MACHINE OF PASTE SHRINKAGE AND EXPANSION IN Z DIRECTION

The disclosed provides a machine of paste shrinkage and expansion for timely monitoring a paste shrinkage in a Z direction during a UV curing process and for obtaining a change rate of a paste in a Z direction after a certain process. The machine comprises: a bottom substrate; a top substrate which is transparent and configured to be placed on the paste so that the paste is sandwiched between a top surface of the bottom substrate and a bottom surface of the top substrate, wherein the top surface of the bottom substrate and the bottom surface of the top substrate are provided with first and second reflecting layers, respectively, and define a thickness of the paste; a platform for supporting the bottom substrate; a plurality of pressing clamps configured for securing the bottom substrate on the platform in the Z direction; a plurality of pushing clamps configured for securing the bottom substrate in radial and circumferential directions; a plurality of UV sources positioned uniformly around the paste; and a sensor configured for measuring the thickness of the paste. The bottom substrate and the platform comprise a substrate dial and a platform dial, respectively, and the bottom substrate has a profile consistent with the platform dial. The disclosed provides methods for timely monitoring a paste shrinkage in a Z direction during a UV curing process and for obtaining a change rate of a paste in a Z direction after a certain process.

TECHNICAL FIELD

The disclosure relates to a machine of paste shrinkage and expansion in a Z direction. In particular, using the machine, the paste can be UV cured and a paste shrinkage in the Z direction during the UV curing process can be timely monitored, and a change rate of the paste in the Z direction can be obtained after a certain process which can be the UV curing process, a thermal curing process or a reliability test process. A method for timely monitoring the paste shrinkage in the Z direction during the UV curing process and a method for obtaining the change rate of the paste in the Z direction after the certain process are also provided.

BACKGROUND ART

Adhesives are widely used in many technical fields. For example, an active alignment (AA) adhesive can be used in AA process in compact camera modules (CCM) and Optical module film. Shrinkage and expansion of the adhesive substantially affect a lens of the CCM, and therefore it is important to know rules of the shrinkage and expansion of the adhesive during curing process.

In general, a volume and linear shrinkage of plastic materials, unsaturated polyester and epoxy resin can be measured by standard ISO 352, and measuring the volume and linear shrinkage is a good way to find out the rules of the shrinkage and expansion of the adhesive. However, this method cannot be totally aligned with real applications regarding the shrinkage and expansion in a Z direction for some factors, for example, due to resin out-gas during thermal curing process, especial for UV curable adhesive paste. Semicircle groove method is used by ASTM D2566-79 standard, which can't be applied to UV curable adhesive paste due to heterogeneous curing and the change of resin coefficient of thermal expansion for state change. The heterogeneous curing issue is then be solved using a cylinder method. However, a heterogeneous cavity is generated for cylinder method, which affects the accuracy of data. Meanwhile, many companies use a machine of 3D Dimensional Laser Confocal and a Vernier Caliper to measure a dimension of the paste before and after curing, but the accuracy will be affected by noise at a measuring position for each measurement.

It is desired to solve the problems as above.

SUMMARY OF THE INVENTION

An object of the disclosure is to solve one or more of the above problems.

The object is achieved by a machine of paste shrinkage and expansion for timely monitoring a paste shrinkage in a Z direction during a UV curing process in claim1, a method for timely monitoring a paste shrinkage in a Z direction during a UV curing process using the machine of paste shrinkage and expansion in claim11, a machine of paste shrinkage and expansion for obtaining a change rate of a paste in a Z direction after a certain process in claim15, and a method for obtaining a change rate of a paste in a Z direction after a certain process using the machine of paste shrinkage and expansion in claim16.

With the machine and the method described in the disclosure, the paste shrinkage over UV applied time in the Z direction during the UV curing process can be timely monitored, which facilitates to analyze the shrinkage trend or the presence of the shrinkage delay during the UV curing process. This also provides a great significance to understand, control or fully make use of the curing kinetic of UV curing. Further, the paste's UV response performance for difference compositions can be detected using the machine and the method described above.

