WO2006011791A2

WO2006011791A2 - Method for encapsulating an electronic component using a plastic object, and plastic object

Info

Publication number: WO2006011791A2
Application number: PCT/NL2005/000544
Authority: WO
Inventors: Franciscus Bernardus Antonius De Vries; Wilhelmus Gerardus Jozef Gal
Original assignee: Fico B.V.
Priority date: 2004-07-30
Filing date: 2005-07-26
Publication date: 2006-02-02
Also published as: MY151694A; WO2006011791A3; TW200614453A; NL1026749C2; CN101040373B; TWI373830B; CN101040373A

Abstract

The invention relates to a method for encapsulating an electronic component in a mould by the processing steps of: placing the component into a mould cavity, feeding encapsulating material, and curing the encapsulating material, wherein the electronic component is shielded by an object. The invention also relates to an object

Description

Method for encapsulating an electronic component using a plastic object, and plastic object

The invention relates to a method as according to the preamble of claim 1. The invention also relates to a thermoplastic plastic object as according to the preamble of claim 13.

In the encapsulating of electronic components, which are normally placed on a carrier, such as more particularly semiconductor circuits, a part of the component and/or the carrier can be shielded from the encapsulating material to be arranged. Use is made here according to the prior art of adhesive foil material which is adhered to the product for encapsulating. The foil layer can herein have, at least prior to arranging of the foil layer, permanent adhesion or the adhesion can be enhanced, usually shortly before arranging of the foil, by for instance increasing the temperature of the foil. Another option is to make use of non-adhesive foil material (also known as release film). Such a non- adhesive foil material is placed together with a product for encapsulating into a mould, wherein the foil material is held in the shielding position by means of applying pressure, wherein the foil material has a blocking effect on the parts recessed in the carrier which are to be closed off. After the encapsulating operation the encapsulated product can be removed in simple manner from the foil without the danger of residues of adhesive being left behind on the encapsulated product. The use of non-adhesive foil material does however have the drawback of increasing costs. The foil material, which can usually only be used once, does after all have to be of sufficient high quality to function under the extreme conditions occurring during the encapsulation of electronic components. Such foil material is expensive.

The object of the present invention is to provide an improved method for encapsulating an electronic component in a mould and a cover material to be applied therein which, while retaining the advantages of the prior art, is less costly in use.

The present invention provides for this purpose a method of the type stated in the preamble, characterized in that at least the contact side for connecting the releasable object to the electronic component is modified, before this object is brought into contact with the electronic component for encapsulating, such that links are arranged in the molecular chains of the plastic. The plastic is here preferably a thermoplastic plastic. This modification must take place over at least a part of the thickness of the object, although a very thin surface layer of only a few μm may already be sufficient. The modification must moreover be such that the melting point of the thermoplastic plastic, which before modification was below the temperatures occurring in the mould during encapsulation, is no longer present in the temperature range among these temperatures occurring in the mould. This means in practice that a melting point of the modified thermoplastic plastic is increased to at least 160DC, but preferably to at least 175DC, or that the modification results in a melting point disappearing completely. The arranging of links between the (macromolecular) molecules is also referred to as cross-linking of the molecules; the desired disappearance of the melting point (or melting range) will hereby take place at these temperatures occurring in the mould. Owing to the increased number of links between the molecules of the thermoplastic plastic during modification, the properties of a thermoplastic material can be influenced so as to thus obtain a more thermosetting behaviour of the material. The desired shielding can thus be realized using a relatively inexpensive plastic (compared to the non-adhesive release foil applied according to the prior art which is manufactured from polymers containing fluorine, such as for instance PTFE and ETFE). A further advantage is that at least one additional degree of freedom is created for determining the most desirable properties of the object (the period of irradiation, the intensity of the applied radiation, the direction of the radiation and so forth). Yet another option is to vary the properties of the object within the object. This means that it is for instance possible to irradiate two opposite strips less than a central web of the material such that the behaviour at the edges of the object is more thermoplastic than at the position of the central and more intensively irradiated web. It is otherwise noted that in this patent application the term "electronic component" is also understood to mean a composite product consisting of a carrier with one or more electronic components connected to such a carrier. Such a carrier is also known as a "lead frame" or "board". It is possible to opt for at least partial shielding of the actual electronic component and/or the carrier with the foil layer so as to thus keep the covered material part free of encapsulating material or fractions of the encapsulating material (such as thinner fractions of the encapsulating material referred to for instance as bleed). This is particularly advantageous in the encapsulating of electronic components placed on a carrier with continuous openings, which carrier must be covered on one side during performing of the encapsulating process (examples hereof are leadless packages such as MAP QFNs).

