DE4038989A1 - Tension-free bonding of flat workpiece to substrate - with different coefft. of thermal expansion using cationically hardening resin compsn. which is irradiated then heated to moderate temp. - Google Patents

Abstract

Bonding a workpiece (I) to a substrate (II) comprises (1) applying thin layer of reaction resin (III) on bonding zone by means of application appts.; (2) activating (III) with UV or visible light from radiation source; (3) bringing together (I) and (II), and opt. orienting precisely if necessary within the open or "shuffle" time; (4) bringing bonding zone during initial hardening time of less than 1 minute to elevated temp.; (5) opt. effecting other bondings of other (I) to initial hardening on the (II), then (6) hardening completely. (III) is UV-initiated cationically hardening resin with joint open time 1 second to 30 minutes, initial and complete chemical hardening of which can be carried out at 40-100 deg.C. USE/ADVANTAGE - Bonding flat, tension-sensitive (I) to (II), partic. in automated processes, where high positional accuracy and short cycle times are required. One component, storage stable (in dark) (III) can be used, bonds obtd. resist temp. changes and contact with solvent

Description

The invention relates to a method for producing a span low-adhesion bonding and a adhesive bond made with it binding.

Technical adhesives are often only for a very specific one Suitable for use. Because in particular the context between the chemical structure of an adhesive or one material to be glued and the strength and properties so far only partially recognized the adhesive connection an adhesive is limited in each case optimized business spectrum. A sophisticated technical Adhesion problem therefore generally requires a special one Adhesive.

Requirements for an adhesive do not only result from the Properties of an adhesive bond that can be produced with it, but increasingly also from the processing properties, e.g. B. in terms of safe and fast processing in a highly automated process. In joining processes, the one require a high degree of positioning accuracy, must by Achieving a certain strength of the adhesive connection be fixed. To avoid excessively long machine belts times for one for precise, precise bonding it is necessary from high part, if a secure basic strength after a short time Curing time is reached.

In the case of thermally curable adhesives, curing can take place through an increase in temperature, with UV-curable by inten more intense radiation can be accelerated. The disadvantage is first case, the one required for quick hardening, mostly relatively high temperature. The second case requires one of  sufficient outside irradiation, d. H. Kle not unshaded order. While a high hardening temperature causes damage of the parts to be glued, as it cools down after hardening there is tension, for many Bonding a conventional radiation curing because of abge shaded glue points not feasible. In addition, the Heating an adhesive connection within the adjustment device the positioning accuracy is usually insufficient.

For a special glue problem, namely the quick and chip Low-stress bonding of flat workpieces with a difference expansion coefficient, no one has yet been used suitable adhesive process found, which further conditions conditions for the physical and chemical stability of the generated ten adhesive connection fulfilled.

The object of the present invention is therefore a Verkle exercise procedure including the associated adhesive formulation for Specify above problem, which is a high positioning accuracy with short cycle times in an automated remote control process allowed. Furthermore, the bond with a one-component storage-stable reaction resin take place during the strength of the adhesive connection even after changing the temperature seln and in contact with solvents should.

According to the invention, this object is achieved by a method for low-tension bonding of a flat workpiece with a base, the workpiece and base being different have coefficients of thermal expansion,

• - in which a reaction resin by means of an application device device applied in a thin layer to an adhesive point becomes,
• - Akti by a radiation source with UV or visible light fourth,  
• - Workpiece and base together with their glue points inserts and if necessary according to a template within a precise open joint time,
• - The glue point for fixation during a hardening time of less than 1 minute an elevated temperature is brought
• - If necessary, further gluing of further workpieces be carried out on the base until hardening and finally be fully cured with a UV-initiated cationically curing reaction resin an open joint time in the range of one second to 30 minutes is selected, the chemical hardening and hardening at 40 can be carried out up to 100 ° C.

Further refinements of the invention and one derived therefrom adjustable adhesive connection can be found in the subclaims men.

In the process according to the invention, a UV-activatable reak tion resin used. A photoinitiator contained in the resin breaks down into cations during irradiation, which affects the hardening process catalyze. After activation by irradiation with UV or visible light, the hardening process proceeds automatically continues and is only in the hardening speed by affects the temperature.

A particular advantage of such reactive resins is that it is are one-component systems that are almost in the dark are storable for as long as desired. That with two and more components necessary systems immediately before application mixing together is not necessary.