In addition, the change rates of the paste in the Z direction after the UV curing process, the thermal curing process and the reliability test process can be obtained. For an adhesive used in a camera, this helps to simulate a focal length change of the camera after AA process and reliability test.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout the drawings, like reference numerals refer to like components throughout this specification. This specification does not describe all components of the embodiments, and general information in the technical field to which the present disclosure belongs or overlapping information between the embodiments will not be described.

It will be understood that the terms “includes”, “comprises”, “including” and “comprising” when used in this specification specify the presence of a stated component, but do not preclude the presence or addition of one or more other components. Also, it is to be understood that the singular forms “a” “an” and “the” include plural referents unless otherwise stated. A component which is described or shown as being a unitary component may be implemented as including a plurality of components and an assembly or portion which is described or shown as including a plurality of components may be implemented as a unitary component unless the context clearly dictates otherwise.

In general, the disclosure relates to a machine of paste shrinkage and expansion in a Z direction, and the machine can provide two functions. The paste can be cured by a UV light in this machine and a first one of the functions is to monitor a paste shrinkage in the Z direction over UV applied time during this UV curing process, and a second one of the functions is to facilitate to obtain a change rate of the paste in the Z direction after a certain process.

In particular, in this specification, the paste is a kind of adhesive or adhesive sample in a form of paste, and may be referred to as “adhesive paste” for convenience. The term “certain process” can be any process the paste may be subjected to during which the paste may shrink or expand due to some special composition(s) contained in the paste. For example, the certain process may be the UV curing process mentioned above during which the paste will be cured using the UV light due to a UV curing agent contained in the paste, the certain process may be a thermal curing process during which the paste will be cured, in a thermal oven for example, due to a thermal curing agent contained in the paste, or the certain process may be a reliability test process during which the paste will be put into a box of high temperature and high humidity (HTHH). In an example to be described, the thermal curing process is carried out after the UV curing process and the reliability test process is carried out after UV curing and the thermal curing process. However, this is not necessary and the three processes can be carried out independently or in any combination.

The paste may shrink or expand depending on actual compositions contained the paste. For example, three kinds of adhesive pastes used in the example to be described in this specification shrink during the UV and thermal curing processes and expand during the reliability test process. To identify the degree of shrinkage or expansion of the paste after the certain process, a term “change rate” is used in the specification which means a shrinkage rate if the paste shrinks or an expansion rate if the paste expands. In the machine, the paste is dispensed in an annular pattern on a bottom substrate of the machine which is substantially arranged in a horizontal plane, the Z direction is perpendicular to the plane and to the bottom substrate, and the change rate of the paste in the Z direction means the degree of the change of a thickness of the paste in the Z direction. The thickness of the adhesive paste can also be referred to as a bonding line thickness in related technical fields and is denoted by a reference sign B in the specification.

In general, the change rate R of the paste in the Z direction after the certain process is calculated out based on an initial thickness value of the paste in the Z direction before the certain process, Bini, and a final thickness value of the paste after the certain process, Bfin, using the formula I: R=(Bini−Bfin)/Bini. The thickness values Biniand Bfincan be the thickness values measured at one and the same point of the paste before and after the certain process. However, in order to improve the precision, the thickness values Biniand Bfincan be averaged thickness values based on many thickness values measured at a set of points (preferably, one and the same set of points) in a circumferential direction of the pattern of the paste before and after the certain process, respectively. This can be achieved using the machine and method to be described in this specification.

The disclosure will be described in detail with reference to the drawings.FIGS.1-6illustrate a machine of paste shrinkage and expansion in a Z direction constructed according to the principle of the disclosure, in whichFIG.1is an overall view of the machine andFIGS.2-6each are enlarged views illustrating a portion of the machine inFIG.1.

The machine of paste shrinkage and expansion in the Z direction can be placed on a table10or similar component, and comprises a rotatable platform110which can be mounted on the table10. A drive mechanism (not shown) is provided for the platform110and configured for driving and rotating the platform110. The drive mechanism can be any well-known drive mechanism in the art and, for example, includes a motor and a reducer, only a wire12is illustratively shown inFIGS.1-4.

