JP6133879B2 - Method and apparatus for sealing an electronic component using a volume reducing material that causes phase change - Google Patents

Description

  The present invention relates to a method for sealing an electronic component mounted on a carrier, in which A) a processing step of placing the electronic component for sealing in a mold cavity connected to the carrier, and B) a mold A processing step of filling the cavity with a liquid sealing material; and C) a processing step of at least partially curing the sealing material in the mold cavity. The invention also relates to an apparatus for carrying out such a method.

  In the sealing of electronic components, more specifically, in the sealing of semiconductors mounted on a carrier (for example, a lead frame), different types of sealing processes, among others, pressure molding, pressure molding, injection molding, Alternatively, a combination of these sealing processes can be used. It should be noted here that semiconductors are broadly interpreted so that in addition to the chip, they also include other electronic components such as, for example, light emitting diodes (LEDs). The carrier with the electronic components is now clamped between the moldings so that the mold cavity is defined around the sealing component. The liquid encapsulant is fed into these mold cavities after at least partial curing when the molded part is released and the carrier with the encapsulated electronic part is removed. The encapsulant typically consists of a thermosetting epoxy or resin that includes a filler. Pressure is applied to the sealing material that is also normally heated, and as a result, the sealing material that is not already liquid is heated until it becomes liquid. The liquid encapsulant fills the mold cavity (which is normally heated) and the liquid encapsulant is at least partially cured within the mold cavity, for example, by chemical bonding (crosslinking). In order to improve the sealing quality, a predetermined pressurization (that is, a gas pressure lower than the atmospheric pressure) can be applied before the supply of the sealing material is started. The mold cavity is now pressurized through a suction channel (vent) that can discharge gas during filling of the mold cavity. It is very important to completely fill the mold cavity with the encapsulant. The problem with sealing electronic components is that, depending on the specific conditions, the mold cavity is not always completely filled with the sealing material, so that an opening (void) remains in the seal to be created. Sometimes it ends up. This phenomenon occurs in particular in front of the encapsulant flow front in the mold cavity, where (small) bubbles or emitted gases can be encapsulated in the encapsulant.

  The present invention provides a method and apparatus for encapsulating electronic components and has the object of reducing the possibility of voids occurring within the encapsulation of electronic components.

The present invention provides for this purpose a method of the kind mentioned in the preamble, in which the volume reducing material is used before the mold cavity is completely or partially filled with the encapsulant. Introduced into the volume reducing material causes a phase change such that the volume of the volume reducing material decreases while filling the mold cavity with the sealant . Here, the volume reducing material can at least condense from the gas phase while filling the mold cavity with the encapsulant, but the volume reducing material can also be transferred from the gas phase to the solid phase or volume. It is also possible for the depletion material to condense as vapor (optionally superheated) or be transferred to a solid. To perform the method, the volume reducing material may be actively carried into the mold cavity in the gas phase and / or as a mist, and in a more specific option, the volume reducing material is activated as superheated steam. To supply. On the other hand, the volume reducing material can be in the liquid or solid phase when actively transported into the mold cavity. Relevant is that under conditions prior to supplying the encapsulant to the mold cavity, the volume reducing material has a relatively large volume (low mass density), and under conditions where the encapsulating process takes place, The volume reducing material is to cause a phase change. Relevant here is not only the temperature, but the pressure increase is also a demanding part, since the temperature at which the phase change occurs depends greatly on the pressure. Sealing takes place in a temperature range of [150-200] ° C. and a pressure of [50-100] Bar, more particularly [60-90] Bar. In order to obtain the maximum reduction in the volume of the volume reducing material (ie the maximum compression factor), it is further desirable that the molecular weight of the volume reducing material be as small as possible.