The application itself is problem-free, because that before activation inert reaction resin, no special equipment required  different. Such are necessary for reactive resins, for example Resin residues are regularly cleaned within the pot life must be and therefore only short machine run times possible do. The remaining resin must then be a special waste acts and is disposed of.

In the present process, the reaction is as thin as possible resin layer applied to an adhesive, which is attached Workpiece or pad can be. There are various Suitable methods that have a correspondingly thin adhesive or can produce reaction resin layer, for example Stamping, spreading, printing or applying over a perforated plate dispenser. Draw the thin layer of adhesive net compared to a thicker because of its overall better Heat dissipation.

After activating the adhesive layer, the hardening starts reaction. Given at room temperature or another Temperature is now an open joint time available, after which changes the reaction resin into a hardened state. The positioning of the Workpiece on the base and a possibly necessary slipping or correcting the position. The open time for joining can be selected or selected by a variation set a suitable reaction resin. It will be sufficient long chosen to ensure safe processing or precise posi guaranteeing the workpiece and is at the same time sufficiently short to harden as quickly as possible achieve.

The hardening itself is carried out after positioning briefly heating the component. This can be done by Heating the entire assembly (workpiece plus pad) or by local heating in the area of the glue joint for example by a heating stamp. Off selected reactive resins require only a relatively small amount for hardening moderate temperature increase to approx. 40 to 100 ° C. This is ins  especially for flat and sensitive workpieces from Vor partly because with the temperature difference between hardening tempera ture and normal temperature (or operating temperature of a Component containing adhesive connection) which differ by mechanical coefficients of thermal expansion Tension of the adhesive connection increases. A completely tension-free Condition exists only in the area of the curing temperature. The The method according to the invention therefore produces a relatively span low-adhesion bonding. The minimization of tensions will also supported by the selection of flexible adhesives.

After hardening, the adhesive connection is fixed. Further Bonding can take place in parallel or in succession subsequently carried out with individual hardening will. With a sufficiently long joint opening time it is also possible to use several glue points in one process step to provide a reaction resin layer, this together activate the positioning, fixation and hardening of the individual adhesive connections, however, individually and through local heating of individual glue points. Here high position accuracy of the glued workpieces with short cycle times of the bonding process or the equipment used for this purpose. This has little As a result, machine occupancy times only require a simple ches equipment and allows a safe implementation. Is too a joint hardening of several glue points in one Possible step.

After all the adhesive connections have hardened, they are removed hardened. For this purpose, the arrangement produced by gluing in an oven to a temperature corresponding to the hardening temperature brought and left there for some time. Usually are less than two hours to fully cure sufficient. With various reactive resins, it is already sufficient the conditions or hardening times selected for hardening in order to to achieve a complete hardening of the adhesive connection, so that subsequent curing is not necessary because  it no longer leads to any improvement in the adhesive connection.

The method is particularly advantageous for flat work pieces used that are sensitive to be hardened by induced tensions can react. Particularly thin surfaces Workpieces show a bimetal with high clamping effect caused by the different thermal expansion glued or connected parts to bend the Workpiece leads. The method according to the invention avoids these effects and is therefore suitable for workpieces that Bracing or bending with break or other change the properties react, especially workpieces sensitive materials such as ceramics, semiconductor devices or other sensitive precision components, micromechanical or other finely structured components. It will be maximum Deflection from 2 µm to 1 cm glued workpiece length expansion coefficients differing by a factor of 10 glued materials measured.

In an advantageous embodiment of the invention, reak tion resins used, which have a joint opening time between 1 Se customer and 2 minutes. With such a short joining time The hardening time is usually reduced. At 60 to 100 ° C harden such reactive resins within a few seconds the one.

The process can be implemented with a reaction resin, which hardens after a UV-initiated cationic process. Such reactive resins are from the group of epoxy resins chosen, with up to 50 percent by weight of other compounds can be contained with epoxy resins under the given Curing conditions show copolymerization. these are in particular polyhydroxy compounds and / or electron-rich compounds containing vinyl groups. Cyclic ethers can also be included. While as the base resin one or more resins from the group of cycloaliphatic and aliphatic Epoxy resins are selected, usually low molecular weight  and are low viscous, to achieve one for the ver drive suitable consistency advantageously a solid Resin offered for copolymerization, for example a Cresol novolak epoxy resin. As an aliphatic epoxy resin epoxidized soybean oil preferred.

