WO2018169388A1

WO2018169388A1 - Plunger for feeding encapsulating material to a mould cavity

Info

Publication number: WO2018169388A1
Application number: PCT/NL2018/050142
Authority: WO
Inventors: Wilhelmus Gerardus Jozef Gal
Original assignee: Besi Netherlands B.V.
Priority date: 2017-03-16
Filing date: 2018-03-08
Publication date: 2018-09-20
Also published as: CN110382198A; JP6877568B2; KR20190122863A; JP2020512212A; KR102354031B1; TWI814721B; TW201836083A; NL2018533B1; SG11201907639WA

Abstract

The present invention relates to a plunger (1) for feeding encapsulating material to a mould cavity, comprising a closed first (2) and second (3) groove recessed into and enclosing the cylinder casing of the plunger, wherein the second groove (3) is positioned between the first groove (2) and the end surface (4) of the plunger to be directed toward the encapsulating material. The first groove (2) is provided with a scraper (5), such that the scraper (5) protrudes at least partially above the surface of the cylinder casing (6) and, optionally, the second groove (3) is provided with a sealing ring (7). The present invention further relates to a kit-of-parts for the assembly of the plunger of the present invention, a device for encapsulating electronic components mounted on a carrier comprising the plunger of the present invention and method and use of the plunger of the present invention.

Description

Plunger for feeding encapsulating material to a mould cavity

The present invention relates to a plunger for feeding encapsulating material to a mould cavity. The present invention also relates to a kit-of-parts for the assembly of the plunger of the present invention, a device for encapsulating electronic components mounted on a carrier comprising the plunger of the present invention and method and use of the plunger of the present invention.

In the encapsulation of electronic components, more particularly the encapsulation of semiconductors mounted on a carrier (lead frame, substrate or wafer), use is made of the so-called "transfer moulding process". The carrier with electronic components is herein clamped between two mould parts such mould cavities are defined around the components for encapsulating. Liquid encapsulating material is then introduced into these mould cavities and, after at least partial curing thereof, the mould parts are moved apart and the carrier with encapsulated electronic components is removed.

The feed of encapsulating material takes place by means of one or more plungers with which pressure can be exerted on a supply of encapsulating material provided for this purpose. These plungers are displaceable in a housing into which the not yet liquid encapsulating material is also carried. The plunger exerts a pressure on the encapsulating material which is heated simultaneously and/or beforehand, as a result of which the encapsulating material becomes liquid. As a response to the pressure applied by the plunger, the liquid encapsulating material flows to the mould cavity and, under the correct processing conditions, fills it completely with encapsulating material. In the displacing of encapsulating material with a plunger the fitting of the plunger on the plunger housing is critical; uncontrollable quantities of encapsulating material must be prevented from penetrating through this fitting. In an existing solution for regulating the fitting of the plunger on the plunger housing a peripheral groove is recessed into the cylinder casing of the plunger.

Encapsulating material collects in this groove which then cures and thus functions as seal in a subsequent production step. This is described for instance in US 6,200,504. It has been found in practice that such a seal made from encapsulating material functions well initially, but that after a time there is a danger of the plunger jamming in the housing. This means that the plunger engages on the plunger housing in (too) close-fitting manner via the seal made from encapsulating material.

WO 2005/102658 discloses a plunger wherein a material part is placed in the groove which only partly fills the groove. After a first use of such a plunger the material part placed in the groove can be at least partly enclosed by encapsulating material. This encapsulating material enclosing the material part will usually cure after a time. Such plunger has the advantages that replenishment of the size of the seal during use of the plunger by newly supplied encapsulating material remains possible. Consequently a good fitting of the plunger on the housing can thus be realized without this possibly resulting after some use in a plunger jamming in its housing.

However, it was found in practice that the plungers provided by the prior art still have problems relating to the creation of flash and remaining particles of cured encapsulating material in the plunger housing.

The present invention has for its object to provide an improved plunger wherein the advantages of the above-described prior art can be retained and the chance of flash and pollution of the plunger housing can be further reduced.