On the platform110, a bottom substrate210is positioned and the paste to be monitored or measured is dispensed on it (FIGS.2-5), and a top substrate220will be moved onto the paste from a storage position P, as shown inFIG.6, by a pick-up element310. In operation, the paste is dispensed or attached on the bottom substrate210firstly, the bottom substrate210is then be placed on the platform110, and eventually the top substrate220is placed on the paste to cover it. Stubs120(FIG.5) extending from the platform110are provided to support the bottom substrate210directly so that the bottom substrate210can be leveled in a horizontal direction by adjusting the stubs120. Three supporting stubs120are provided between the platform110and the bottom substrate210. Preferably, the stubs120can be made from an elastic material in order to minimize vibration caused to the bottom substrate210by the rotating platform110. In this way, the paste can be sandwiched between a top surface212of the bottom substrate210and a bottom surface222of the top substrate220, as shown inFIG.7. First and second reflecting layers are applied to the top surface212of the bottom substrate210and the bottom surface222of the top substrate220, respectively, functions of which will be described in the following. The top substrates220, or preferably both the bottom and top substrates210,220, can be made from any suitable material through which a laser light can be transmitted and, in an example each of the bottom and top substrates210,220can be provided as a glass sheet.

As shown inFIGS.8a-8c, the bottom substrate210and the platform110are provided with a substrate dial214and a platform dial114, respectively, and the substrate dial214and the platform dial114function as alignment features of the bottom substrate210and the platform110. The bottom substrate210has a profile which is consistent with the platform dial114of the platform110, so that the bottom substrate210can be precisely re-positioned in the same initial position on the platform110by placing it within the platform dial114, as shown inFIG.8c, after it has been removed from the platform110for other operations, for example for curing the paste in other places. The substrate dial214and the platform dial114have initially aligned lines, so that the bottom substrate210can be precisely re-positioned in the same orientation relative to the platform110after it has been removed from the platform110. As an example, the initially aligned lines can be a 0° line in the substrate dial214and a 0° line in the platform dial114, or a 90° line in the substrate dial214and a 90° line in the platform dial114, or maybe a 270° line in the substrate dial214and a 270° line in the platform dial114, as is indicated by a reference sign245inFIG.8c.

Back toFIG.1-5, a plurality of pushing clamps410and a plurality of pressing clamps420are provided for securing the bottom substrate210relative to the platform110in radial and circumferential directions and in the Z direction, respectively. Both the pushing clamps410and the pressing clamps420can extend from or be attached to the platform110.

With reference toFIG.5, the pushing clamps410are movable so that the bottom substrate210can be removed and replaced on the platform110, and each of the pushing clamps410comprises a base portion412extending from the platform110and an abutting portion414which is configured for abutting an outer circumferential surface of the bottom substrate210in a substantial horizontal direction. The abutting portion414can be movable relative to the base portion412in the horizontal plane, for example, in the radial direction. Each of the pressing clamps420can comprise a base portion422extending from the platform110and a pressing finger424pivotable relative to the base portion422about a pivoting shaft425so that the bottom substrate210can be pressed and therefore secured on the platform110in the Z direction. In the embodiment, three pushing clamps410and three pressing clamps420are provided, but it should be understood that the number and the detail structure of the pushing clamps410and the pressing clamps420are not limited to those shown in the drawings.

An “alignment combination” of the alignment features with the pushing clamps410and the pressing clamps420ensures that, the bottom substrate210, or a “paste holding combination” including the bottom substrate210, the top substrate220and the paste therebetween, after being removed from the platform110, can be precisely re-positioned on the platform110at the same initial position and orientation, ensuring a high consistency and precision during multiple measurement operations. For the thermal curing process and the reliability test process during which the paste holding combination needs to be moved from the platform to another place and returned onto the platform later, the provision of the alignment combination ensures that the bottom substrate has a consistent position relative to the platform.

On opposite sides of the platform110, two rails510and520and four UV sources, for example UV lamps in the embodiment, are arranged, with two UV lamps530on the rail510and two UV lamps540on the rail520, as shown inFIGS.1-3. All the UV lamps should be arranged uniformly around the paste so that the paste can be cured evenly and the thickness of the paste can reduce evenly. In the embodiment as shown, one of the rails,520, as well as the two UV lamps540, is configured to be movable or removable, so that the bottom substrate210can be taken away. Alternatively, according to actual condition, it may be provided that only one or more UV lamp is movable along the corresponding rail or removable, or maybe two rails510and520are movable or removable, as long as the bottom substrate210or the paste holding combination can be removed as desired.