The present invention also provides a film material, is disposed between the mold cavity to be connected to the carrier and the carrier with electronic components, liquid sealant is supplied between the bearing member and the film material, the volume The reducing material provides a way to be transported between the film and the mold cavity. Therefore, the volume reducing material is separated from the electronic component for sealing, from the carrier, and from the sealing material. To the extent that the presence of a (relatively small amount) volume reducing material can impair the sealing process, these drawbacks can be prevented. The volume-reducing material is thus ultimately located on one side of the opposing film material spaced away from the carrier with the electronic components, while the carrier with the electronic components is sealed (during the later sealing process). On the contrary, it is located on the opposite side of the film (ie on the side of the film material facing the carrier with the electronic components).

Regardless of this state (ie, whether or not it has been reduced), the volume-reducing material therefore does not affect the conditions of the carrier with the electronic component and the encapsulant, and in conclusion contact is avoided. The advantage of sealing electronic components where the film material is applied in combination with the application of a volume reducing material is the advantage of applying the sealing material (eg, no opportunity for adhesion of the sealing material to the mold cavity) Therefore, it can be achieved without the structural measures to be taken to allow the mold cavity to be vented. In sealing with the film material, therefore, there is no need to take measures to prevent an excessive pressure increase in the mold cavity. Especially in advanced mold cavities (optical lenses applied in combination with LEDs, eg fully or partially encapsulated and / or manufactured), the overpressure can be greatly increased, thereby The risk of damaging the film material increases. For this purpose, the discharge channel is usually arranged in a molding part in which the mold cavity (or mold cavities) is arranged. The presence of volume reduction material, so that one or more of the mold cavity venting (vent) is unnecessary, as a result of a phase change in the volume reduction material, for volume reduction occurs, waste such measures End up. This makes a molded part with one or more mold cavities not only easy to manufacture, but perhaps more importantly a simpler molded part that is less susceptible to malfunctions during operation. This is because the degassing measures connected to the mold cavity are easily clogged by dirt, or, for example, film separation does not function properly with the sealant. Cleaning such molded parts with clogging degassing measures can be labor intensive and can hinder production. Another advantage of excessive degassing measures is that it allows the application of a smooth, even polished mold cavity to produce a seal with certain potential uses. The present invention eliminates the need to guide the filled gas to the vent through the surface roughness of the mold cavity. Accordingly, for example, a lens can be manufactured using a sealing material.

Yet another highly desirable volume reducing material property is that a decreasing phase change still does not occur before the pressure increases, for example, premature condensation of the volume reducing material is prevented thereby. is there. This means that the desired effect (substantial volume reduction of the volume reducing material during the sealing process) does not occur, for example, in the case of premature condensation, and condensation may prevent good sealing. Not only important because there is no. On the other hand, the phase change of the volume reducing material before starting the sealing process, however, is allowed in the case of an expanding phase change. The volume reducing material is introduced into the mold cavity, for example, in the liquid or solid phase, but this is not a problem if the volume reducing material expands before the actual sealing process takes place. The reason is that due to evaporation of the liquid or solid before the start of the sealing process, the volume reducing material is then increased in volume (i.e. having a very low mass density Δ before the sealing process is started) Is). The volume reduction of the volume reducing material can be quite substantial due to condensation. This volume reduction thus leaves the possibility of a small amount of (small) bubbles being encapsulated in the encapsulant, thereby making the enclosing compartment smaller enough to no longer qualify as an enclosing area. Due to this effect, the encapsulant completely fills the encapsulated area despite the initial encapsulation. According to the prior art, air or other gas that was present in the mold cavity during the supply of the sealant is of course compressed as a result of the increased pressure, but this compression factor is equal to the (gas) pressure. It is directly proportional to the increase. The encapsulated compressed gas thus forms a void within the encapsulant that is particularly undesirable. This will be described below based on specific embodiments. The presence of a volume reducing material that causes a phase change can achieve improved quality, especially in the case of electronic products that are relatively difficult to fully encapsulate. Here, for example, larger products, flip chips, and other laminated electronic components can be envisaged in which there are intermediate regions that are difficult for the encapsulant to flow. Application of a small amount of liquid encapsulant and good filling over the surface of the (larger) mold cavity can likewise be achieved using the method according to the invention.

