Disclosure of Invention
Regarding the problem that the reliability of the conventional LCOS package structure is reduced due to the increase of the impedance of the conductive adhesive 13 after the high and low temperature impact, the inventor has found that the reason is that the high and low temperature impact forms cold and hot impact on the adhesive of the conductive adhesive 13 during the packaging process and after the packaging is completed, which results in internal stress formed in the connection structure between the conductive adhesive 13 and the flexible circuit board 11 and the LCOS chip 12', and the contact surface (here, for example, the contact surface with the second contact pad 14) of the conductive adhesive 13 and the LCOS chip 12' is also easily changed under the stress, which results in the deterioration of the adhesive force of the conductive adhesive 13, that is, the bonding force between the first contact pad 113, the conductive adhesive 13 and the second contact pad 14 as in fig. 1 is deteriorated, so that the electrical resistance between the first contact pad 113 and the second 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 printed circuit package structure and an LCOS device including the same.
In order to achieve the above object, an aspect of the present invention provides a flexible board packaging structure, comprising:
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 adhered to the back surface of the second flexible part;
the chip module is provided with a second contact pad on one side of the front surface of the first flexible part, and the second contact pad is arranged opposite to the first contact pad; and
and the conductive adhesive is arranged between the first flexible part and the chip module and is respectively and electrically connected with the first contact pad and the second contact pad.
Optionally, the first flexible portion includes a plurality of sides extending in different directions, wherein the sides in a partial direction are connected to the second flexible portion, and the sides in a partial direction 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 directly above the flexible circuit board, and the lower surface of the chip module is attached to the front surface of the second flexible portion.
Optionally, the front surface area of the first flexible portion is smaller than the front surface area of the second flexible portion.
Optionally, the second contact pad is a solder bump disposed on the chip module.
Another aspect of the present invention further provides an LCOS device, where the LCOS device includes the above soft board packaging structure, and the chip module is an LCOS chip.
Optionally, the LCOS chip includes a silicon substrate, a liquid crystal layer, and a glass cover plate that are sequentially stacked; the glass cover plate and the silicon substrate are overlapped and staggered, and the staggered part of the glass plate and the silicon substrate is provided with the second contact pad.
In the flexible printed circuit package structure and the LCOS device, the flexible printed circuit comprises a first flexible part and a second flexible part which are connected with each other, 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 printed circuit and is adhered to the back surface of the second flexible part, a second contact pad is arranged on one side, facing the front surface of the first flexible part, 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 part and the chip module and is electrically connected with the first contact pad and the second contact pad respectively. The flexible printed circuit board is characterized in that the flexible printed circuit board is provided with a first flexible part and a second flexible part, wherein the first flexible part is arranged on the back surface of the first flexible part, the second flexible part is arranged on the back surface of the second flexible part, and the first flexible part is arranged on the back surface of the second flexible part.
Detailed Description
The flexible printed circuit package and the LCOS device according to the present invention will be described in further detail with reference to the accompanying drawings and examples. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for convenience and clarity in aiding in the description of embodiments of the invention.
Example 1
In order to absorb internal stress generated after high-low temperature impact (namely cold and hot impact), the contact surface structure of the conductive adhesive is protected from being damaged by the stress, the reliability of the packaging structure is improved, and the embodiment provides a soft board packaging structure. The soft board packaging structure comprises a flexible circuit board, a reinforcing plate, a chip module and conductive adhesive.
Specifically, 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 adhered to the back surface of the second flexible part. And a second contact pad is arranged on one side of the chip module, which faces the front surface of the first flexible part, and the second contact pad is arranged opposite to the first contact pad. The conductive adhesive is arranged between the first flexible part and the chip module and is respectively and electrically connected with the first contact pad and the second contact pad.
In this embodiment, the flexible circuit board (Flexible Printed Circuit, FPC) may be also referred to as a flexible circuit board or a flexible circuit board, and is favored in excellent characteristics such as light weight, thin thickness, free bending and folding.
Fig. 4 is a schematic view of a flexible printed circuit 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, the flexible circuit board 11 includes a first flexible portion 111 and a second flexible portion 112, the first flexible portion 111 and the second flexible portion 112 are connected to each other, a front surface of the first flexible portion 111 is provided with a first contact pad 113, a surface (e.g., an upper surface) of the first contact pad 113 is exposed on the front surface of the flexible circuit board 11, and the first contact pad 113 is, for example, a metal contact pad.
