so that theflexible circuit board 11 can have a flat surface, which facilitates assembly of thechip module 12 and theflexible circuit board 11.

As an example, thereinforcing plate 15 supports the first flexible portion 111 and the secondflexible portion 112 of theflexible circuit board 11. The edge of thereinforcing plate 15 may be beyond the edges of the first flexible portion 111 and the secondflexible portion 112 so that the reinforcingplate 15 may sufficiently support the first flexible portion 111 and the secondflexible portion 112.

The reinforcingplate 15 may be a ceramic plate or a stainless steel plate. But not limited thereto, in other embodiments, thestiffener 15 may be made of other materials as long as thestiffener 15 has the rigidity requirement and does not affect the performance of the flexible board package structure.

In the present embodiment, the back surface of the secondflexible portion 112 is bonded to the reinforcingplate 15 with, for example, an adhesive 16, and the first flexible portion 111 is not bonded to the reinforcingplate 15 and is in a separable state, so that the first flexible portion 111 of theflexible circuit board 11 can swing (slightly swing) with respect to the secondflexible portion 112 and the reinforcingplate 15.

In this embodiment, the front area of the first flexible portion 111 may be smaller than the front area of the secondflexible portion 112, and correspondingly, the back area of the first flexible portion 111 may be smaller than the back area of the secondflexible portion 112. The back surface of the secondflexible portion 112 is fixed to the surface of the reinforcingplate 15 facing theflexible circuit board 11 by an adhesive 16, and theflexible circuit board 11 can be fixed to the reinforcingplate 15, and the adhesive 15 is not provided between the first flexible portion 111 and the reinforcingplate 15, and the first flexible portion 111 can swing relative to the secondflexible portion 112 and the reinforcingplate 15, and the fixed area (i.e., the back surface of the second flexible portion 112) of theflexible circuit board 11 is larger than the swing area (i.e., the back surface of the first flexible portion 111), which is helpful for improving the bonding reliability between theflexible circuit board 11 and the reinforcingplate 15.

As shown in fig. 5, theflexible circuit board 11 may further include a strip-shaped thirdflexible portion 114, one end of the thirdflexible portion 114 is connected to the secondflexible portion 112, and the other end of the thirdflexible portion 114 may be provided with aconnector 17. In this embodiment, the strip-shaped thirdflexible portion 114 may be a flexible flat cable portion. External signals can be transmitted to thechip module 12 through theconnector 17 and theflexible circuit board 11, or signals in thechip module 12 can be transmitted through theflexible circuit board 11 and theconnector 17.

It should be noted that theflexible circuit board 11 of the present embodiment is a one-piece circuit board, and for convenience of description, different regions of theflexible circuit board 11 are defined as the first flexible portion 111, the secondflexible portion 112, and the thirdflexible portion 114. That is, in other embodiments, theflexible circuit board 11 may be divided in other manners, and the names defined by the different divided areas may be different.

As shown in fig. 4, asecond contact pad 14 is disposed on a side of thechip module 12 facing the front surface of the first flexible portion 111, thesecond contact pad 14 is disposed opposite to thefirst contact pad 113, and theconductive adhesive 13 is disposed between the first flexible portion 111 and thechip module 12 and electrically connected to thefirst contact pad 113 and thesecond contact pad 14, respectively.

Specifically, theconductive paste 13 may be composed of a resin matrix, conductive particles, a dispersion additive, an auxiliary agent, and the like. The resin matrix may include epoxy resins, acrylate resins, polyvinyl chloride, and the like. The conductive particles may be powders of gold, silver, copper, aluminum, zinc, iron, nickel, and graphite and some conductive compounds. Theconductive adhesive 13 is easily shrunk after cold and heat shock to generate internal stress.

Thechip module 12 may be an LCOS chip. The die set 12 may include asilicon substrate 121, a liquid crystal layer (not shown), and aglass cover plate 122, which are sequentially stacked. Theglass cover plate 122 and thesilicon substrate 121 may be stacked and staggered, and thesecond contact pads 14 are disposed at staggered positions of theglass cover plate 122 and thesilicon substrate 121. Thesecond contact pad 14 may be a solder bump disposed on the chip module 12 (specifically, disposed on a surface of theglass cover plate 122 facing the first flexible portion). The material of the solder bump may include a lead-tin alloy, a tin-silver alloy, or a tin-silver-copper alloy.

