阅读说明：本技术 耐热脱模片和热压接方法 (Heat-resistant release sheet and thermocompression bonding method ) 是由 秋叶府统 于 2019-10-01 设计创作，主要内容包括：本申请的耐热脱模片是在利用热加压头进行压接对象物的热压接时配置在压接对象物与热加压头之间而用于防止压接对象物与热加压头的固着的片,其包含聚四氟乙烯(PTFE)或改性PTFE的片。其中,改性PTFE中的四氟乙烯(TFE)单元的含有率为99质量％以上。根据本申请的耐热脱模片,能够更可靠地应对缩短热压接所需的时间(操作时间)这一要求。(The heat-resistant release sheet of the present application is a sheet which is arranged between an object to be pressure-bonded and a heat pressing head when the object to be pressure-bonded is thermally pressure-bonded by the heat pressing head, and which is used for preventing the object to be pressure-bonded and the heat pressing head from being fixed to each other, and includes a sheet of Polytetrafluoroethylene (PTFE) or modified PTFE. The modified PTFE has a Tetrafluoroethylene (TFE) unit content of 99 mass% or more. According to the heat-resistant release sheet of the present application, it is possible to more reliably meet the demand for shortening the time (operation time) required for the thermal compression bonding.)

1. A heat-resistant release sheet which is arranged between an object to be pressure-bonded and a heat pressing head when the object to be pressure-bonded is thermally pressure-bonded by the heat pressing head, and which prevents the object to be pressure-bonded and the heat pressing head from being fixed to each other,

comprising a sheet of Polytetrafluoroethylene (PTFE) or modified PTFE,

wherein the modified PTFE has a content of Tetrafluoroethylene (TFE) units of 99 mass% or more.

2. The heat-resistant release sheet according to claim 1, wherein the heat of crystal melting of the PTFE or the modified PTFE, as evaluated by Differential Scanning Calorimetry (DSC) at a temperature rise rate of 10 ℃/min, is 25.0J/g or more.

3. The heat-resistant release sheet according to claim 1 or 2, which has a thickness of 1 to 50 μm.

4. The heat-resistant release sheet according to any one of claims 1 to 3, which has a tensile strength of 30.0MPa or more.

5. The heat-resistant release sheet according to any one of claims 1 to 4, which has a maximum tensile elongation of 380% or less.

6. A thermal compression bonding method for bonding an object by a thermal compression head, wherein,

performing thermocompression bonding of the object to be pressure-bonded by the heat pressing head in a state where the heat-resistant release sheet is arranged between the heat pressing head and the object to be pressure-bonded,

the heat-resistant release sheet according to any one of claims 1 to 5.

Technical Field

The present invention relates to a heat-resistant release sheet and a thermal compression bonding method using the same.

Background

Thermocompression bonding is used in the manufacture and flip chip mounting of semiconductor chips and the manufacture of Printed Circuit Boards (PCBs) using an underfill such as NCF (Non-Conductive Film) and NCP (Non-Conductive Paste). The thermocompression bonding method is also used for connection between a PCB and an electronic component using an Anisotropic Conductive Film (ACF). In thermocompression bonding of a bonding object, a thermal pressing head is generally used as a heat source and a pressure source. In order to prevent the fixation between the object to be pressure-bonded and the thermal pressing head during the thermal compression bonding, a heat-resistant release sheet is generally disposed between the object to be pressure-bonded and the thermal pressing head.

Patent document 1 does not disclose the heat-resistant release sheet itself, but discloses a polyimide film used by being disposed between an object to be pressure-bonded and a hot pressing head.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-91763

Disclosure of Invention

Problems to be solved by the invention

Polyimide is known as a resin excellent in heat resistance. By using a polyimide film for the heat-resistant release sheet, the thermocompression bonding temperature can be increased, and thus, the manufacturing efficiency and mounting efficiency of the semiconductor chip can be expected to be improved. However, in order to further improve the efficiency, it is necessary to shorten the time (work time) required for the thermocompression bonding. According to the study of the present inventors, it is clear that: when a polyimide film is used for a heat-resistant release sheet, it is difficult to sufficiently cope with reduction in the working time.

The purpose of the present invention is to provide a heat-resistant release sheet that can more reliably respond to a demand for shortening the operation time.