The reinforcing plate 15 is disposed on the back surface of the flexible circuit board 11 and supports the flexible circuit board, so that the flexible circuit board 11 may have a flat plane, facilitating assembly of the chip module 12 and the flexible circuit board 11.
As an example, the reinforcing plate 15 supports the first flexible portion 111 and the second flexible portion 112 of the flexible circuit board 11. The edges of the reinforcing plate 15 may be beyond the edges of the first and second flexible parts 111 and 112 so that the reinforcing plate 15 may sufficiently support the first and second flexible parts 111 and 112.
The reinforcing plate 15 may be a ceramic plate or a stainless steel plate. But is not limited thereto, in other embodiments, the reinforcing plate 15 may be made of other materials as long as the reinforcing plate 15 has rigidity that meets the requirements and does not affect the performance of the flexible board package structure.
In this embodiment, the back surface of the second flexible portion 112 is bonded to the reinforcing plate 15, for example, by an adhesive 16, and the first flexible portion 111 is not bonded to the reinforcing plate 15 but is in a separable state, so that the first flexible portion 111 of the flexible circuit board 11 can swing (slightly swing) with respect to the second flexible portion 112 and the reinforcing plate 15.
Specifically, the first flexible part 111 may include a plurality of sides extending in different directions, wherein part of the sides may be connected to the second flexible part 112, and part of the sides may be edges of the flexible circuit board 11. As shown in fig. 5, as an example, the front surfaces of the first flexible portion 111 and the second flexible portion 112 of the flexible circuit board 11 are rectangular, and only one side of the first flexible portion 111 is connected to the second flexible portion 112, so that the first flexible portion 111 has a high degree of freedom of movement, which is convenient for the first flexible portion 111 to absorb internal stress by swinging. However, the front shapes of the first flexible portion 111 and the second flexible portion 112 may be pentagonal, etc. in other embodiments, the first flexible portion 111 is not limited to being connected to the second flexible portion 112 by only one side (for example, two sides adjacent to the first flexible portion 111 are connected to the second flexible portion 112, and the other sides are suspended), and in the case where the second flexible portion 112 is fixed, the first flexible portion 111 may swing with respect to the second flexible portion 112 (or the first flexible portion 111 has a degree of freedom of movement with respect to the second flexible portion 112 and the reinforcing plate 15).
In this embodiment, the front area of the first flexible portion 111 may be smaller than the front area of the second flexible portion 112, and correspondingly, the back area of the first flexible portion 111 may be smaller than the back area of the second flexible portion 112. The back of the second flexible portion 112 is adhered and fixed on the surface of the reinforcing plate 15 facing the flexible circuit board 11 by the adhesive 16, so that the flexible circuit board 11 can be fixed on the reinforcing plate 15, the adhesive 15 is not arranged between the first flexible portion 111 and the reinforcing plate 15, the first flexible portion 111 can swing relatively to the second flexible portion 112 and the reinforcing plate 15, and the fixed area (i.e. the back of the second flexible portion 112) in the flexible circuit board 11 is larger than the swingable area (i.e. the back of the first flexible portion 111), so that the bonding reliability of the flexible circuit board 11 and the reinforcing plate 15 can be improved.
As shown in fig. 5, the flexible circuit board 11 may further include a strip-shaped third flexible portion 114, one end of the third flexible portion 114 is connected to the second flexible portion 112, and the other end of the third flexible portion 114 may be provided with a connector 17. In this embodiment, the strip-shaped third flexible portion 114 may be a flexible flat cable portion. External signals may be transmitted to the chip module 12 through the connector 17 and the flexible circuit board 11, or signals in the chip module 12 may be transmitted through the flexible circuit board 11 and the connector 17.
It should be noted that, the flexible circuit board 11 of the present embodiment is a monolithic circuit board, and for convenience of description, different areas of the flexible circuit board 11 are defined as a first flexible portion 111, a second flexible portion 112 and a third flexible portion 114. That is, in other embodiments, the flexible circuit board 11 may be divided in other ways, and the names of the divided different area definitions may be different.