Theglass cover plate 122 may be a conductive glass plate. The conductive glass plate may be formed by plating a conductive film, such as an Indium Tin Oxide (ITO) film, onto an insulating glass surface. Wherein the surface of theglass cover plate 122 provided with the conductive film may face theflexible circuit board 11.

A dam (not shown) may be further disposed between thesilicon substrate 121 and theglass cover plate 122, and the dam may surround the liquid crystal layer to seal the liquid crystal layer between thesilicon substrate 121 and theglass cover plate 122.

A pixel array may be formed on a surface of thesilicon substrate 121 facing theglass cover plate 122. In one embodiment, thesilicon substrate 121 may be an Integrated Circuit (IC) driver chip electrically connected to individual pixels of the pixel array.

As shown in fig. 4, in this embodiment, thechip module 12 may be disposed right above theflexible circuit board 11, and a lower surface of thechip module 12 may be attached to a front surface of the secondflexible portion 112. Specifically, the lower surface of thesilicon substrate 121 in the chip module may be attached to the front surface of the secondflexible portion 112.

As shown in fig. 5, a plurality ofthird contact pads 116 may be further disposed on the secondflexible portion 112. Referring to fig. 4 and 5, thesilicon substrate 121 and the secondflexible portion 112 may be electrically connected bymetal wires 18, and themetal wires 18 are respectively connected to thethird contact pads 116 and corresponding conductive pads on the upper surface of thesilicon substrate 121. In this embodiment, themetal wire 18 may be a gold wire. Thesilicon substrate 121 and the secondflexible portion 112 may be interconnected by a wire bonding process. In order to protect themetal wire 18 and improve the reliability of interconnection between thesilicon substrate 121 and the secondflexible portion 112, a protective adhesive may be further disposed on the periphery of themetal wire 18.

Fig. 6 is a schematic diagram of a flexible printed circuit board package structure after high and low temperature impact according to an embodiment of the invention. As shown in fig. 6, after the flexible board package structure is subjected to high and low temperature impact, theconductive adhesive 13 is easily shrunk to generate internal stress, and since the adhesive 16 is not disposed between the first flexible portion 111 of theflexible circuit board 11 and the reinforcingplate 15, the first flexible portion 111 can absorb the internal stress of theconductive adhesive 13 by swinging (e.g., slightly swinging upward), which helps to protect the contact surface structure of the conductive adhesive 13 from stress damage, so that the resistance value between theconductive adhesive 13 and theglass cover 122 is stable.

Fig. 7 is a box-type schematic diagram of the resistance value of a conventional LCOS package structure after high and low temperature impact testing. As shown in fig. 7, after 1500 cycles of high and low temperature impact test (TC test), the resistance between the first contact pad on the first flexible portion (i.e., the conductive adhesive connection region) of the flexible circuit board and the glass cover plate of the conventional LCOS package structure increases to about 200 kohm. Fig. 8 is a box-type schematic diagram of the resistance value of the flexible printed circuit board package structure after the high and low temperature impact test according to an embodiment of the invention. As shown in fig. 8, after 1500 cycles of high and low temperature impact tests, the resistance between thefirst contact pad 113 on the first flexible portion 111 of theflexible circuit board 11 and theglass cover plate 122 is about 50Ohm (much less than 200K Ohm). Experiment results show that in the flexible board package structure of the present embodiment, the first flexible portion 111 of theflexible circuit board 11 can absorb internal stress generated by shrinkage of the conductive adhesive 13 through swinging, which is helpful for reducing the influence of the internal stress on the adhesive force of theconductive adhesive 13 and improving the stability of the resistance value between theconductive adhesive 13 and theglass cover plate 122.

