GB2177965A - Manufacturing an electrical device - Google Patents

Manufacturing an electrical device Download PDF

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Publication number
GB2177965A
GB2177965A GB08518674A GB8518674A GB2177965A GB 2177965 A GB2177965 A GB 2177965A GB 08518674 A GB08518674 A GB 08518674A GB 8518674 A GB8518674 A GB 8518674A GB 2177965 A GB2177965 A GB 2177965A
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GB
United Kingdom
Prior art keywords
surplus
encapsulation
ofthe
laser irradiation
plastics material
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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GB08518674A
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GB8518674D0 (en
Inventor
Joseph Bell Titterington
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Philips Electronics UK Ltd
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Philips Electronic and Associated Industries Ltd
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Filing date
Publication date
Application filed by Philips Electronic and Associated Industries Ltd filed Critical Philips Electronic and Associated Industries Ltd
Priority to GB08518674A priority Critical patent/GB2177965A/en
Publication of GB8518674D0 publication Critical patent/GB8518674D0/en
Publication of GB2177965A publication Critical patent/GB2177965A/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/48—Manufacture or treatment of parts, e.g. containers, prior to assembly of the devices, using processes not provided for in a single one of the subgroups H01L21/06 - H01L21/326
    • H01L21/4814—Conductive parts
    • H01L21/4821—Flat leads, e.g. lead frames with or without insulating supports
    • H01L21/4835—Cleaning, e.g. removing of solder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C37/00—Component parts, details, accessories or auxiliary operations, not covered by group B29C33/00 or B29C35/00
    • B29C37/02—Deburring or deflashing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/14—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles
    • B29C45/14639—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles for obtaining an insulating effect, e.g. for electrical components
    • B29C45/14655—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles for obtaining an insulating effect, e.g. for electrical components connected to or mounted on a carrier, e.g. lead frame
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/30—Organic material
    • B23K2103/42—Plastics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/0053—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor combined with a final operation, e.g. shaping
    • B29C2045/0077—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor combined with a final operation, e.g. shaping removing burrs or flashes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/68—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts by incorporating or moulding on preformed parts, e.g. inserts or layers, e.g. foam blocks
    • B29C70/72—Encapsulating inserts having non-encapsulated projections, e.g. extremities or terminal portions of electrical components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/34—Electrical apparatus, e.g. sparking plugs or parts thereof
    • B29L2031/3406—Components, e.g. resistors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
    • H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
    • H01L2224/491—Disposition
    • H01L2224/4912—Layout
    • H01L2224/49171—Fan-out arrangements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/30—Technical effects
    • H01L2924/301—Electrical effects
    • H01L2924/3025—Electromagnetic shielding

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Power Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • Encapsulation Of And Coatings For Semiconductor Or Solid State Devices (AREA)
  • Structures Or Materials For Encapsulating Or Coating Semiconductor Devices Or Solid State Devices (AREA)
  • Mechanical Treatment Of Semiconductor (AREA)

Abstract

Laser irradiation is used to depolymerise surplus encapsulation which is in the form of a thin film extending from an encapsulation of the device. Where the surplus is a thin sheet lying for example over a heatsink or over and between leads the laser irradiation may also vaporise the surplus without damage to underlying parts of the device. Where the surplus is present as a surface layer at an external surface of the encapsulation, the laser depolymerised surplus may be removed by dry grinding with a relatively soft grinding medium. Laser radiation from a CO2 laser operating at 10.6 microns may be used at a power density between 4.5 and 22.5MWcm<-2>. The device may be a semiconductor device.