As shown in fig. 4, a second contact pad 14 is disposed on a side of the chip module 12 facing the front surface of the first flexible portion 111, the second contact pad 14 is disposed opposite to the first contact pad 113, and the conductive adhesive 13 is disposed between the first flexible portion 111 and the chip module 12 and is electrically connected to the first contact pad 113 and the second contact pad 14, respectively.
Specifically, the conductive paste 13 may be composed of a resin matrix, conductive particles, dispersion additives, auxiliaries, and the like. The resin matrix may include epoxy resin, acrylate resin, polychloroethyl ester, and the like. The conductive particles may be gold, silver, copper, aluminum, zinc, iron, nickel powders and graphite, as well as some conductive compounds. The conductive adhesive 13 is easily contracted to generate internal stress after cold and hot impact.
The chip module 12 may be an LCOS chip. The chip module 12 may include a silicon substrate 121, a liquid crystal layer (not shown), and a glass cover plate 122, which are sequentially stacked. The glass cover plate 122 and the silicon substrate 121 may be stacked and staggered, and the second contact pad 14 is disposed at a staggered position of the glass cover plate 122 and the silicon substrate 121. The second contact pads 14 may be solder bumps provided on the chip module 12, in particular on the surface of the glass cover plate 122 facing the first flexible portion. The material of the solder bump may include lead-tin alloy, tin-silver alloy or tin-silver-copper alloy.
The glass cover plate 122 may be a conductive glass plate. The conductive glass plate may be formed by plating a conductive film, which may be, for example, an Indium Tin Oxide (ITO) thin film, on the surface of the insulating glass. Wherein the surface of the glass cover plate 122 provided with the conductive film may face the flexible circuit board 11.
A dam (not shown) may be further disposed between the silicon substrate 121 and the glass cover plate 122, and the dam may surround the liquid crystal layer to seal the liquid crystal layer between the silicon substrate 121 and the glass cover plate 122.
The surface of the silicon substrate 121 facing the glass cover plate 122 may be formed with a pixel array. In one embodiment, the silicon substrate 121 may be an Integrated Circuit (IC) drive chip electrically connected to individual pixels of the pixel array.
As shown in fig. 4, in this embodiment, the chip module 12 may be disposed directly above the flexible circuit board 11, and a lower surface of the chip module 12 may be attached to the front surface of the second flexible portion 112. Specifically, the lower surface of the silicon substrate 121 in the chip module may be attached to the front surface of the second flexible portion 112.
As shown in fig. 5, a plurality of third contact pads 116 may also be disposed on the second flexible portion 112. Referring to fig. 4 and 5, the silicon substrate 121 and the second flexible portion 112 may be electrically connected by a metal wire 18, and the metal wire 18 is connected to the third contact pad 116 and a corresponding conductive pad on the upper surface of the silicon substrate 121, respectively. In this embodiment, the metal wire 18 may be a gold wire. The silicon substrate 121 and the second flexible part 112 may be interconnected by a wire bonding process. In order to protect the metal wire 18 and improve the reliability of interconnection between the silicon substrate 121 and the second flexible portion 112, a protective paste may be further provided on the periphery of the metal wire 18.
Fig. 6 is a schematic diagram of a flexible printed circuit package structure after high-low temperature impact according to an embodiment of the invention. As shown in fig. 6, after the soft board packaging structure is subjected to high-low temperature impact, the conductive adhesive 13 is easy to shrink to generate internal stress, and since the adhesive 16 is not disposed between the first flexible portion 111 of the flexible circuit board 11 and the reinforcing plate 15, the first flexible portion 111 can absorb the internal stress of the conductive adhesive 13 through swinging (for example, slightly swinging upwards), which helps to protect the contact surface structure of the conductive adhesive 13 from being damaged by stress, so that the resistance value between the conductive adhesive 13 and the glass cover plate 122 is stable.
FIG. 7 is a schematic box-type diagram of a conventional LCOS package structure with resistance values after high-low temperature impact test. As shown in fig. 7, after a high-low temperature impact test (TC test) of 1500 cycles, the resistance value between the first contact pad on the first flexible portion (i.e., the conductive adhesive connection area) of the flexible circuit board and the glass cover plate increases to about 200 kohm. Fig. 8 is a schematic box-type diagram of a soft board package structure according to an embodiment of the invention after high-low temperature impact test. As shown in fig. 8, after the high-low temperature impact test with 1500 cycles, the resistance value between the first contact pad 113 on the first flexible portion 111 of the flexible circuit board 11 and the glass cover plate 122 is about 50Ohm (much smaller than 200K Ohm). Experimental results show that in the flexible board packaging structure of the present embodiment, the first flexible portion 111 of the flexible circuit board 11 can absorb the internal stress generated by the shrinkage of the conductive adhesive 13 through swinging, which is helpful to reduce the influence of the internal stress on the adhesive force of the conductive adhesive 13, and improve the stability of the resistance value between the conductive adhesive 13 and the glass cover 122.