As described above, the top substrate220can be moved on the paste from a storage position P by the pick-up element310. With reference toFIG.6, one end310aof the pick-up arm310is fixed to a supporting base320which in turn is fixed on the table10, and the other end310bof the pick-up arm310is provided with a suction disk330for picking up the top substrate220. A numerical control unit (referred to as “NCU” hereinafter)340is configured for controlling operations of the pick-up arm310and can be provided at the supporting base320or some other location convenient to operate. The pick-up element310operates to pick up the top substrate220at the storage position P (FIG.6), move it onto the paste on the bottom substrate210, and optionally apply a downward force on the top substrate220to press the paste to a predetermined initial thickness value.

A sensor610is provided and attached to a post620which in turn is fixed to the table10, and thus the sensor610is fixed relative to the table10, as shown inFIG.4. The sensor610can be a laser displacement sensor and is configured for measuring a thickness of paste at a certain point using optical principle. The thickness B of the paste can be understood as a distance from the bottom surface222of the top substrate220to the top surface212of the bottom surface210, as shown inFIG.7.

The principle how sensor610measures the thickness of the paste is illustrated inFIG.7, in which the top substrate220, the bottom substrate210, an incident light L1with the incident angle α, and reflected lights L2and L3reflected by the first reflecting layer at the bottom surface222of the top substrate220and the second reflecting layer at top surface212of the bottom substrate210are shown. The incident light L1is emitted out from a light emitting element of the sensor610onto the top substrate210and transmitted through the top substrate210, a portion of the incident light L1being reflected by the first reflecting layer at the bottom surface222of top substrate220, as indicated by the first reflected light L2, and others of the incident light L1being projected onto the top surface212of the bottom substrate210without travelling through the paste and reflected by the second reflecting layer, as indicated by the second reflected lamp L3. Preferably, the top substrate210has a thickness which is small enough so that the two reflected lights L2and L3have substantially parallel reflecting directions, as shown inFIG.7. A horizontal distance H is obtained firstly based on the reflected lamps L2and L3received by the light receiving element, and then the thickness B of the paste can be calculated out geometrically.

According to the disclosure, the top substrate220is constructed, configured or specially treated so that a laser light from the sensor610is allowed to be transmitted through. In an embodiment, the top substrate220and the bottom substrate210have a profile accuracy of less than ¼λ. In an embodiment, the top substrate220or both the top and bottom substrate are transparent glass sheets or glass sheets with a suitable coating.

In an embodiment, the top substrate220is further designed so that a UV light can be transmitted through, and the UV light emitted out from the UV lamps530and540are projected angledly onto a top surface of the top substrate220and then transmitted through the top substrate220into the paste to cure it. In an alternative embodiment, depending on the position of the UV lamps530and540, the top substrate220can be further designed so that a UV light cannot be transmitted through, and the UV light emitted out from the UV lamps530and540are projected onto the paste between the top substrate220and the bottom substrate210from side.

With the machine described above, a method for timely monitoring the paste shrinkage in the Z direction over UV applied time during the UV curing process includes, as shown in a flow chart inFIG.9, a step910, assembling and leveling the platform110on the table10; a step920, placing the bottom substrate210on the platform110with the platform dial114and leveling the bottom substrate210to be within a predetermined tolerance by adjusting the stubs120; a step930, securing the bottom substrate210on the platform using the pushing clamps410and the pressing clamps420; a step940, dispensing the paste of an adhesive sample on the bottom substrate210in an annular pattern, as shown inFIG.8c; a step950, picking up and moving the top substrate220from its storage position P onto the paste using the pick-up element310; a step960, triggering the UV lamps to cure the paste, while triggering the sensor610; and a step970, measuring the thickness of the paste at one point over UV applied time at predetermined time intervals while recording the thickness values.

In some embodiments, the method may further include recording the initial thickness value before step960. Alternatively, the method may further include applying a downward force on the top substrate220by the pick-up element310to press the paste to the initial thickness value and record the initial thickness value before step960. Still alternatively, the method may include, before step960, rotating the platform110and measuring the thickness values at a preset number of points of the paste in a circumferential direction of the paste by repeating measurement operations at the predetermined time intervals and averaging the recorded thickness values to obtain an averaged thickness value as the initial thickness value and recording the initial thickness value.