The photoinitiator is in the process according to the invention used reaction resin in a proportion of 0.1 to 5 Ge percent by weight included. Suitable photoinitiators for the UV initiated cationic curing mechanisms are exemplary Wisely derived from stable organic cations, in particular those with sulfur or iodine as the central atom. As special before Aromatic onium salts with complex types have been found to be particularly useful ions proven. A photoinitia containing a Lewis acid gate can be realized as a Pi donor transition metal complex the. Phenacylsulfonium salts, hydro xylphenylsulfonium salts and sulfoxonium salts. Organi too cal silicon compounds used in property when exposed to UV radiation release a silanol from aluminum alcoholates, init cationic hardening.

The reaction resin may also contain conventional additives be like adhesion promoters, flow aids, photosensitizers lisators, coinitiators or thixotropic agents, esp special fillers.

For a special embodiment in which the reaction resin layer using a method similar to screen printing a perforated plate dispenser is applied, in particular highly disperse silicas are suitable as fillers.

In one embodiment, the adhesion promoter is used for ver gluing a workpiece with a silicon one Glue point on an aluminum or plastic base Epoxysilane and an acrylic resin used as a leveling agent.

All can usually be used as photosensitizers  ten and known compounds are used, for example wise perylene.

The selection of a suitable radiation source for initiation of the curing process is from the selected photoinitiator or depending on the system photoinitiator / photosensitizer. It is primarily based on the sensitivity range ches of the photoinitiator in such a way that as large a part as possible of the emitted radiation spectrum of the radiation source within this sensitivity range lies. The intensity of the If possible, the radiation source is chosen so that at Irradiation of a reaction resin layer the contained therein Photoinitiator full in the shortest possible time is constantly being implemented. The radiation duration is still there on the layer thickness of the reaction resin layer and on the Absorption depending on the components contained therein. sales The photoinitiator is said to be complete, however Avoid exposure to radiation for too long to avoid excessive exposure Heating of the reaction resin and a triggered to prevent premature hardening.

Mercury vapor is well suited as a radiation source lamps that are optimal in the following examples Irradiation times for thin reactive resin layers in the area result in fewer seconds.

As a special application of the method according to the invention in the following the production in one embodiment a spray module for inkjet printers described, therefor particularly suitable reaction resin compositions specified and the properties of the ver bonding with those of known adhesives or adhesive drive compared.

In addition, the process is explained by the associated two figures, which the Verkle Practice a spray head (workpiece) on an aluminum support (Document).  

There is a specific problem for the application mentioned in a sprayer built on a silicon substrate head with the approximate dimensions 10 mm x 10 mm x 2 mm with its silicon underside flat on an aluminum carrier stick on.

Ink channels end in on a narrow side of the spray head for example 40 µm diameter nozzles. Because of this ge Structural dimensions are the printing properties of the later injection module significantly from a low-tension Ver Adhesion of the spray head on the aluminum carrier depends. Even small ver occurring when the bond hardens tensions lead to a deterioration in print quality, especially in multi-color printing. There are different for colors used different spray modules that the Image composed of several colors exactly one above the other need to print to get high quality.

In addition, the bond can be in contact with the inks used stand so that it must also be resistant to the ink. Even when stored in ink for a long time, it must not pass through Washout-related weight loss is another through on show excessive mass increase due to sources. In doing so also a low glass transition temperature in the range of Room temperature and sufficient mechanical strength the adhesive connection remains guaranteed.

The reaction resins used as adhesives are by Zu administration of thixotropic agents to a specific application tion device optimized.

Application devices suitable for the method according to the invention are, in particular, so-called perforated-plate dispensers, for which an adjustment of the reaction resin viscosity to 12 (± 4) Pas at a shear rate of 40 s ^-1 (plate-cone viscometer) is required. Other devices or processes are screen printing (20 ± 5 Pas, 40 s ^-1 ), stamp transfer (3 ± 1 Pas) or perforated-floor dispenser (70 ± 10 Pas 20 s ^-1 ).

The resins are prepared by dissolving the solid components (here cresol novolak epoxy resin) in the liquid components at 90 ° C with the exclusion of light. Then who dissolved the photoinitiators and other additives with stirring at about 50 ° C. The aerosils are dispersed in with a toothed disc rotating at 3000 min ^-1 (approx. 4 cm diameter). At approx. 100 Pa, degassing takes place for 15 minutes.