In the flexible board package structure of this embodiment, theflexible circuit board 11 includes a first flexible portion 111 and a secondflexible portion 112 connected to each other, afirst contact pad 113 is disposed on a front surface of the first flexible portion 111, thestiffener 15 is disposed on a back surface of theflexible circuit board 11 and is bonded to a back surface of the secondflexible portion 112, asecond contact pad 14 is disposed on a side of thechip module 12 facing the front surface of the first flexible portion 111, thesecond contact pad 14 is disposed opposite to thefirst contact pad 113, and theconductive adhesive 13 is disposed between the first flexible portion 111 and thechip module 12 and electrically connected to thefirst contact pad 113 and thesecond contact pad 14, respectively. After the flexible board package structure is subjected to high and low temperature impact, theconductive adhesive 13 is easy to contract to generate internal stress, and the reinforcing plate is bonded to the back surface of the second flexible portion but not bonded to the first flexible portion 111, that is, the first flexible portion 111 can swing relative to the secondflexible portion 112 and the reinforcingplate 15, and the internal stress can be released (absorbed) through the swing of the first flexible portion 111 of the flexible circuit board, so that the structure of the contact surface of the conductive adhesive 13 (for example, the contact surface of theconductive adhesive 13 and the second contact pad 14) is protected from stress damage, the influence of the internal stress on the adhesive force of theconductive adhesive 13 is reduced, the stability of the resistance value between thefirst contact pad 113 and thesecond contact pad 14 is improved, and the reliability of the flexible board package structure is further improved.

Example two

The embodiment provides an LCOS device, which includes a flexible printed circuit package structure in the first embodiment, the flexible printed circuit package structure includes aflexible circuit board 11, astiffener 15, achip module 12 and aconductive adhesive 13, wherein thechip module 12 is an LCOS chip.

In the flexible board package structure, theflexible circuit board 11 includes a first flexible portion 111 and a secondflexible portion 112 connected to each other, afirst contact pad 113 is disposed on a front surface of the first flexible portion 111, thestiffener 15 is disposed on a back surface of theflexible circuit board 11 and is bonded to a back surface of the secondflexible portion 112, asecond contact pad 14 is disposed on a side of the chip module facing the front surface of the first flexible portion, thesecond contact pad 14 is disposed opposite to thefirst contact pad 113, and theconductive adhesive 13 is disposed between the first flexible portion 111 and thechip module 12 and electrically connected to thefirst contact pad 113 and thesecond contact pad 14, respectively.

The LCOS chip may include asilicon substrate 121, a liquid crystal layer (not shown in the figure), and aglass cover plate 122 stacked in sequence, where theglass cover plate 122 and thesilicon substrate 121 are stacked and staggered, and the staggered positions of theglass plate 122 and thesilicon substrate 121 may be provided with thesecond contact pad 14.

Because the first flexible portion 111 of flexible circuit board among the soft board packaging structure with it is separable state not to bond between the reinforcingplate 15, the internal stress that conductingresin 13 produced after high low temperature strikes can pass through the swing of first flexible portion 111 and absorbed, helps protecting the contact surface structure of conductingresin 13 and does not receive the internal stress destruction, makes conductingresin 13 with the resistance value between theglass apron 122 is stable, can improve the reliability of soft board packaging structure, and then can improve the reliability of LCOS device.

The above description is only for the purpose of describing the preferred embodiments of the present invention and is not intended to limit the scope of the claims of the present invention, and any person skilled in the art can make possible the variations and modifications of the technical solutions of the present invention using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention, and therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention belong to the protection scope of the technical solutions of the present invention.

Claims

1. A flexible board package structure, comprising:

2. The package structure of claim 1, wherein the first flexible portion comprises a plurality of side edges extending in different directions, wherein a portion of the side edges are connected to the second flexible portion, and a portion of the side edges are edges of the flexible circuit board.

3. The package structure of claim 2, wherein the first flexible portion is connected to the second flexible portion by only one of the side edges.

4. The package structure of claim 1, wherein the chip module is disposed directly above the flexible circuit board, and a lower surface of the chip module is attached to a front surface of the second flexible portion.

5. The flexible board packaging structure of claim 1, wherein the area of the front surface of the first flexible portion is smaller than the area of the front surface of the second flexible portion.

6. The flexible board package structure of claim 1, wherein the second contact pad is a solder bump disposed on the chip module.

7. An LCOS device, comprising the flexible printed circuit board package structure of any one of claims 1 to 6, wherein the chip module is an LCOS chip.

8. The LCOS device of claim 7, wherein said LCOS chip comprises a silicon substrate, a liquid crystal layer and a glass cover plate, which are stacked in sequence; the glass cover plate and the silicon substrate are arranged in a stacked and staggered mode, and the second contact pads are arranged on staggered positions of the glass plate and the silicon substrate.