The invention provides for this purpose a plunger for feeding encapsulating material to a mould cavity, comprising a closed first groove recessed into and enclosing the cylinder casing of the plunger and a closed second groove recessed into and enclosing the cylinder casing of the plunger, wherein the second groove is positioned between the first groove and the end surface of the plunger to be directed toward the encapsulating material. The first groove is provided with a scraper, such that the scraper protrudes at least partially above the surface of the cylinder casing and, optionally, the second groove is provided with a sealing ring. It was found that the plunger of the present invention is still capable of providing a high pressure, i.e. a pressure of about 70 to 150 bar, exerted on the liquid encapsulating material fed to the mould cavity. By providing a scraper, the wall of the plunger housing, i.e. the plunger receiving space of a device for encapsulating electronic components mounted on a carrier, is cleaned during use of the plunger in the encapsulating process. It was found that the second groove may be provided with a sealing ring to result in a plunger having improved functionality, i.e. providing a plunger having an improved vacuum necessary to exert the pressure needed to feed the liquid encapsulating material to the mould cavity. By providing a plunger having a sealing ring provided in the second groove, good functionality of the plunger during use is still observed using liquid encapsulating material having a low dynamic (shear) viscosity, i.e. less than about 10 Pa-s, e.g. about 0.25 to 5 Pa-s. Excellent results with regard to the functionality of the plunger during use are obtained using a liquid encapsulating material having a dynamic viscosity of at least 0.50 Pa-s, e.g. a dynamic viscosity of about 1 to 2 Pa-s. In case no sealing ring is present, the minimal viscosity of the liquid encapsulating material suitable for use is subject to restrictions. It was found that by providing a plunger, wherein the second groove is not provided with a sealing ring, good functionality of the plunger during use is observed using liquid encapsulating material having a dynamic viscosity of at least 10 Pa-s.

The encapsulating material may be selected from the group consisting of thermosetting polymers, such as thermosetting plastics, thermosetting pre- polymers or thermosetting resin. Preferred encapsulating materials may be selected from the group consisting of polyester resins, polyurethanes,

polyurea/polyurethane hybrids, vulcanized rubbers, phenol-formaldehyde resins, duroplast, urea-formaldehyde foams, melamine resins, diallyl-phthalates, epoxy resins, epoxy novolac resins, benzoxazines, polyimides, bismaleimides, cyanate esters, polycyanurates, mold or mold runners, furan resins, thermoset phenolic resins and vinyl ester resins. Particular preferred encapsulating materials may be selected from the group consisting of duroplast, acrylic resins, epoxy functional resins, polyurethanes, phenolic resins, amino resins and furan resins. By providing a plunger having a first groove provided with a scraper and a second groove provided with a sealing ring, it was found that the wear of the sealing ring due to repeated use of the plunger is further reduced compared to a plunger comprising a sealing ring only, e.g. the plunger disclosed in WO 2005/102658. In fact, it was found that the time of use of the sealing ring was doubled by providing a plunger according to the present invention compared to a plunger comprising a sealing ring only.

The scraper of the present invention may be made from any material suitable for scraping cured encapsulating material from the wall of the plunger housing.

Preferably the scraper is made from a metal, such as an alloy comprising iron, copper and/or chromium. In a preferred embodiment of the present invention, the scraper is made from cast iron or steel providing excellent results on scraping the cured encapsulating material form the wall of the plunger housing.

The scraper of the present invention may be a solid ring form-fittingly arranged in the first groove of the plunger, wherein the dimensions of the solid ring are chosen such that the ring close-fittingly connects to the wall of the plunger housing.

However, to increase the flexibility of the scraper and to ease to placement of the plunger in the plunger housing, the scraper is preferable formed by a piston ring, i.e. a metal expandable piston ring provided with a slit. For example, the scraper may be selected from the group consisting of compression rings, scraper rings and combinations thereof. Good to excellent scraping results are obtained by using a scraper formed by a rectangular compression ring, a napier ring or ridge dodger ring. The scraper may also be constructed by providing a scraper formed by a combination of two rectangular compression rings. In order to construct a napier ring-like scraper or ridge dodger ring-like scraper, the outer diameter of the two combined compression rings is different. In order to obtain further flexibility of the scraper provided in the first groove of the plunger, the inner diameter of the scraper may be larger than the diameter of the first groove. Anyhow the inner diameter of the scraper should be smaller than the diameter of the part of the cylinder casing of the plunger the first groove is recessed in.