The method may further include a step of making a sketch using the thickness values recorded during the curing process after the UV curing process finishes, which can reflect the thickness reduction rule of the paste over the UV applied time.

In some embodiments, the method may further include rotating the platform110and measuring the thickness values at the preset number of points of the paste in the circumferential direction by repeating measurement operations at the predetermined time intervals and averaging the recorded thickness values to obtain an averaged thickness value as the final thickness value, after the step970.

Preferably, the method may further include a step of calculating the change rate, i.e. the shrink rate, of the paste after the UV curing process based on the initial thickness value in step950, as Bini, and the final thickness value, Bfin, using the formula I.

As described above, the change rate of the paste in the Z direction after any process can be obtained based on the initial thickness value before the process, Bini, and the final thickness value after the process, Bfin, using the formula I, and, for precision consideration, it is preferable that the thickness values Biniand Binibe averaged thickness values based on many thickness values measured at one and the same set of points in the circumferential direction of the pattern of the paste before and after the certain process, respectively.

For the UV curing process, as described above, before the UV curing process and after the process finishes, the thickness values Biniand Binican be obtained by rotating the platform110and measuring the thickness values at one and the same set of points in the circumferential direction and averaging the measured thickness values at these points. However, the thickness values Binican be the predetermined thickness value which is achieved by the NCU and the pick-up element310minstead of the averaged thickness values before the UV curing process.

A method for obtaining a change rate of a paste after a certain process includes: a preparation step1010in which the machine and the paste are ready for operation, a step1020in which the thickness values Biniis obtained by rotating the platform110and measuring the thickness values at a set of points in the circumferential direction of the paste and averaging the measured thickness values at these points; a step1030in which the certain process is carried out to the paste; and a step1040in which, after the certain process finishes, the thickness values Bfinis obtained by rotating the platform110and measuring the thickness values at the same set of points in the circumferential direction of the paste and averaging the measured thickness values at these points; and a step1050in which the change rate is calculated out based on the thickness values Biniand Bfinusing the formula I.

The preparation step1010may include: the step910, assembling and leveling the platform110on the table10; the step920, dispensing the paste of an adhesive sample on the bottom substrate210in an annular pattern; the step930, placing the bottom substrate210on the platform110within the platform dial114and leveling the bottom substrate210to be within a predetermined tolerance by adjusting the stubs120; the step940, securing the bottom substrate210on the platform110using the pushing clamps410and the pressing clamps420; the step950, picking up and moving the top substrate220from its storage position P onto the paste using the pick-up element310.

For the thermal curing process and the reliability test process in which the paste needs to be moved to other places, the step1030may include: a step1032in which the pick-up element310is moved away and one or more UV lamp and/or one or more rail are removed so that the paste holding combination can be removed from the platform110; a step1034in which the process is carried out to the paste; and a step1036in which the paste holding combination is returned back to the machine and the bottom substrate210is secured to the platform110at the initial position and orientation, using the alignment features, the pushing clamps410and the pressing clamps420.

Although the machine and the methods of using the machine have been described in detail as above, some examples are given for further explanation so that the technical effects and advantages can be better understood.

Three kinds of adhesive pastes A, N and D which are widely used in active alignment process in CCM are used in this example for comparison purpose. They are dispensed on the bottom substrate210in the same annular pattern as shown inFIGS.8c-8d, with the same weight of 4.4 mg for control. The paste pattern has the same initial thickness of 150 μm which is achieved by using the pick-up element310to press the top surface220under the control of the NCU.

First of all, three pastes are subjected to the UV curing process in the machine, wherein the UV curing depths for the three pastes are 450 μm, 490 μm and 200 μm, respectively, and the UV applied time is 2 Sec, 2 Sec and 4 Sec, respectively, under UV intensiveness of 1500 mw/cm2.