An advantageous choice can be found by selecting H ₂ O (water) as the volume reducing material . Not only is the volume-reducing material low in molecular weight (M _water = 0.018 kg / mol) but also has a desired condensation behavior from 1 to, for example, at a pressure increase of 80 bar (eg at a constant temperature of T = 150 ° C.). doing. From the gas phase at 1 atm with ^{_{Δ water = ± 0.5kg / m 3}} , Δ water = by changes to the liquid phase with ± 900 kg / m ³ is produced, with volume reduction is therefore approximately 1800 Order It occurs with a coefficient. Conventionally, there has always been a starting point in the prior art where the sealing process is interrupted by water. For this purpose, the encapsulant is therefore adjusted with great care according to the prior art. Due to the unexpected and unclear insight leading to the present invention, on the other hand, the presence of water in the sealing device can lead to improved encapsulation results. Another option for a volume reducing material that condenses under sealing conditions is C ₂ H ₅ OH (ethanol), M _ethanol = 0.046 kg / mol. Increasing pressure results in a volume decrease by a factor on the order of about 350. This is still a significant volume reduction that can also lead to a clear improvement in encapsulation results.

A further improvement of the desired effect is to pressurize the mold cavity before or during the filling of the mold cavity with the encapsulant as in process step B). This refers to pressurization relative to atmospheric pressure, that is, pressure less than 1 atmosphere. The pressurization that can be achieved in the mold cavity in a simple manner reaches an absolute value of 0.1 Bar. The volume reduction as calculated in the previous paragraph is thereby increased by a factor of 10. This is due to a change in liquid phase with Δ _water = ± 900 kg / m ³ , under a modified starting condition of Δ _water = ± 0.5 kg / m ³ , thereby a factor of the order of about 18,000. This means that a volume reduction occurs. For ethanol, this results in a volume reduction factor on the order of about 3,500. Therefore, a very favorable effect is improved by pressurizing the mold cavity. In addition, it is also possible to pressurize the mold cavity during or before introducing the volume reducing material into the mold cavity in order to remove more of the gas present (generally air). The removal of the gas initially present in the mold cavity can be achieved by cleaning the mold cavity with a gaseous volume reducing material , or optionally supplying (injecting) a volume reducing material in a superheated vapor state. It is also possible. After pressurizing the mold cavity and cleaning the mold cavity, it is also desirable to pressurize the mold cavity again as described above.

The volume reducing material can be added to the mold cavity separately from the encapsulant, for example, by spraying or spraying the volume reducing material , but a small amount of liquid (eg, liquid water) or solid particle volume reducing material (ice ) (Rapid evaporation) can also lead to the desired starting condition of the mold cavity prior to actual sealing. However, the volume reducing material can be supplied in combination with the encapsulant, and the volume reducing material can enter the mold cavity before the encapsulant. The encapsulant may be adjusted for this by, for example, adding a volume reducing material to the encapsulant.

Once the mold cavity is positioned relative to the electronic component for sealing during processing step A), the sealing material may be supplied to the mold cavity. It is also possible to heat the encapsulant prior to displacing the encapsulant into the mold cavity and may be carried to the mold cavity by applying pressure to the encapsulant. Particularly envisaged here is a so-called pressure molding process, in which the encapsulant is brought into contact with the mold cavity by one or more plungers. On the other hand, the present invention also compresses the sealing material in the mold cavity using the closing pressure of the molding part (pressure molding), or injects the sealing material into the mold cavity (injection). It may be combined with other sealing processes, such as molding. The application of the volume reducing material in the mold cavity can result in the above advantages regardless of the method of supplying the sealant to the mold cavity.

In a variant of the method according to the invention, the volume reducing material may be supplied to the mold cavity via a gas inlet (exhaust air or vent) before closing the mold cavity. The volume reducing material (eg in the form of steam) can thus be introduced into the mold cavity in a short time, eg within 1 to 3 seconds. Therefore, only the molding part that defines the mold cavity can be at a closed pressure.