The sealing ring may be made from any material, preferably made from a plastic. Plastic is available with varying spring characteristics and can furthermore be given a temperature-resistant form. It is thus desirable that the sealing ring is heat- resistant up to a temperature of at least 120°C, preferably a temperature of at least 140°C, more preferably a temperature of at least 160°C. These are after all temperatures which can occur during the encapsulation of electronic components. More specifically envisaged is a sealing ring made from a polymer, preferably a so- called high-performance engineering polymer. Examples hereof are:

perfluoroalkoxy polymer (PFA), polytetrafluorethylene (PTFE), polyetherether ketone (PEEK), and (fluoro)silicones. Such materials are commercially available under the brand names of, among others, Teflon, Norglide, Fluoroloy, Rulon, Meldin, and Chemraz. It is however also possible for other elastomers with temperature and pressure resistance to be applied for the manufacture of the sealing ring. Another possibility is to manufacture the sealing ring from a material with a relatively high coefficient of expansion. An example of such a material are for instance copper alloys. With such a material part a biasing force can be exerted by the material part during use of the plunger (at an operating temperature in the order of magnitude of 175°C), which enhances a good sealing. In a simple but efficient form the sealing ring takes an annular form, for instance as an O-ring. Such rings are commercially available in many variations for other applications. In an embodiment of the present invention, the inner diameter of the sealing ring substantially corresponds to the diameter of the second groove.

Further, the dimensions of the sealing ring may be chosen such that the sealing ring is entirely situated below the surface of the cylinder casing. Alternatively, the dimensions of the sealing ring may be chosen such that the sealing ring protrudes at least partially above the surface of the cylinder casing.

The cylinder casing of the plunger of the present invention may be further provided with helical grooves. Preferably, the helical grooves are provided in the part of the cylinder casing of the plunger situated between the first groove and the side facing away the end surface of the plunger to be directed toward the encapsulating material. The helical grooves further facilitate the removal of encapsulating material present on the wall of the plunger housing.

The present invention also relates to a plunger for feeding encapsulating material to a mould cavity, wherein the circumferential edge of the end surface of the plunger to be directed toward the encapsulating material is provided with a chamfer, said chamfer is arranged at an angle of 5^s to 45^Q with the end surface of the plunger. It was found that by providing a plunger comprising a chamfered circumferential edge encapsulating material scraped from the wall of the plunger housing is collected by the circumferential edge of the end surface of the plunger to be directed toward the encapsulating material. The collected scrapings of (partially) cured encapsulating material can be re-used in the next feed of encapsulating material to the mould cavity. It was found that the angle of the chamfered circumferential edge with the end surface of the plunger determines the effectiveness of collection of the scrapings of encapsulating material. The effectiveness of collection is increased by using a plunger provided with a chamfered circumferential edge of the end surface wherein the chamfer is arranged at an angle of 15^s to 40^s with the end surface of the plunger, even more preferred at an angle of 25^e to 35^s, even further preferred at an angle of about 30^s.

The chamfered top edge as described above, may be combined with the plunger comprising the scraper and, optionally, the sealing ring. By providing a chamfered top edge as described above, the efficacy of the scraping function is further improved.

The present invention further relates to a kit-of-parts for the assembly of the plunger according to the present invention. The kit-of-parts comprises a plunger provided with two closed grooves recessed into and enclosing the cylinder casing of the plunger, wherein a second groove is positioned between a first groove and the end surface of the plunger to be directed toward the encapsulating material and a scraper for ring for placement in the first groove. The kit-of-parts may further comprises a sealing ring for placement in the second groove.

In another aspect of the present invention, the present invention relates to a device for encapsulating electronic components mounted on a carrier, comprising at least two mould parts which are displaceable relative to each other and which mould parts in a closed position define at least one mould cavity for enclosing one or more electronic components and feed means for liquid encapsulating material connecting to the mould cavity. The feed means are provided with at least one plunger receiving space (i.e. the plunger housing), wherein the plunger of the present invention is situated (i.e. at least the top part of the plunger comprising the first and second groove) in the at least one plunger receiving space. In one embodiment the scraper of the plunger is configured to scrape contaminants from the wall of the receiving space enclosing the plunger.