Fig. 1: For the application of the reactive resins onto the adhesive surface of the aluminum support 1 is used a Lochplattendispenser, which is applied to 1 cm ² area of 2.5 mg reactive resin in 247 points 2. This requires a thixotropic adjustment of the adhesive.

With an intensive mercury vapor lamp (here: Blue-Point, company Hönle), the optimal radiation conditions are determined, whereby a radiation duration of 5 seconds at a distance of 15 mm has proven itself for the selected lamp. After the radiation (see arrows 3 ), the reaction resin has a jointing time of approx. 15 minutes at room temperature, within which the workpiece to be bonded must be positioned.

Fig. 2: Now the spray head 4 (workpiece) is placed on the provided and provided with the reaction resin layer on the aluminum substrate 1 (= base) and pressed, whereby a continuous reaction resin layer 5 with a thickness of about 17 microns is formed .

By attaching a heating stamp to the aluminum support this in the area of the glue point for approx. 20 seconds at 65 ° warmed up. This causes the reaction resin to gel and fix it Spray head on the carrier. The fixation is sufficient to before the final hardening further processing steps and in particular to make further bonds without one Fear of slipping of the spray head.  

The final and complete curing of the reaction resin is carried out by heating at 80 ° C for two hours.

The fully bonded spray modules are tension-dependent te deflection investigated, to loosen the adhesive connection necessary shear forces determined and the measurement after a position Spray module in ink (21 days / 70 ° C) repeated. In addition, the change in mass of the hardened adhesive bond examined after the ink storage mentioned.

Mixtures are used for the reactive resins common individual components are composed. For the Base resin becomes a low viscosity cycloaliphatic epoxy resin (CY 179, Ciba-Geigy), a solid cresol novolak EP resin (Quatrex 3310, Dow Chemical) and an epoxidized soybean oil (Edenöl D 82, Henkel) selected. Cyclopentadienyl isopro pylbenzene iron (II) hexafluorophosphate (Irgacure 261, Ciba Geigy) is used as a photoinitiator and as a sensi sator perylene (Merck).

The adhesive is thixotroped with highly disperse silica ren (Aerosil 200 and Aerosil R 805, Degussa).

An epoxysilane (A 187, UCC) and as Leveling agent an acrylic resin (Modaflow, Monsanto) used.

The composition specially selected for this application suitable reaction resins can be found in Table 1 below take (specified in parts by mass).

The reaction resin mixtures are thixotropic Fluorescent green-yellow fluorescent. Relevant own Some compositions are listed in Table 2 lists.

Table 2

The specified viscosities are determined at the start of the measurement telt, the shear forces occurring in the plate-cone viscometer So not yet dismantled.

Another investigation of the manufactured according to the invention Adhesive connection was used to determine the temperature changes consistency. For this purpose, several were invented Spray modules glued according to the invention alternately to -25 ° C cool, kept at low temperature for 15 minutes, then heated to + 70 ° C for 15 minutes and then turned off again chilled. The bonds according to the invention also show 30 such temperature cycles no failures.  

Some of the shear forces required to shear the spray heads Adhesive connections can be found in Table 3. Another Determination of the shear forces is carried out after the 21 day Ink storage is done at 70 ° C and is also table 3 can be seen.

Table 3

The injection modules with han standard adhesives according to the manufacturer's instructions glued and subjected to the same tests. It resulted for both the process and the properties the adhesive connection significant disadvantages compared to the invention. These showed either too high reactivity and therefore too low open joint time, insufficient temperature cycle strength , viscosities not suitable for processing or after bonding too high tension in the injection module, the this led to bending up to 10 µm. With the Be none of the known showed moods of ink resistance tested adhesives a satisfactory result. Watched were above all an impermissibly high mass increase due to Auf swell, an excessive decrease in mass due to leaching and / or one that has dropped to an impermissibly low value Shear strength of the adhesive connection.

LX-B 22 hardens from the specified adhesive compositions fastest and therefore has the shortest open joint time on. This is due to the relatively high proportion of cycloaliphati schematic epoxy (CY 179). The mixture with the slowest hardening is LX-B 31, due to the relative  high proportion of Novolak resin (Quatrex 3310). So for a suitable mixture with individu Select the hardness behavior.

The example of the composition LX-B 31 shows the dependency the reaction resin properties from the curing conditions Radiation dose, curing temperature and time determined.

Fig. 3 shows the strength of an adhesive bond as a function of time, the various curves A to F were determined under different conditions.