Means for solving the problems

The invention provides a heat-resistant release sheet which is arranged between an object to be pressure-bonded and a heat pressing head when the object to be pressure-bonded is thermally pressed by the heat pressing head and is used for preventing the object to be pressure-bonded and the heat pressing head from being fixed,

which comprises a sheet of polytetrafluoroethylene (hereinafter referred to as "PTFE") or modified PTFE.

The modified PTFE has a content of tetrafluoroethylene (hereinafter referred to as "TFE") units of 99 mass% or more.

From other aspects, the present invention provides a thermocompression bonding method,

the hot press bonding method of the object to be bonded by using a hot press head, wherein,

the heat-resistant release sheet is arranged between the heat pressing head and the object to be pressure-bonded, and the object to be pressure-bonded is subjected to thermocompression bonding by the heat pressing head,

the heat-resistant release sheet is the heat-resistant release sheet of the present invention.

ADVANTAGEOUS EFFECTS OF INVENTION

The PTFE sheet or modified PTFE sheet contained in the heat-resistant release sheet of the present invention has high heat resistance derived from PTFE or modified PTFE. Further, the PTFE sheet and the modified PTFE sheet have excellent thermal conductivity to an object to be pressure-bonded when thermocompression-bonded using a thermal pressing head, as compared with a polyimide film. Therefore, the heat-resistant release sheet according to the present invention can more reliably respond to a demand for shortening the operation time.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of the heat-resistant release sheet of the present invention.

Fig. 2 is a schematic view for explaining an example of a thermal compression bonding method using the heat-resistant release sheet of the present invention.

Fig. 3 is a schematic diagram for explaining a method of evaluating thermal conductivity of a pressure-bonding object when thermocompression bonding is performed using a thermal pressing head with respect to the heat-resistant release sheets of examples and comparative examples.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[ Heat-resistant Release sheet ]

Fig. 1 shows an example of the heat-resistant release sheet of the present invention. The heat-resistant release sheet 1 shown in fig. 1 is composed of a PTFE sheet 2. The heat-resistant release sheet 1 of fig. 1 has a single-layer structure of a PTFE sheet 2. The heat-resistant release sheet 1 has high heat resistance and releasability from PTFE contained in the sheet 2.

In an industrial thermocompression bonding process, a thermal pressure head is generally disposed in a transport path of an object to be bonded, and the object to be bonded transported in the transport path is sequentially thermocompressed. In this thermocompression bonding step, a strip-shaped heat-resistant release sheet may be fed between the thermal pressing head and the object to be bonded by conveyance. In this case, a new heat-resistant release sheet is generally supplied every 1 thermocompression bonding. In other words, the heat-resistant release sheet is heated from room temperature to the thermocompression bonding temperature at each thermocompression bonding, and necessary heat is transferred to the object to be bonded. Therefore, a slight difference in thermal conductivity of the heat-resistant release sheet greatly affects the operation time. Further, the influence becomes larger as the thermocompression bonding temperature rises. However, the heat-resistant release sheet 1 including the PTFE sheet 2 has excellent thermal conductivity to an object to be pressure-bonded when thermocompression-bonded using a thermal pressing head. Therefore, according to the heat-resistant release sheet 1, the requirement for shortening the operation time can be more reliably satisfied in addition to the increase in the thermocompression bonding temperature.

The PTFE contained in the PTFE sheet 2 preferably satisfies at least 1 property selected from the following properties (1) to (3), more preferably at least 2 properties, and still more preferably all the properties.

Characteristic (1): the heat of fusion of the crystal (hereinafter, abbreviated as "heat of fusion") evaluated by differential scanning calorimetry (hereinafter, referred to as "DSC") at a temperature increase rate of 10 ℃/min was 25.0J/g or more. The heat of fusion may be 27.0J/g or more, 28.0J/g or more, 29.0J/g or more, and further 30.0J/g or more. The upper limit of the heat of fusion is, for example, 82.0J/g or less, and may be 70.0J/g or less. When PTFE satisfies the property (1), the heat resistance of the heat-resistant release sheet 1 can be further improved while maintaining excellent thermal conductivity. The heat of melting of PTFE can be determined from the peak area of "endothermic peak by crystal melting of PTFE" measured when PTFE is heated at a predetermined temperature increase rate by DSC. The temperature of PTFE is increased from room temperature to 370 ℃ for evaluation of the heat of fusion. The PTFE contained in the PTFE sheet 2 is preferably PTFE subjected to sintering, and in this case, an endothermic peak due to crystal melting generally occurs in a temperature range of 250 to 340 ℃.