In the flexible board packaging structure of this embodiment, the flexible circuit board 11 includes a first flexible portion 111 and a second flexible portion 112 that are connected to each other, a first contact pad 113 is disposed on a front surface of the first flexible portion 111, the reinforcing plate 15 is disposed on a back surface of the flexible circuit board 11 and is adhered to a back surface of the second flexible portion 112, a second contact pad 14 is disposed on a side of the chip module 12 facing the front surface of the first flexible portion 111, the second contact pad 14 is disposed opposite to the first contact pad 113, and the conductive adhesive 13 is disposed between the first flexible portion 111 and the chip module 12 and is electrically connected to the first contact pad 113 and the second contact pad 14 respectively. The flexible board packaging structure is easy to shrink after high and low temperature impact, so that internal stress is generated due to the fact that the reinforcing plate is bonded with the back surface of the second flexible portion but not bonded with the first flexible portion 111, that is, the first flexible portion 111 can swing relative to the second flexible portion 112 and the reinforcing plate 15, the internal stress can be released (absorbed) through the swing of the first flexible portion 111 of the flexible circuit board, the contact surface (for example, the contact surface of the conductive adhesive 13 and the second contact pad 14) structure of the conductive adhesive 13 is protected from being damaged by stress, the influence of the internal stress on the adhesive force of the conductive adhesive 13 is reduced, the stability of the resistance value between the first contact pad 113 and the second contact pad 14 is improved, and the reliability of the flexible board packaging structure is further improved.
Example two
The present embodiment provides an LCOS device, which includes the flexible printed circuit board package structure in the first embodiment, the flexible printed circuit board package structure includes a flexible circuit board 11, a reinforcing plate 15, a chip module 12 and a conductive adhesive 13, wherein the chip module 12 is an LCOS chip.
In the flexible circuit board packaging structure, the flexible circuit board 11 includes a first flexible portion 111 and a second flexible portion 112 that are connected to each other, a first contact pad 113 is disposed on a front surface of the first flexible portion 111, the reinforcing plate 15 is disposed on a back surface of the flexible circuit board 11 and is adhered to a back surface of the second flexible portion 112, a second contact pad 14 is disposed on a side of the chip module, facing the front surface of the first flexible portion, the second contact pad 14 is disposed opposite to the first contact pad 113, and the conductive adhesive 13 is disposed between the first flexible portion 111 and the chip module 12 and is electrically connected to the first contact pad 113 and the second contact pad 14 respectively.
The LCOS chip may include a silicon substrate 121, a liquid crystal layer (not shown in the figure), and a glass cover plate 122 that are sequentially stacked, where the glass cover plate 122 and the silicon substrate 121 are stacked and staggered, and the staggered portion of the glass cover plate 122 and the silicon substrate 121 may be provided with the second contact pad 14.
Because the flexible circuit board first flexible portion 111 and the reinforcing plate 15 are not bonded and are in a separable state in the flexible circuit board packaging structure, the internal stress generated by the conductive adhesive 13 after high-low temperature impact can be absorbed through the swing of the first flexible portion 111, which is helpful to protect the contact surface structure of the conductive adhesive 13 from being damaged by the internal stress, so that the resistance between the conductive adhesive 13 and the glass cover plate 122 is stable, the reliability of the flexible circuit board packaging structure can be improved, and the reliability of the LCOS device can be further improved.
The foregoing description is only illustrative of the preferred embodiments of the present invention, and is not intended to limit the scope of the claims, and any person skilled in the art may make any possible variations and modifications to the technical solution of the present invention using the method and technical content disclosed above without departing from the spirit and scope of the invention, so any simple modification, equivalent variation and modification made to the above embodiments according to the technical matter of the present invention fall within the scope of the technical solution of the present invention.