The present invention also provides a device for sealing an electronic component mounted on a carrier, which is displaceable relative to each other and defines at least one mold cavity for enclosing the electronic component in a closed position. And a supply means for liquid sealing connected to the mold cavity, and the apparatus also provides an apparatus comprising supply means for volume reducing material connected to the mold cavity. Supply means for volume reduction material, a volume reduction member, the desired heating element for the state of may comprise a supply means for volume reduction member for supplying, for example, connected to the mold cavity It may be formed by one or more nozzles. With such a device, the advantages as already mentioned above with reference to the method according to the invention can be achieved and are considered to be included herein by reference with respect to the device according to the invention. The volume-reducing material supply can thus be incorporated into existing sealing devices with only very limited structural changes.

A variant of the device according to the invention also comprises supply means for supplying film material between the forming parts. The volume reducing material supply means and the sealing material supply means may be located on the opposite side of the film supplied by the film material supply means. With such a device in which the supply of the volume reducing material is combined with the film supply, the advantages of combining the supply of the volume reducing material and the presence of the film material during sealing can be achieved, as already explained above for the method according to the invention. These above advantages are also encompassed herein by reference with respect to the apparatus in which these two supply facilities are combined. Not only is the simple structure of the molded part with the mold cavity sufficient, but the volume reducing material is also avoided from contacting the sealing electronics. Since the volume reducing material in this variant does not contact the sealing electronic component and the carrier, the volume reducing material therefore has no undesirable effect. This improves the possibility of selecting an appropriate volume reducing material . It should also be noted that the encapsulant remains physically separated from the volume reducing material , thereby avoiding undesirable effects of the volume reducing material and the encapsulant on each other.

Simple supply of volume reduction material can be achieved if the supply means for the volume reduction material, have been made to place the volume reduction material on the film material. The volume reducing material therefore does not need to be introduced into the mold cavity by the supply means. If the film material to which the sealing material is attached is placed anywhere between the molding parts, it is sufficient that the volume reducing material is disposed on the film material. The supply of film material is therefore also used to introduce a volume reducing material between the forming parts.

  The invention will be further described based on the following non-limiting embodiments.

FIG. 1 shows a schematic perspective view of a part of a prior art device for sealing an electronic component mounted on a carrier. FIG. 2A shows two different top views of the carrier with electronic components during successive stages of the prior art sealing process. FIG. 2B shows two different top views of the carrier with electronic components during successive stages of the prior art sealing process. FIG. 3 shows a schematic side view of an apparatus for sealing an electronic component mounted on a carrier according to the invention. FIG. 4A shows a schematic side view of an apparatus for sealing an electronic component mounted on a carrier according to the present invention, the apparatus also comprising a supply for film material. FIG. 4B shows a schematic side view of an apparatus for sealing an electronic component mounted on a carrier according to the present invention, the apparatus also comprising a supply for film material. FIG. 5 shows a cross-sectional view through a part of a variant of the sealing device according to the invention with a so-called “top edge” supply for the sealing material.

FIG. 1 shows a cut-away sectional view through two molded parts 1 and 2. Disposed in the lower molding portion 2 is a recess 3 for receiving a carrier 4 (for example, a lead frame or a substrate) in which an electronic component 5 is disposed. Through the channel 6 connected to the mold cavity, the sealing material 7 is supplied to the mold cavity as indicated by the arrow P ₁ . In the situation shown, the mold cavity is only partially filled with the encapsulant 7, and the encapsulant flows into the mold cavity with the flow front 8, thereby sealing the electronic component 5.