Characteristic (2): the crystallinity is 33.0% or more. The crystallinity may be 34.0% or more, 35.0% or more, and may be 36.0% or more. The upper limit of the crystallinity is, for example, 100.0% or less, and may be 85.4% or less. When PTFE satisfies the property (2), the heat resistance of the heat-resistant release sheet 1 can be further improved while maintaining excellent thermal conductivity. The crystallinity of PTFE can be determined by dividing the measured value of the heat of fusion by the theoretical value of the heat of fusion of the crystal possessed by the perfect crystal of PTFE. The PTFE contained in the PTFE sheet 2 is typically PTFE that has undergone sintering, and in this case, the theoretical value is 82.0J/g.

Characteristic (3): the peak temperature of the "endothermic peak by crystal melting of PTFE" (hereinafter referred to as "peak temperature") is 325.0 ℃ or higher. The peak temperature may be 326.0 ℃ or higher, and further 327.0 ℃ or higher. The upper limit of the peak temperature is, for example, 350.0 ℃ or lower. When PTFE satisfies the property (3), the heat resistance of the heat-resistant release sheet 1 can be further improved while maintaining excellent thermal conductivity.

The heat of fusion, crystallinity and peak temperature of PTFE vary depending on, for example, the molecular weight, molecular weight distribution, thermal history including sintering, and polymerization method and polymerization history of the PTFE.

The thickness of the PTFE sheet 2 is, for example, 1 to 50 μm, 5 to 40 μm, 10 to 35 μm, 20 to 35 μm, and further 25 to 35 μm.

The PTFE sheet 2 is preferably a sintered PTFE sheet comprising PTFE that has undergone sintering. In the present specification, the sintering of PTFE means that PTFE obtained by polymerization is heated to a temperature of not less than its melting point (327 ℃ C.), for example, 340 to 380 ℃.

The PTFE sheet 2 is preferably a non-porous layer. The PTFE sheet 2 may be an impermeable layer that does not allow a fluid (fluid) such as water to pass through in the thickness direction, because of the high liquid repellency (water repellency and oil repellency) of PTFE. The PTFE sheet 2 may be an insulating layer (non-conductive layer) because of the high insulating property of PTFE.

The PTFE sheet 2 is, for example, in the shape of a polygon including a square and a rectangle, a circle, an ellipse, and a tape. The corners of the polygon may have a curvature. The shape of the PTFE sheet 2 is not limited to these examples.

The PTFE sheet 2 may be a modified PTFE sheet. The modified PTFE sheet is represented by the above characteristics (1) to (3), and can have various characteristics mentioned in the description of the PTFE sheet 2 in any combination. The modified PTFE is a copolymer of TFE with a modifying comonomer. In order to be classified as modified PTFE, the TFE unit content in the copolymer must be 99 mass% or more. The modified PTFE is, for example, a copolymer of TFE with at least 1 modifying comonomer selected from ethylene, perfluoroalkyl vinyl ether and hexafluoropropylene.

The heat of fusion, crystallinity and peak temperature of the modified PTFE vary depending on, for example, the molecular weight, molecular weight distribution, thermal history including sintering, polymerization method and polymerization history of the modified PTFE, and the type and content of the structural unit as a component copolymerized with TFE unit.

The thickness of the heat-resistant release sheet 1 is, for example, 1 to 50 μm, and may be 5 to 40 μm, 10 to 35 μm, 20 to 35 μm, and further 25 to 35 μm.

The tensile strength of the heat-resistant release sheet 1 is, for example, 30.0MPa or more, and may be 33.0MPa or more, 34.0MPa or more, 36.0MPa or more, 40.0MPa or more, 45.0MPa or more, 50.0MPa or more, 55.0MPa or more, and further 60.0MPa or more. The upper limit of the tensile strength is, for example, 100MPa or less. According to the heat-resistant release sheet 1 having a tensile strength in these ranges, particularly the heat-resistant release sheet 1 having a tensile strength of 50.0MPa or more, the supply between the thermal pressing head and the object to be pressure-bonded by the conveyance can be performed more reliably and stably.