Description

SPECIFICATION A method of manufacturing an electrical device and an electrical device so manufactured The invention relates to a method of manufacturing an electrical device including an encapsulation and to an electrical device so manufactured, particularly but not exclusively where the electrical deviceisasemi- conductor device.
A known method of manufacturing such an electrical device includes the steps of moulding plastics material to form at least part ofthe encapsulation, the moulding step also forming a surplus of plastics material on the electrical device, treating the surplus and removing the treated surplus. In the known method the step of treating the surplus is separate from the step of removing the surplus.
The step oftreating such a surplus has hitherto included soaking the device to soften the surface of the plastics material and the treated material is then removed by water or grit blasting the softened surface.
In a first known treatment the device is soaked successively in a mixture of phenol, cresol and an organic acid, then in methylenechloride,then in sodium hydroxide and finally in isopropyl alcohol. In a second known treatment the device is soaked in M-pyrrole. The soaking process softens the surface of the plastics material sufficiently for the surplus to be removed by blasting with water or with a relatively soft grit medium. It is not clear however, whetherthe softening is a result of the plastics material being partly dissolved or partly depolymerized or both by the soaking treatment.
This softening by soaking treatment however has at least two disadvantages. First, the device treated must be soaked for several hours until the greatest thickness of surplus present is softened. Second, the soaking is not selective and as a result the surface of allthe plastics material is softened, notjutthatsur- face at which the surplus is present. To compensate forthis, afterthe blasttreatmentto remove the softened surplus, the device is baked to reharden the softened surface ofthe plastics material which now forms the surface of the encapsulation.
The soaking treatment and subsequent rehardening may have a further disadvantage in the manufacture of an electrical device in that the soaking may introduce chemical species into the plastics material which are retained in the plastics material when it is rehardened. These chemical species can migrate through the plastics material and may affect the operation of an electrical device or cause corrosion of device connections within the plastics material forming the encapsulation. The retention of potentially damaging chemical species is of particular importance in the manufacture of semiconductor devices where the semiconductor body may be affected by the presence of these chemical species, leading to a degradation of device performance.
The inventor has found that in semiconductor devices which have encapsulation moulded about a heatsinkthe removal ofthesurplus by the soak and blast method described above may leave encapsulation proud ofthe heatsink surface even after rehardening, due to swelling of the plastics material when soft. In semiconductor devices so formed with for example a T0220 outline the heatsink surface has been found to be spaced apart from a surface on which the devices are mounted by the encapsulation aboutthe heatsinkstanding on average 12 micrometres proud ofthe heatsink surface, thus increasing the thermal resistance between a semiconductor body within the device and the surface on which the device is mounted.The reduction ofthethermal resistanceto a desired value is usually accomplished by putting a deformable thermally conductive material such as a heatsink compound between the heatsink and the mounting surface to bring them into intimate thermal contact. When assembling circuits containing such devices the use of a heatsinkcompound is an extra, undesirable assembly step.
According to a first aspect ofthe invention there is provided a method of manufacturing an electrical device including an encapsulation which method in cludesthestepsof moulding plastics material to form at least part of the encapsulation, the moulding step also forming a surplus of plastics material on the electrical device, treating the surplus and removing the treated surplus, characterised in that, the step of treating the surplus includes a depolymerization of the surplus and the depolymerization is achieved by means of irradiation from a laser.
Such useoflaserirradiationtotreatthesurplus permits the treatment to be effected in a shorttime and in a single step, and also without the possibility of introducing solvent borne potentially damaging chemical species to the encapsulation.
The previously known need to reharden the encapsulation surface by baking the device can be avoided in a method in accordance with the invention. Due to the directional nature of the laser irradiation and a possibility of using selective shielding, the treatment can be localised to expose the surplus without affecting at least a major part ofthe encapsulation. Particularlywhen the surplus is in the form of a thin film ora thin surface layer; the surplus may even be removed by being both depolymerized and vaporized bythe laser irradiation. Thus the present invention permits a considerable simplification of the treatment and even removal ofthesurplus plastics material,furtherthe surplus may be treated and removed by an entirely dry treatment and removal.The treatment and removal of the surplus plastics material may therefore be effected in a single step in accordance with the invention.