In the test execution corresponding to the short E and F. the reaction resin was UV-irradiated for 10 s at room temperature and put the adhesive joint together. For hardening is on Heated to 70 ° C. The are at constant intervals Forces required to shear off the workpiece (in Newtons) Right. It can be seen that a 10 N sufficient here curing under these conditions reached after 70 to 75 s becomes.

The measurement curves C and D were ge with an adhesive connection measure, the gluing point of which is irradiated for 60 s at room temperature and finally kept at 70 ° C. It is clear observed faster hardening. The hardening (reached at 10 N shear force) is reached after 37 to 45 s.

Finally, curves A and B show that among the listed the highest curing speed with the highest temperature of 90 ° C is reached, although in this Trial was irradiated only 10 s.

Fig. 4 shows the viscosity behavior of the 50 s irradiated adhesive LX-B 31 shows over time depending on the temperature. At room temperature, no increase in viscosity is observed in the measuring interval (line G). In contrast, at 70 ° C (see curve H) the viscosity rises steeply after approx. 30 s.

The adhesive is already above 50 Pas or after 75 s cured so far that the viscosity no longer with the plate-cone viscometer used for the measurement leaves. So it is sufficient at room temperature long open joint time available, whereas at temperature rapid hardening and hardening takes place.

The inventive method is characterized by its simple and safe execution, can at low tempe repairs are carried out, leads to low tension and runs sufficient strong adhesive connections, which also both against over fluctuating temperature loads as well are extremely insensitive to ink storage. The Process and the adhesive bond produced by it especially for tension sensitive flat workpieces with different thermal expansion coefficient ge is suitable. Advantageous general applications are there too see where a solvent resistance of the adhesive bond is required. In addition, with the fiction process, of course, also made bonds which are not so demanding. The application explained in the exemplary embodiment for a Spray module is therefore only particularly advantageous and the To see breadth of the invention, not restrictive embodiment.

Claims (7)

1. Method for the low-stress bonding of a flat workpiece to a base, the workpiece and base having different thermal expansion coefficients,

• - in which a reaction resin is applied by means of an application device in a thin layer to an adhesive point,
• - is activated by a radiation source with UV or visible light,
• - the workpiece and the base are joined together with their gluing points and, if necessary, precisely aligned within a joint opening time,
• - The adhesive point for fixation is brought to an elevated temperature during a hardening time of less than one minute,
• - If necessary, further bonding of further workpieces until hardening is carried out on the base and finally completely hardened, a UV-initiated, cationically hardening reaction resin with an open joint time in the range from one second to 30 minutes being selected, its chemical hardening and hardening can be carried out at 40 to 100 ° C.

2. The method according to claim 1, characterized records that a reaction resin with an open joint time from 1 second to 2 minutes is used. 3. The method according to claim 1 or 2, characterized ge indicates that the hardening at 60 to 90 ° C. is carried out within a few seconds.   4. The method according to any one of claims 1 to 3, characterized in that a reaction resin is used containing
50 to 99 percent by weight of an epoxy resin or a mixture of several epoxy resins,
1 to 50 percent by weight of a compound capable of copolymerization with the epoxy resin, selected from polyhydroxy compound and / or a compound containing vinyl groups,
0.1 to 5 weight percent of a cation-producing photo initiator
as well as, where appropriate, other additives customary for reactive resins, such as adhesion promoters, flow control agents, thixotropic agents, in particular fillers, or sensitizers. 5. The method according to any one of claims 1 to 4, characterized characterized in that a reaction resin is used which is cycloaliphatic epoxies, aliphatic epoxies and as a compound capable of copolymerization, a cresol novo contains resin. 6. The method according to at least one of claims 1 to 5, characterized in that in the reak Resin as photoinitiators derived from ferrocene salts, Sulfonium salts or in the presence of organoaluminum Silicon compounds decomposing under UV to silanols be used. 7. Adhesive connection between a flat workpiece a first coefficient of thermal expansion, in particular re made of a semiconductor material or metal, and one made of Me tall or plastic underlay with a second, from the first different coefficient of thermal expansion, where the adhesive connection consists of a reaction resin,  which after a cationic hardening process at moderate Temperatures of less than 100 ° C hardened and therefore span low glass transition temperature is less than or equal to 40 ° C has and wherein the adhesive connection of the workpiece and / or Substrate at least partially against one used for curing Radiation is shadowed.