The maximum tensile elongation of the heat-resistant release sheet 1 is, for example, 380% or less, and may be 360% or less, 340% or less, 320% or less, 300% or less, 250% or less, 200% or less, 150% or less, and further may be 130% or less. The lower limit of the maximum tensile elongation is, for example, 30% or more. According to the heat-resistant release sheet 1 having the maximum tensile elongation in these ranges, particularly the heat-resistant release sheet 1 having the maximum tensile elongation of 150% or less, even when the heat-resistant release sheet 1 is fed between the heat pressing head and the object to be pressure-bonded by conveyance, when the heat pressing head and/or the object to be pressure-bonded and the heat-resistant release sheet 1 are locally bonded, the sheet 1 can be suppressed from following these members due to elongation. In other words, the releasability of the heat-resistant release sheet 1 from the hot pressing head and/or the object to be pressure-bonded can be further improved.

In the heat-resistant release sheet 1, another layer may be disposed on the main surface of the PTFE sheet 2. However, in order to more reliably meet the demand for shortening the operation time, it is preferable not to dispose another layer on the main surface of the PTFE sheet 2. That is, the heat-resistant release sheet 1 preferably has a single-layer structure of the PTFE sheet 2.

The shape of the heat-resistant release sheet 1 is, for example, a polygon including a square and a rectangle, a circle, an ellipse, and a belt. The corners of the polygon may have a curvature. The shape of the heat-resistant release sheet 1 is not limited to these examples. The polygonal, circular, and elliptical heat-resistant release sheet 1 can be distributed in a single piece, and the strip-shaped heat-resistant release sheet 1 can be distributed in a wound body (roll) formed by winding around a core. The width of the strip-shaped heat-resistant release sheet 1 and the width of a roll body formed by winding the strip-shaped heat-resistant release sheet 1 can be freely set.

[ method for producing Heat-resistant Release sheet ]

The heat-resistant release sheet 1 can be produced by, for example, the following method.

First, a PTFE powder (molding powder) is introduced into a mold, and the powder in the mold is preshaped by applying a predetermined pressure for a predetermined time. The preforming may be carried out at normal temperature. The shape of the internal space of the die is preferably cylindrical so as to enable cutting by a cutting machine described later. In this case, a columnar preform and a PTFE preform can be obtained. Next, the obtained preform was taken out of the mold and sintered at a temperature not lower than the melting point (327 ℃) of PTFE for a predetermined time to obtain a PTFE preform. Next, the obtained PTFE preform is cut to a predetermined thickness to obtain a PTFE sheet 2 as a cut sheet (cut sheet). The obtained PTFE sheet 2 may be used as it is as the heat-resistant release sheet 1, or may be used as the heat-resistant release sheet 1 after undergoing a predetermined treatment, lamination of other layers, or the like. When the PTFE preform is cylindrical, the PTFE sheet 2 and the heat-resistant release sheet 1 can be efficiently formed by a cutting machine that continuously cuts the surface while rotating the preform. Further, the thicknesses of the PTFE sheet 2 and the heat-resistant release sheet 1 to be formed can be relatively easily controlled by a cutting machine, and the PTFE sheet 2 and the heat-resistant release sheet 1 can be formed in a band shape. Further, by using a modified PTFE powder instead of a PTFE powder, a modified PTFE sheet can be formed by the above-described method.

The heat-resistant release sheet 1 can also be produced by the following method.

First, a substrate sheet to be coated with a PTFE dispersion liquid on the surface is prepared. The substrate sheet is composed of, for example, resin, metal, paper, and a composite material thereof. The surface of the substrate sheet to which the PTFE dispersion is applied may be subjected to a peeling treatment for facilitating the peeling of the PTFE sheet 2 from the substrate sheet. The peeling treatment may be performed by a known method. Next, a coating film of the PTFE dispersion was formed on the surface of the substrate sheet. Various known coaters can be used for coating the PTFE dispersion. The PTFE dispersion may be applied to the surface of the substrate sheet by immersing the substrate sheet in the PTFE dispersion. Next, a PTFE sheet is formed from the coating film of the PTFE dispersion formed on the surface of the substrate sheet by drying and sintering. Subsequently, the formed PTFE sheet was peeled from the base sheet to obtain a PTFE sheet 2 as a casting sheet. The obtained PTFE sheet 2 may be used as it is as the heat-resistant release sheet 1, or may be used as the heat-resistant release sheet 1 after being subjected to a predetermined treatment, lamination of other layers, or the like. In this method, the thicknesses of the formed PTFE sheet 2 and the heat-resistant release sheet 1 can be controlled according to the coating thickness and/or the number of times of coating of the PTFE dispersion to the substrate sheet. By using the modified PTFE dispersion instead of the PTFE dispersion, the modified PTFE sheet can be formed by the above-described method.