The prior art sealing method schematically shown with reference to FIG. 1 also applies to FIG. 2A. What is shown here in a top view is a carrier 10 in which a sealing material 12 is supplied by a supply channel 11. From the supply channel 11, the encapsulant 12 flows to the distribution chamber 13, from which the encapsulant 12 flows with the flow front 14 over a large width across the carrier (film gate) as indicated by arrow P _2. . Located on the carrier 10 are the electronic components 15 that project above the surface of the carrier 10 and thus generate a predetermined resistance to the flow of the encapsulant 12 across the carrier 10. As a result, the flow front does not flow linearly across the carrier 10 but has a more complex shape that may be delayed at a position behind the electronic component 15 as shown. The sealing material has a small resistance that causes a risk of gas sealing 16 at the position (near the electronic component 15), and flows between the electronic components. This is undesirable because the gas fill 16 may form an opening in the final electronic component 15 seal. Also included in this FIG. 2A are two exhaust channels 17 for gas from the mold cavity through which the gas present in the mold cavity is passively or as indicated by arrow P _3. Actively escape.

  In FIG. 2B, the seal has reached the outer end 18 of the mold cavity located on the opposite side of the supply channel 11, and the discharge channel 17 is closed as shown schematically by a closure 19. This can be done, for example, using a V pin as previously developed by the applicant. By closing the discharge channel 17, the filling pressure of the sealing material can be increased, so that the gas filling 16 present becomes smaller or even disappears. The resulting gas encapsulation 16 within the encapsulant 12 nevertheless remains a problem that results in a failure of the encapsulated product.

FIG. 3 shows a cut-away sectional view through the two moldings 20, 21 of the sealing device 22 according to the invention. Here, similarly, disposed in the lower molding portion 21 is a recess 23 for receiving the carrier 24 in which the laminated electronic component 25 (flip chip) is disposed. The sealing material 27 can be supplied to the mold cavity 28 via a runner 26 connected to the mold cavity. The supply of the sealing material 27 is here carried out by a plunger 29 which can apply pressure to the sealing material 27. For this purpose, the plunger 29 is displaceable in a housing 30 in which the sealing material 27 is also carried. The volume reducing material 31 can be introduced into the mold cavity 26 in the form of water vapor 32, for example. It is also possible to “clean” the mold cavity 28 with volume reducing materials 31, 32, for example, before introducing the sealing material 27 into the mold cavity. The option here is to pressurize the inside of the mold cavity 28 by the suction port 33. Since the reservoir 34 having the volume reducing materials 31 and 32 is in an open connection state with the mold cavity 28, the vapor pressure is also reduced in the reservoir 34, thereby boiling the volume reducing materials 31 and 32 (for example, water). Begin to. The temperature of the volume reducing material in the reservoir 34 is selected for this purpose so that the desired boiling state of the volume reducing materials 31, 32 occurs exactly as a result of the reduced pressure. The water vapor passes through a conduit 35 having a valve 36 that is then opened to clean the mold cavity 28 and again (partially) disappear through the inlet. Of course, many other ways of cleaning the mold cavity 28 (e.g., by placing additional cleaning conduits in the upper mold 20 ) are possible. Once the mold cavity 28 is filled with the volume reducing material 32 in the vapor state (or at least substantially all of the air has completely disappeared from the mold cavity), by closing the valve 36, Washing can be stopped. The encapsulant 27 can then be pressed into the mold cavity by the plunger. It should be noted here again that there are many other ways in which the encapsulant can be introduced into the mold cavity, perhaps extra. These alternative methods of supplying the encapsulant also form part of the present invention in combination with filling the mold cavity with a volume reducing material .

  FIG. 4A shows a cross-sectional view through a sealing device 37 according to a variant embodiment of the invention comprising two moldings 20, 21 connected to the opposite side of the carrier 24 with the electronic component 25. In the sealing device 37, the lower molding portion 21 similarly includes a flat contact side 23 that supports the carrier 24. The molding unit 20 includes a mold cavity 40 that encloses a plurality of electronic components.