With regard to the dimensions of the scraper in relation to the wall of the receiving space enclosing the plunger, it is noted that the difference in distance between the inner diameter of the scraper and the diameter of the first groove may be smaller than the difference in distance between the cylinder casing of the of the plunger and the wall of the receiving space enclosing the plunger. Also, the outer diameter of the scraper may be chosen such that the scraper is received by the receiving space under pretension. In such preferred embodiment, the outer diameter of the scraper is larger than the diameter of the wall of the receiving space.

In case a plunger is provided wherein the circumferential edge of the end surface of the plunger to be directed toward the encapsulating material is provided with a chamfer, the chamfer may be preferably arranged at an angle of 45^s to 85^s with the wall of the receiving space. As already described above, such chamfered top edge may collect scrapings of (partially) cured encapsulating material at the chamfered top edge for re-use in the next feeding cycle of encapsulating material to a mould cavity. The effectiveness of collection of the scrapings is further increased by providing a chamfer arranged at an angle of 50^s to 75^s with the wall of the receiving space, more preferably at an angle of 55^s to 65^s and even further preferred at an angle of about 60^s. The chamfered top edge may be combined with the plunger comprising the scraper and, optionally, the sealing ring, provided in the at least one plunger receiving space of the device of the present invention.

The present invention further relates to a method for feeding encapsulating material to a mould cavity, wherein the method comprises:

a) providing an encapsulating material; and

b) feeding the encapsulating material to a mould cavity by exerting a pressure to the encapsulating material,

wherein the pressure exerted on the encapsulating material is provided by the plunger of the present invention.

The pressure exerted on the encapsulating material fed to the mould cavity may be at least 50 bar. Preferably, the pressure exerted on the encapsulating material fed to the mould cavity is at least 70 bar, at least 90 bar, at least 110 bar or at least 130 bar. Preferably, the pressure exerted on the encapsulating material fed to the mould cavity is between 70 and 150 bar. The present invention further relates to the use of the plunger of the present invention in the method described above.

The present invention will be further elucidated on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein shows: figure 1 an exploded view of the plunger of the present invention;

figure 2 a perspective view of the plunger of the present invention; and

figure 3 a detailed view of the plunger having a chamfered top edge. Figure 1 shows an exploded view of the plunger 1 for feeding encapsulating material to a mould cavity. The plunger 1 comprises a cylinder casing 6 comprising a top surface 4 and helical grooves 8. The cylinder casing 6 of the plunger 1 further comprises a first groove 2 and a second groove 3. The first groove 2 is configured to receive the scraper 5, whereas the second groove 3 is configured to receive the sealing ring 7.

Figure 2 shows a perspective view of the plunger 1 , wherein the first groove 2 and second groove 3 of figure 1 are provided with, respectively a scraper 5 and a sealing ring 7. Scraper 5 is in the form of a napier ring resulting in a recessed portion 10 between the scraper 5 and the cylinder casing 6 of the plunger 1 .

Figure 3 shows a detailed view of the top part of the plunger 1 . In figure 3, the second groove 3 is not provided with a sealing ring. The scraper 5 has the form of a napier ring resulting in a recessed portion 10 and a spring area 1 1 for providing a scraper 5 having a certain degree of flexibility. The top surface 4 is provided with a chamfered circumferential edge 9.

Claims

1. Plunger for feeding encapsulating material to a mould cavity, comprising: a closed first groove recessed into and enclosing the cylinder casing of the plunger; and

a closed second groove recessed into and enclosing the cylinder casing of the plunger,

wherein the second groove is positioned between the first groove and the end surface of the plunger to be directed toward the encapsulating material,

characterised in that the first groove is provided with a scraper, such that the scraper protrudes at least partially above the surface of the cylinder casing and that, optionally, the second groove is provided with a sealing ring.

2. Plunger according to claim 1 , characterised in that the scraper is made from a metal, such as an alloy comprising iron, copper and/or chromium.

3. Plunger according to claim 1 or 2, characterised in that the scraper is made from cast iron or steel.

4. Plunger according to any of the preceding claims, characterised in that the scraper is formed by a piston ring.

5. Plunger according to any of the preceding claims, characterised in that the scraper is selected from the group consisting of compression rings, scraper rings and combinations thereof.

6. Plunger according to any of the preceding claims, characterised in that the scraper is formed by a rectangular compression ring, a napier ring or ridge dodger ring.