The PTFE sheet 2 may be stretched and/or rolled in order to increase the tensile strength of the heat-resistant release sheet 1 or suppress the maximum tensile elongation.

[ use of Heat-resistant Release sheet ]

As shown in fig. 2, the heat-resistant release sheet 1 can be used as a heat-resistant release sheet that is disposed between the hot pressing head 21 and the object 22 to be pressed when the object 22 to be pressed is thermocompressed by the hot pressing head 21, and prevents the fixation of both. The heat-resistant release sheet 1 is excellent in releasability. According to the heat-resistant release sheet 1, it is possible to prevent fixation (heat fixation) of the sheet 1 to the thermal pressing head 21 and/or the object 22 to be pressure-bonded, which is caused by heat at the time of thermocompression bonding.

The heat-resistant release sheet 1 can be fed and disposed between the heat pressing head 21 and the object 22 to be pressure-bonded by conveyance. The heat-resistant release sheet 1 supplied and arranged by conveyance is, for example, in a belt shape.

The object 22 to be pressure-bonded is, for example, a semiconductor chip, a PCB, or an electronic component. The heat-resistant release sheet 1 can be used for, for example, the manufacture and flip chip mounting of semiconductor chips by thermocompression bonding, the manufacture of PCBs, and the connection of electronic components, and the like.

[ Hot Press bonding method ]

The object 22 to be pressure-bonded can be subjected to thermocompression bonding using the heat-resistant release sheet 1 of the present invention. This thermocompression bonding method is a thermocompression bonding method for the object 22 to be bonded by the thermal pressing head 21, and the object 22 to be bonded is thermocompression bonded by the thermal pressing head 21 in a state where the heat-resistant release sheet 1 is arranged between the thermal pressing head 21 and the object 22 to be bonded. For example, the heat-resistant release sheet 1 can be supplied and disposed between the thermal pressing head 21 and the object 22 to be pressure-bonded by conveyance.

[ method for producing thermocompression bonded article ]

The heat-resistant release sheet 1 of the present invention can be used to produce a thermocompression bonded product. The manufacturing method of the thermal compression bonding object comprises the following steps: the heat-resistant release sheet 1 is arranged between the hot pressing head 21 and the object 22 to be pressure-bonded, and the object 22 to be pressure-bonded is subjected to thermocompression bonding using the hot pressing head 21, thereby obtaining a thermocompression bonded body of the object 22 to be pressure-bonded, that is, a thermocompression bonded body. Examples of thermocompression bonds are PCBs and electronic components.

Examples

The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

First, a method for evaluating the heat-resistant release sheet produced in this example is shown.

[ Heat of fusion, crystallinity and Peak temperature ]

The heat of fusion of the fluororesins (PTFE, modified PTFE, and PFA) constituting the heat-resistant release sheets of examples 1 to 6 having a single-layer structure of a PTFE sheet or a modified PTFE sheet and the heat-resistant release sheet of comparative example 1 having a single-layer structure of a tetrafluoroethylene-perfluoroalkoxyethylene copolymer (hereinafter referred to as "PFA") sheet were evaluated by the following methods.

A sample of 10mg of a fluororesin constituting the heat-resistant release sheet to be evaluated was collected. Subsequently, the collected sample was placed in a DSC apparatus (DSC 200F3, NETZSCH corporation) to obtain a DSC curve at which the temperature was raised from room temperature to 400 ℃ at a temperature raising rate of 10 ℃/min. The endothermic peak of the fluororesin occurring in the temperature range of 250 to 340 ℃ in the DSC curve obtained by the crystallization is analyzed to determine the peak temperature and the heat of fusion of the fluororesin. The respective crystallinities of PTFE, modified PTFE (examples 1 to 6) and PFA (comparative example 1) were determined by dividing the theoretical value of the heat of fusion of crystal of the sintered PTFE (82.0J/g) by the respective heat of fusion determined above.