What is supplied between the forming parts 20 and 21 by the supply roller 45 is the film material 38 that is discharged again to the discharge roller 46 after one or more steps. The film material is supplied to the carrier 24 and the film material 38 (hence the FIG. 4B) by the supply means for the sealing material 42 connected to the intermediate region 39 to be created between the carrier 24 and the film material 38. A separation layer is formed on one side to which the sealing material can be supplied. The volume reducing material supply means 41 is placed so that the volume reducing material can be supplied onto the film material 38 as indicated by an arrow P ₅ before the film material is conveyed between the molding parts 20 and 21. During the supply of the film material 38, the volume reducing material is then also supplied to the location where the mold cavity 40 is located. The liquid sealing material is then guided between the film material 38 and the carrier 24 by the supply means 42 as indicated by arrow P ₄ . As a result of the pressure of the encapsulant and the phase change of the volume reducing material in the mold cavity 40, the film 38 is moved toward the wall of the mold cavity 40 (see FIG. 4B). Due to the possibility of gas discharge and surplus sealing material (arrow P ₆ ), the vent hole 43 is left in a state of nothing by the molding part.

FIG. 5 shows a part of a sealing device 50 having an upper molding part 52 and a lower molding part 51 assembled from a plurality of relatively displaceable parts. The carrier 54 is clamped between the relatively displaceable support 55 and the edge 53 so that the sealant 60 can be supplied by the plunger 59 over the upper side of the edge 53 and through the supply channel 61. Is done. One advantage of using the edge 53 is that the edge region of the carrier 54 can thus be free of sealing material. In a state where the molding parts 51 and 52 are separated and before the sealing material is supplied, the second supply channel 56 for supplying the volume reducing material is opened, so that the volume reducing material is indicated by the arrow. It can be supplied to the streets of P _7. Here, the volume reducing material passes between the film 62 placed on the carrier 54 together with the electronic component and the mold cavity 58 in the upper molding portion 52.

Claims (12)

In a method for sealing an electronic component mounted on a carrier,
A) a processing step of placing an electronic component for sealing in a mold cavity connected to the carrier;
B) a processing step of filling the mold cavity with a liquid sealing material;
C) a treatment step of at least partially curing the sealing material in the mold cavity,
-Before processing step B), a film material is arranged between the carrier with electronic components and the mold cavity connected to the carrier;
- before filling the mold cavity to processing step B) in a sealing material, is introduced volume reduction material into the mold cavity, the volume reduction material phase changes to processing step B) in it Reduces the volume of the volume reducing material ,
The liquid sealing material is supplied between the carrier and the film material, and the volume reducing material is conveyed between the film material and the mold cavity . 2. A method according to claim 1 , wherein the volume reducing material condenses at least from the gas phase while filling the mold cavity with a sealing material as in process step B). 3. A method according to claim 1 or 2 , wherein the volume reducing material is actively carried into the mold cavity in the gas phase. 3. The method according to claim 1 or 2 , wherein the volume reducing material is actively carried as a mist into the mold cavity. 3. A method according to claim 1 or 2 , wherein the volume reducing material is in a liquid phase when actively transported into the mold cavity. 3. A method according to claim 1 or 2 , wherein the volume reducing material is a solid phase when actively transported into the mold cavity. A method according to any one of claims 1 to 6, wherein the volume reduction material, wherein the selected from the group of H ₂ O (water) and C ₂ H ₅ OH (ethanol). The method according to any one of claims 1 to 7 , wherein the inside of the mold cavity is pressurized before or during the filling of the mold cavity with a sealing material as in the processing step B). Feature method. A method according to any one of claims 1 to 8, the volume reduction material before or during introduction into the mold cavity, wherein the pressurizing the mold cavity. A method according to any one of claims 1 to 9, wherein the volume reduction material, characterized in that it is supplied through the inlet for the gas before closing the mold cavity to the mold cavity And how to. In an apparatus for sealing an electronic component mounted on a carrier,
A mold part that is displaceable relative to each other and defines, in the closed position, at least one mold cavity for enclosing the electronic component;
A supply means for a sealing material connected to the mold cavity,
The device also includes
- supply means for volume reduction member to be connected to the mold cavity,
A supply means for film material between the molding parts;
With
The volume reducing material supply means and the sealing material supply means are located on the opposite side of the film supplied by the film material supply means . 12. The sealing device according to claim 11 , wherein the volume reducing material supply means is arranged to dispose the volume reducing material on a film material.

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