7. Plunger according to any of the preceding claims, characterised in that the scraper is formed by a combination of two rectangular compression rings.

8. Plunger according to claim 7, characterised in that the outer diameter of the compression rings is different.

9. Plunger according to any of the preceding claims, characterised in that the inner diameter of the scraper is larger than the diameter of the first groove.

10. Plunger according to any of the preceding claims, characterised in that the inner diameter of the scraper is smaller than the diameter of the part of the cylinder casing of the plunger the first groove is recessed in.

1 1. Plunger according to any of the preceding claims, characterised in that the sealing ring is made from a polymer, preferably a high-performance engineering polymer.

12. Plunger according to any of the preceding claims, characterised in that the sealing ring is made from a perfluoroalkoxy polymer, polytetrafluoroethylene, polyetherether ketone, (fluoro)silicones or combinations thereof.

13. Plunger according to any of the preceding claims, characterised in that the inner diameter of the sealing ring substantially corresponds to the diameter of the second groove.

14. Plunger according to any of the preceding claims, characterised in that the dimensions of the sealing ring are chosen such that the sealing ring is entirely situated below the surface of the cylinder casing.

15. Plunger according to any of claims 1 -13, characterised in that the sealing ring protrudes at least partially above the surface of the cylinder casing.

16. Plunger according to any of the preceding claims, characterised in that the circumferential edge of the end surface of the plunger to be directed toward the encapsulating material is provided with a chamfer, said chamfer is arranged at an angle of 5^e to 45^s with the end surface of the plunger, preferably at an angle of 15^s to 40^s, more preferably at an angle of 25^Q to 35^s, more preferably at an angle of about 30^s.

17. Plunger according to any of the preceding claims, characterised in that the cylinder casing of the plunger situated between the first groove and the side facing away the end surface of the plunger to be directed toward the encapsulating material is provided with helical grooves.

18. Kit-of-parts for the assembly of the plunger according to any of the preceding claims, comprising:

- a plunger provided with two closed grooves recessed into and enclosing the cylinder casing of the plunger, wherein a second groove is positioned between a first groove and the end surface of the plunger to be directed toward the encapsulating material; and

- a scraper for ring for placement in the first groove.

19. Kit-of-parts according to claim 18, characterised in that the kit-of-parts further comprises a sealing ring for placement in the second groove.

20. Device for encapsulating electronic components mounted on a carrier, comprising:

at least two mould parts which are displaceable relative to each other and which mould parts in a closed position define at least one mould cavity for enclosing one or more electronic components; and

feed means for liquid encapsulating material connecting to the mould cavity, wherein the feed means are provided with at least one plunger receiving space, characterised in that a plunger according to any of claims 1 -17 is situated in the at least one plunger receiving space.

21 . Device according to claim 20, characterised in that the scraper of the plunger is configured to scrape contaminants from the wall of the receiving space enclosing the plunger.

22. Device according to claim 20 or 21 , characterised in that the difference in distance between the inner diameter of the scraper and the diameter of the first groove is smaller than the difference in distance between the cylinder casing of the of the plunger and the wall of the receiving space enclosing the plunger.

23. Device according to any of claims 20-22, characterised in that the outer diameter of the scraper is chosen such that the scraper is received by the receiving space under pretension.

24. Device according to any of claims 20-23, characterised in that the outer diameter of the scraper is larger than the diameter of the wall of the receiving space.

25. Device according to any of claims 20-24, characterised in that the circumferential edge of the end surface of the plunger to be directed toward the encapsulating material is provided with a chamfer, said chamfer is arranged at an angle of 45^s to 85^Q with the wall of the receiving space, preferably at an angle of 50^s to 75^e, more preferably at an angle of 55^s to 65^e, more preferably at an angle of about 60^s.

26. Method for feeding encapsulating material to a mould cavity, wherein the method comprises:

a) providing an encapsulating material; and

characterised in that the pressure exerted on the encapsulating material is provided by a plunger according to any of claims 1 -17.

27. Method according to claim 26, characterised in that the encapsulating material is selected from the group consisting of thermosetting polymers.

28. Method according to claim 26 or 27, characterised in that the pressure exerted on the encapsulating material fed is at least 50 bar.

29. Use of a plunger according to any of claims 1 -17 in a method according to any of claims 26-28.