[ tensile Strength and maximum tensile elongation ]

The tensile strength (tensile breaking strength) and the maximum tensile elongation were determined by a tensile test using a tensile tester (AG-I, Shimadzu corporation). The stretching direction is the longitudinal direction (MD direction) of the heat-resistant release sheet. The shape of the test piece was a dumbbell No. 1 as defined in JIS K6251: 1993. The measurement conditions were: the measurement temperature was 25 ℃, the distance between the standards of the test piece was 40mm, the distance between the jigs was 70mm, and the drawing speed was 200 mm/min. The maximum tensile elongation is calculated from the distance between the above-mentioned marks before the test and the distance between the marks at the time of breaking.

[ releasability at the time of thermocompression bonding ]

The mold release properties at the time of thermocompression bonding were evaluated as follows.

On a base of a thermocompression bonding apparatus (FC-3000W, product of dongli engineering corporation) having a thermal pressure head and a base, a semiconductor chip (7.3 mm × 7.3mm in size and 725 μm in thickness) was disposed as a pseudo pressure bonding object, and a heat-resistant release sheet as an evaluation object cut to 75mm × 75mm in size was further disposed on the semiconductor chip. The heat-resistant release sheet is disposed so that the semiconductor chip is located at the approximate center of the heat-resistant release sheet when viewed from a direction perpendicular to the disposition surface of the base. The set temperature of the susceptor was set to 120 ℃. Next, the thermal pressure head was lowered so that the pressure was 20N, and then the head was heated to 300 ℃ to perform a thermal compression bonding test for 10 seconds, to evaluate whether or not the thermal fixing of the heat-resistant release sheet to the thermal pressure head or the semiconductor chip as the object to be bonded occurred. The heat-resistant release sheet after the thermocompression bonding test was judged to have good releasability (o) when peeled from the thermal press head or the semiconductor chip naturally or by pulling the sheet with a hand, and was judged to have failed to peel when peeled without pulling the sheet with a hand (x).

[ thermal conductivity at the time of thermocompression bonding ]

The thermal conductivity at the time of thermocompression bonding was evaluated as follows. A specific evaluation method will be described with reference to fig. 3.

Assuming a pseudo flip chip mounting, a silicon base 52 (thickness: 360 μm), an adhesive sheet 53 (EM-350 ZT-P, thickness: 60 μm) assumed to be NCF, and a semiconductor chip 54 (size: 7.3 mm. times.7.3 mm, thickness: 725 μm) were disposed in this order on a base 51 of a thermocompression bonding apparatus (FC-3000W, manufactured by Toray engineering Co., Ltd.) including a thermal head 57 and the base 51. A thermocouple 55 for measuring the maximum reaching temperature of the adhesive sheet 53 in the thermocompression bonding test is embedded in the adhesive sheet 53. The thermocouple 55 is disposed such that a measuring portion at the tip thereof is located substantially at the center of the adhesive sheet 53 when viewed in a direction perpendicular to the disposition surface of the susceptor 51. Next, a heat-resistant release sheet 56 cut to 150mm × 150mm in size as an evaluation target was disposed on the semiconductor chip 54. The heat-resistant release sheet 56 is disposed so that the semiconductor chip 54 is positioned at the substantially center of the heat-resistant release sheet 56 when viewed from the direction perpendicular to the disposition surface of the base 51. The set temperature of the susceptor 51 was set to 120 ℃. Next, the thermal pressure head 57 was lowered so that the pressure was 20N, and then the head was heated to 280 ℃ to perform a thermal compression test for 10 seconds, and the maximum reaching temperature of the adhesive sheet 53 at the time of the test was measured by the thermocouple 55. The thermal conductivity of the heat-resistant release sheet when thermocompression bonding was performed using a hot press head was evaluated from the measured maximum reached temperature.

[ Heat resistance ]

The heat resistance was evaluated by pressing the tip of a soldering iron set to 280 ℃, 290 ℃ or 300 ℃. Specifically, the tip of the iron set to each temperature was pressed against the surface of the heat-resistant release sheet to be evaluated for 10 seconds, and a case where the surface of the heat-resistant release sheet was not melted by the heat of the iron was judged as good in heat resistance (o), and a case where the surface was melted was judged as failed in heat resistance (x).