The thickness values are measured and collected using the sensor610every 20 mSec. All the measured thickness values are plotted into sketches, as shown inFIGS.11a-cfor the three adhesives. It shows from the sketches that, for all the three adhesives, once the UV lamps and the sensor610are triggered the thickness value starts to decline over UV applied time, which means the UV curing agents contained in the adhesives are triggered when the pastes are exposed to the UV light and start to reaction. After the reaction of the UV curing agent completes, the thickness curves tend to be stable. By comparison, the adhesives A and N inFIGS.11aandbhave a faster UV response than D inFIG.11d, and therefore it takes a longer time to cure the adhesive D before the thickness B becomes stable, 4 mSec. The object of timely monitoring the paste shrinkage in the Z direction is achieved.

Based on the initial thickness value of 150 μm, as Bini, and the thickness value when the thickness curves are stable, as Bfin, the change rate, i.e. the shrinkage rate, of the pastes can be calculated out using the formula I, as shown inFIG.11d.FIG.11dshows that N has a higher UV change rate than A and D. Therefore, the object of obtaining the change rate of the paste in the Z direction is also achieved.

Alternatively, for precision purpose as described above, the thickness value Bfincan be the averaged thickness values by rotating the platform110and measuring the thickness value at a set of points of the paste in the circumferential direction after the UV curing process. For example, by controlling the time interval at which the sensor610measures the thickness value as well as a rotation speed of the platform, 18 or 20 or any other number of points can be measured.

The three pastes are then subjected to the thermal curing process, and the obtained thickness value Bfinafter the UV curing process will be the used as Biniin the thermal curing process. Then, according to the method inFIG.10, the pick-up element310is removed and the paste holding combination is moved to the thermal oven to carry out the thermal curing process to the paste. Each of the three adhesive pastes A, N and D is cured at 80° C. for 1 hour. Once the thermal curing process completes, the paste holding combination is returned back to the machine according to the step1036. The steps1040and1050are performed in which the thickness values Bfinis determined and the change rate is calculated out using the formula I, please refer to theFIG.12. FromFIG.12, it can be known that, the thickness of the paste further declines during the thermal curing process, and the adhesives N and A have a higher shrinkage rate than the D adhesive.

All the steps regarding the thermal curing process are repeated for the reliability test process except the paste holding combination is moved to the box of high temperature and high humidity (HTHH) instead of the thermal oven and the humility and temperature condition during the HTHH process is different from the thermal curing condition during the thermal curing process. The pastes stay in the HTHH box with atmospheric of 85° C. & 85 rh % for 120 hrs. All the pastes absorb moisture and expand and the change rates for the three pastes after this process are shown inFIG.13. The sketch inFIG.13shows that adhesive A has a higher expansion rate than adhesives D and N. It should be noted that, for the HTHH process, the change rate obtained by the formula I will be negative because the pastes expand during this process. It is easily understood that when the result of the formula I is negative, the change rate will be expansion rate andFIG.13shows the absolute values of the results.

In this example, with the machine and the method described in the disclosure, the paste shrinkage over UV applied time during the UV curing process in the Z direction can be timely monitored, which facilitates to analyze the shrinkage trend or the presence of the shrinkage delay during the UV curing process. In addition, this provides a great significance to understand, control or fully make use of the curing kinetic of UV curing. Resin out-gas and other factors which affect the results as listed in the background have no influence on the results with this method, and the accuracy can be ensued with the rotatable platform.

In this example, with the machine and the method described as above, the change rates of the paste in the Z direction after the UV curing process, the thermal curing process and the reliability test process are obtained. For an adhesive used in a camera, this helps to simulate a focal length change of the camera after AA process and reliability test.

In this example, two types of adhesives A and L which contain different types of resins are used, and only the UV curing process is carried out to them. During this process, the thickness values are measured by the sensor610every 20 Sec and recorded accordingly, and the recorded thickness values are plotted as shown inFIGS.14aand14b. By comparison, it can be known that, after the UV lamps of the machine are triggered, the thickness values of the adhesive A paste decreases immediately while the thickness of the adhesive L paste substantially has no change within 8 Sec and then starts to decline, which illustrates that adhesive L has a UV delay which may be due to the inclusion of some special composition, for example, cationic epoxy curing agent.

Therefore, in addition to timely monitor the paste shrinkage in the Z direction during the UV curing process, the paste's UV response performance for difference compositions, for example, the type or performance of the UV curing agent contained in the adhesive, can be identified or determined using the machine and the method described above.