The electrical device may have leads extending from the encapsulation and the laser irradiation is effected to depolymerize the surplus which may be formed as a thin film between and over at least part of the leads. The depolymerization bythe laser irradiation can be selective and hence limited to the surplus of plastics material. The plastics material forming the encapsulation can be at least partly shielded from the laser irradiation when the laser irradiation is effected to depolymerize a thin film of surplus material between and over at least part of the leads.
As stated hereinbefore and at least part of a thin film of surplus material between and over at least part ofthe leads may be removed by being both depolymerized and vaporized by the laser irradiation.
In a method of manufacturing an electrical device in accordance with a first aspect of the invention the encapsulation may be formed with a heatsink recessed in an external surface and the laser irradiation is effected to depolymerize the surplus which may be formed as a thin film over at least part of an external surface ofthe heat sink. The step oftreating the surplus plastics material may be effected by laser irradiation andthethin film of surplus may be both treated and removed by the combined effect of depolymerization and vaporization bythe laser irradiation.
The encapsulation may be formed with a heatsink recessed in an external surface and with at least part ofthe surplus as a surface layer at said external surface ofthe encapsulation and said external surface may be subjected to the laser irradiation to depolymerize the plastics material to a depth sufficient to leave the heatsink pround of the encapsulation after removal ofthe depolymerized surplus. An electrical device may thus be manufactured by a method in accordance with the invention to have a heatsink which stands proud ofthe surrounding encapsulation. Such an electrical device may be mounted on a heatsinking surface and the heatsink may achieve an intimate thermal contact with the heatsinking surface without there being-a deformablethermally conduc tivematerial between the heatsink and the mounting surface.
Part ofthe surplus eitherformed as a thin film over atleastpartofan external surface of the heatsinkor formed as a surface layer at the external surface ofthe encapsulation may be removed by being both depolymerized and vaporized bythe laser irradiation.
The part of the surplus which remainsafterthe irradiation may be removed by dry grinding.
The plastics material may be a silica filled epoxy resin which is known to adhere tenaciously to surfaces of nickel plated copper conductors widely used for leads and heatsinks of electrical devices, particularly semiconductor devices.
The surplus may be exposed to irradiation incident at a power density which lies between 4.5 MWcm9 and 22.5 MWcm#2. The incident power density may be achieved by more than one exposure ofthe surplus to the laser irradiation or by focussing means between the laser and the surplus to be irradiated or both.
To preventtheformation of an airplasma in the beam the laser irradiation may be incident at a non zero angle ofincidenceto any majorreflecting surface present on the device.
The carbon dioxide gas laser operating at a wavelength of 10.6 micrometres may be used to pro videthe irradiation. Radiation atthiswavelength is well absorbed bythe plastics materials used for device encapsulation.
According to a second aspect of the invention there is provided an electrical device including an encapsulation and manufactured by a method in accordance with a first aspect of the invention.
Embodiments of the invention will now be described, byway of example only, with reference to the accompanying drawings, in which: Figures lA-D show schematically steps in a method in accordance with the invention of manufacturing an 8 lead semiconductor device including an encapsulation, Figures 1A and 1C being plan views, Figure 1B being a section of line M-M of Figure 1Aand Figure 1D showing a section on line L-L of Figure 1 C. In Figure 1 D the internal structure of the device is omitted for clarity.
Figures 2A-Eshow schematically steps in a method in accordance with the invention of manufacturing a semiconductor device including an encapsulation in which the encapsulation is formed with a heatsink recessed in an external surface, Figures 2A and 2C being plan views, Figure 2B being a section on line X-X of Figure 2A and Figure 2D showing a section on line Y-Y of Figure 2C.
Figure 2F sh ows a schematic cross section of a semiconductor device manufactured by a method in accordance with the invention and mounted against a heatsinking surface.
Figure 1Aand Figure 1B,showingtheviewon M-M of Figure lA, showschematicallya stage in the manu- facture of an 8 lead semiconductor device before the moulding of plastics material to form an encapsulation. The moulding may be performed by any one of a number of known pressure moulding methods, for example injection moulding, commonly used for thermoplastic materials ortransfer moulding, commonly used fotthermosetting plastic materials.