The plastic object can be modified by means of allowing ionizing radiation, for instance in the form of gamma radiation, to act on the foil layer and/or by directing an electron beam at the object. The modification of the molecular structure of the thermoplastic plastic foil layer consists of arranging more links between the macromolecular chains of the thermoplastic (cross-linking). The additional links will contribute toward the absence of a melting point/softening range in the temperature range at the temperatures occurring in the mould. Such a modification of the molecular structure can be readily obtained by allowing gamma radiation to act on the foil layer which can be generated using the radio-isotope Cobalt 60 used as energy source in gamma irradiation plants. Another method of arriving at the desired increase in the number of links between the plastic molecules consists of directing an electron beam at the foil layer. Electrons are normally generated here under a high vacuum and using a heated cathode. Such an irradiation thus results in a minimal investment per unit of foil material when larger quantities of foil material are irradiated simultaneously. An advantage of the use of ionizing radiation is that the starting material can be extremely simple and that the action of the ionizing radiation is the only change to existing methods.

The plastic object can also be modified by means of arranging in the object an additive substance (material) whereby links in or between the molecular chains of the thermoplastic plastic are formed in chemical manner. Examples of materials suitable for this purpose are radical-forming substances such as for instance peroxides and silanes. The chemical method of causing an increase in the number of links between the plastic molecules has the advantage that it makes the use of a radiation source unnecessary, and that it results in a controllable manner in the desired increase or disappearance of the melting point/melting range of the plastic.

Such modifications can be advantageously performed in batch- wise manner by treating larger quantities within a determined period of time. The modification of a foil layer can thus take place separately of the processing steps A) - C) at a location which can be optimized for carrying out the modification. Conversely, it is also possible for the modification of the thermoplastic plastic object to take place in continuous manner. In such a situation the irradiation of or addition of chemicals to the object can be performed in line with a production machine or an encapsulating device by a preferably compact "douceur".

In a preferred variant the modified thermoplastic plastic object comprises a foil layer. Such a foil layer can be suitable for once-only or for multiple use, and the application of foil material in encapsulating devices need not be a cause of problems. On the other hand it is also possible to envisage other objects, such as for instance in the form of a thicker material part, for instance a block. Such a block is particularly suitable for multiple use. One possibility is to integrate the block with an encapsulating device such that when the component for encapsulating is clamped between mould parts the block engages releasably on the component/the carrier of the component without this entailing extra handling of the sealing material (in this case the block).

In order to press the foil layer with sufficient pressure against the electronic component for encapsulating it is desirable to clamp the electronic component for encapsulating between at least two mould parts during processing step B). Such moulds (with at least two mould parts displaceable relative to each other) are applied on a large scale.

The invention also provides a thermoplastic plastic object for at least partially shielding electronic components, or carriers connected to the electronic components, during the feed of encapsulating material to the electronic components, characterized in that the molecular structure of at least the contact side of the plastic object is provided with links in or between the macromolecular chains. The thermoplastic plastic object can comprise a polyolefin such as for instance polyethylene, polypropylene and/or PE-X. It has not been possible heretofore to employ such materials as sealing material during the encapsulation of electronic components. In addition to the plastics mentioned in this paragraph, copolymers and mixtures derived from these materials in which said materials predominate can of course also be applied. These materials (copolymers and mixtures) also fall within the scope of protection of the present invention.

In a preferred embodiment, the plastic object is supported by a support layer. Such a support layer preferably comprises a polymer (for instance a polyester such as a polyethylene terephthalate). Conversely, the support layer can also be formed from a non-plastic material. With a multilayer object the desired properties for the release material (non-adhesive properties) can be combined with other desired properties of the object, such as for instance minimum requirements in respect of mechanical load- bearing capacity. This latter can be increased if for instance the support layer is biaxially reinforced.

In a preferred variant the thermoplastic plastic object is formed by a plastic foil layer. Application of foil materials is per se known and the peripheral equipment required therein is also available on the market. It is noted that the already used non-adhesive foils are manufactured from high-grade materials, such as for instance costly fluorine polymers. These materials have a higher melting point than the process temperature and are non-adhesive. Non-adhesive is understood to mean that there occurs at least substantially no polar bonding between foil and substrate; apart from the absence of (molecular) polar bonding, there may however be so-called "blocking" in the case of non-adhesive material, a phenomenon which indicates the occurrence of a substantial frictional resistance between the materials connecting in non-adhesive manner. The phenomenon of blocking will also occur to a determined extent in the modified plastic object according to the present invention, and even enhances a good sealing action of the plastic object. The extent to which blocking occurs depends partly on the temperature conditions.

In addition to the possible application of plastic foil material, it is also possible for the thermoplastic plastic object to be formed by a plastic block. Such a block can for instance form part of a mould part of an encapsulating device and can thus be reused many times to provide the desired sealing effect without this resulting in more complex logistics in respect of the operation of an encapsulating device.

The present invention will be further elucidated on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein: figure 1 shows a schematic view of the method according to the present invention, figure 2A shows an example of a single-layer foil according to the invention, figure 2B shows an example of a multilayer foil according to the invention, and figure 3 shows an example of a mono-material plastic block according to the invention. Figure 1 shows a number of rolls of plastic foil material 2 which are placed on a pallet 1 and which are carried past a radiation source 3. Radiation source 3 consists of a container 4 in which a radio-isotope of Cobalt is arranged. If the effect of radiation source 3 must be discontinued, it can be lowered into a water basin 5.