(example 1)

PTFE powder (Polyflon PTFE M-18 manufactured by Daikin Industries, Ltd.) was introduced into a cylindrical mold and preformed at a temperature of 23 ℃ and a pressure of 8.5MPa for a pressure application time of 1 hour. Subsequently, the preform thus formed was taken out of the mold and sintered at 370 ℃ for 24 hours to obtain a cylindrical PTFE preform having a height of 300mm and an outer diameter of 470 mm. Next, the obtained PTFE preform was cut by a cutting machine to produce a PTFE sheet having a thickness of 30 μm, which was used as the heat-resistant release sheet of example 1.

(example 2)

A modified PTFE sheet having a thickness of 30 μ M was produced in the same manner as in example 1 except that a modified PTFE powder (Dyneon TFM modified PTFE TFM1700 manufactured by 3M, having a TFE unit content of 99 mass% or more) was used in place of the PTFE powder, and this was used as the heat-resistant release sheet of example 2.

(example 3)

A fluorine-based surfactant (CF) was added in an amount of 0.67 wt% based on the solid content of PTFE to a commercially available PTFE dispersion (Fluon AD911E manufactured by Asahi glass Co., Ltd.)₃(CF₂)₇CH₂CH₂-(OCH₂CH₂)_mOH: m-3 to 5), a PTFE dispersion for forming a coating film on a substrate sheet is prepared. Subsequently, a tape-shaped Aluminum foil (60 μm thick, manufactured by Mitsubishi Aluminum) as a substrate sheet was immersed in the PTFE dispersion prepared above and pulled upward, thereby forming a coating film of the PTFE dispersion on the surface of the substrate sheet. Next, the substrate sheet was heated in a heating furnace set to 100 ℃ to dry the coating film, and then further heated in a heating furnace set to 380 ℃ to sinter the dried film. The impregnation of the substrate sheet in the PTFE dispersion, and the drying and sintering after the impregnation were continuously carried out while roll-conveying the substrate sheet at a speed of 0.7 m/min. Subsequently, the impregnation into the above-mentioned PTFE dispersion, and the subsequent drying and sintering were repeated again to form a PTFE sheet having a thickness of 30 μm on the base sheet. Next, the formed PTFE sheet was peeled from the base sheet to obtain a heat-resistant release sheet of example 3.

(example 4)

The PTFE preform produced in example 1 was cut by a cutting machine to obtain a PTFE cut film having a thickness of 50 μm. Next, the obtained cut film was rolled by a roll rolling device equipped with a pair of metal rolls maintained at 170 ℃, to prepare a PTFE sheet having a thickness of 30 μm, which was used as the heat-resistant release sheet of example 4.

(example 5)

The heat-resistant release sheet of example 5 was obtained in the same manner as in example 3, except that the thickness of the PTFE sheet formed on the base sheet was set to 5 μm, and the PTFE sheet was peeled from the base sheet to prepare a heat-resistant release sheet.

(example 6)

The heat-resistant release sheet of example 6 was obtained in the same manner as in example 3, except that the thickness of the PTFE sheet formed on the base sheet was set to 10 μm, and the PTFE sheet was peeled from the base sheet to prepare a heat-resistant release sheet.

Comparative example 1

A PFA sheet (NEOFLON PFA AF-0025 manufactured by Daikin Industries, Inc., having a perfluoroalkoxyethylene unit content of 1 mass% or more) having a thickness of 25 μm was prepared as the heat-resistant release sheet of comparative example 1.

Comparative example 2

A polyimide sheet (KAPTON 100H, manufactured by Dupont-Toray) having a thickness of 25 μm was prepared as the heat-resistant release sheet of comparative example 2.

The evaluation results of the properties of the heat-resistant release sheets of examples and comparative examples are shown in table 1 below. The thermal conductivity (maximum reaching temperature) of comparative example 1 could not be measured because the heat-resistant release sheet melted.

[ Table 1]

In the respective tables, "-" means undetermined.

Industrial applicability

The heat-resistant release sheet of the present invention can be disposed between a thermal pressing head and an object to be pressure-bonded when the object to be pressure-bonded is thermally pressed by the thermal pressing head, and can be used for preventing the fixation of the thermal pressing head and the object to be pressure-bonded. Thermocompression bonding using the heat-resistant release sheet of the present invention can be applied to, for example, manufacturing of semiconductor chips, flip chip mounting, manufacturing of PCBs, and connection of electronic components.