An irradiated roll of plastic foil material 6 is then placed adjoining an encapsulating device 7. An electronic component 11 mounted on a carrier 10 is placed between mould parts 8, 9 of encapsulating device 7 such that a mould space 12 in the upper mould part 8 can enclose component 11. The side of carrier 10 remote from component 11 rests on the irradiated foil material 13 which is unwound from roll 6. After the encapsulating operation has been performed, the irradiated foil material 13 is advanced such that an encapsulated electronic component 14 is moved outside the encapsulating device. The now used, irradiated foil material 15 is wound onto a roll 16 once the encapsulated electronic component 14 with associated carrier 17 has been removed from the irradiated foil material 15.

Figure 2A shows a roll 20 of irradiated thermoplastic plastic foil material 21, a part of which has been unrolled. Clearly shown is that foil material 21 consists of a single material layer. Figure 2B shows a roll 22 of thermoplastic plastic foil material 23 which consists of two material layers 24, 25. An upper material layer 24 is manufactured from for instance polyethylene and a lower support layer 25 is manufactured from for instance polyethylene terephthalate. In order to connect these layers to each other an adhesive layer which is very thin and therefore not shown in this figure can be applied between the two material layers 24, 25, this adhesive layer consisting for instance of acrylic glue.

Figure 3 shows schematically a cross-section through an encapsulating device 30 with two mould parts 31, 32 which are mutually displaceable. A mould cavity 33 is recessed into upper mould part 32. Arranged in lower mould part 31 is a recess 34 in which a plastic block 35 according to the present invention is placed. By placing a lead frame (not shown) on block 35, this latter will protrude during operation of encapsulating device 30 and after closing of mould parts 31, 32, and seal the lead frame placed on block 35 without the block 35 adhering to the lead frame.

Claims

1. Method for encapsulating an electronic component in a mould, in particular a semiconductor circuit, by the processing steps of: A) placing the electronic component for encapsulating into a mould cavity,

B) feeding an encapsulating material to the mould cavity, and

C) at least partially curing the encapsulating material in the mould cavity, wherein the electronic component for encapsulating is at least partially shielded during processing step B) by a releasable object manufactured from a plastic, characterized in that at least the contact side for connecting the releasable object to the electronic component is modified, before this object is brought into contact with the electronic component for encapsulating, such that links are arranged in the molecules of the plastic.

2. Method as claimed in claim 1, characterized in that the plastic object is modified by means of allowing ionizing radiation to act on the object.

3. Method as claimed in claim 2, characterized in that the plastic object is modified by means of allowing gamma radiation to act on the object.

4. Method as claimed in any of the foregoing claims, characterized in that the plastic object is modified by means of directing an electron beam at the object.

5. Method as claimed in any of the foregoing claims, characterized in that the plastic object is modified by means of arranging in the object an additive substance whereby links between the molecules of the thermoplastic plastic are formed in chemical manner.

6. Method as claimed in claim 5, characterized in that at least a part of the additive substance added to the object for forming links between the molecules consists of radical-forming additive substances.

7. Method as claimed in claim 5 or 6, characterized in that at least a part of the additive substance added to the object for forming links between the molecules consists of peroxides and/or silanes.

8. Method as claimed in any of the foregoing claims, characterized in that the modification of the thermoplastic plastic object takes place in batch- wise manner.

9. Method as claimed in any of the foregoing claims, characterized in that the modification of the thermoplastic plastic object takes place in continuous manner.

10. Method as claimed in any of the foregoing claims, characterized in that the modification of the thermoplastic plastic object takes place separately of the processing steps A) - C).

11. Method as claimed in any of the foregoing claims, characterized in that the modified thermoplastic plastic object comprises a foil layer.

12. Method as claimed in any of the claims 1-10, characterized in that the modified thermoplastic plastic object is a block.

13. Thermoplastic plastic obj ect for at least partially shielding electronic components, or carriers connected to the electronic components, during the feed of encapsulating material to the electronic components, characterized in that the macromolecular structure of at least the contact side of the plastic object is provided with links between the molecular chains.

14. Thermoplastic plastic object as claimed in claim 13, characterized in that the thermoplastic plastic object comprises poly olefin.

15. Thermoplastic plastic object as claimed in claim 13 or 14, characterized in that the plastic object comprises polyethylene.

16. Thermoplastic plastic object as claimed in any of the claims 13-15, characterized in that the plastic object comprises polypropylene.

17. Thermoplastic plastic object as claimed in any of the claims 13-16, characterized in that the plastic object is supported by a support layer.

18. Thermoplastic plastic object as claimed in claim 17, characterized in that the support layer comprises a polymer.

19. Thermoplastic plastic object as claimed in claim 17 or 18, characterized in that the support layer is biaxially reinforced.

20. Thermoplastic plastic object as claimed in any of the claims 13-19, characterized in that the support layer comprises polyethylene terephthalate.

21. Thermoplastic plastic object as claimed in any of the claims 13-20, characterized in that the thermoplastic plastic object is formed by a plastic foil layer.

22. Thermoplastic plastic object as claimed in any of the claims 13-20, characterized in that the thermoplastic plastic object is formed by a plastic block.