In both Figures 1Aand 1 B a semiconductor body 1 is attached to an alumina substrate 2. Also attached to the alumina substrate are the inner ends 3A of the device external leads 3. The inner ends of the external leads are connected by inner leads 4 to the semiconductor body. The outer ends 3B of the external leads 3 extend to a surrounding lead frame 5. The lead frame 5 is provided with index holes 6. The encapsulation mould is not shown, but is is formed to accommodate the external leads and lead frame and provide a void aboutthe semiconductor body 1, substrate 2, internal leads 4 and inner ends 3A ofthe external leads 3 into which the plastics material is moulded to form the encapsulation. The void is outlined by the dot-dash line7 in the Figures.For ease of use, the mould is made in two separable pieces aboutthe mid plane of the lead frame 5 and external leads 3 as indicated by dashed line 8 of Figure 1 B.
Afurtherstage in the method is shown schematic allyin Figure 1 C.
During the step of moulding the plastics material form the encapsulation 9, the moulding pressure can force plastics material between the pieces of the mould. Thusthe moulding steps also forms a surplus of plastics material on the device and that surplus is formed as a thin film 10 between and over at least part of the external leads 3. The thickness of the surplus may be on average 15 micrometres adjacent the encapsulation 9,thinning furtherfrom the encapsula tionwhen an epoxy resin based plastics material is moulded to form the encapsulation.
Laser irradiation, provided by a laser 11, is effected to depolymerize the thin film 10 of surplus plastics material. The external surface 12 of the encapsulation 9 may be shielded from the laser irradiation by shield 13. Thethin film 10 may be removed by being both depolymerized and vaporized bythe laser irradiation and in this case further mechanical removal is limited to a brushing of the external leads 3 to remove 'smoke' marks deposited thereon from the vaporized surplus.
In Figure 2A and Figure 2B, a semiconductor device 20 of T0220 outline is shown held in a section of lead frame 2l,afterthe step of moulding plastics material to form an encapsulation 9 in a method similartothat described with respect to Figures 1 A and 1 B above.
The encapsulation 9, however, is formed with a heatsink 22 recessed in an external surface 25 ofthe encapsulation 9 and the surplus plastics material is formed either as a thin layer 23A over at least part of the external surface 24 ofthe heatsink22 oras a surface layer 23B at the external surface 25 ofthe encapsulation 9 or both. Surplus plastics material may also be present as a thin film 10 between and over at least part ofthe external leads 3. The thin film 10 may be treated and removed as described above with reference to Figures 1A-D.
Laser irradiation isthen effected, as shown in Figures 2C and 2D, to depolymerize the surplus plastics material thin layer 23A and surface layer 238. The plastics material may be depolymerised to a depth sufficient to leave the heatsink proud ofthe encapsulation after removal of the surface layer 23B. At least part of the surplus thin layer 23A and surface layer 23B may be removed by being both depolymerized and vaporized bythe laser irradiation. Any depolymerized part of the surplus which remains afterthe irradiation may be removed by dry grinding. The depolymerized surplus is sufficiently soft that a soft grinding medium 32 in Figure 2E may be used.
The plastics material which is moulded to form the encapsulation may be a silica filled epoxy resin plastic. The depolymerization treatment which may be used for such a plastics material is an exposure to laser irradiation incident at a power density which lies between 4.5 MWcm9 and 22.5 MWcm9 at a wavelength of 10.6 micrometres. Irradiation of a sur plus of plastics material at an external surface of an encapsulation (for example surface layer 23B) at 4.5 MWcm#2 vaporizes approximately 1 micrometre of the surplus and depolymerizes the remainderto a depth of approximately 4 micrometres and irradiation at 22.5 MWcm#2 vaporizes approximately 6 mic rometres and depolymerizes the remainderto a depth of approximately 30 micrometres.These vaporization and depolymerization depths are necessarily affected by the underlying encapsulation and in contrast where irradiation is performed on surplus plastics material intheform of a thin film (forexample thin film 10 orthin layer23A) at a power densityof4.5 MWcm#2 approximately 15 micrometres of plastics material is vaporized. The incident power density may be achieved by more than one exposure ofthe surplus to the laser irradiation or by a focussing means between the laser 11 and the surplus to be irradiated. The focussing means may be a cylindrical lens 26 which with an associated aperture 27 gives a rectangular irradiation area 28 which is smallerthan the surplus to be irradiated.To expose the whole surplus to the irradiation the device may be fed by a traverse mechanism (notshown)inthedirectionof arrow A beneath the rectangular irradiation area to give adjacent exposed areas El to E5.
An appropriate power density may be selected in accordance with the thickness ofsurplus to bedepolymerized and the depolymerized surplus may then be removed by dry grinding with a soft grinding medium. It is common to use nickel plated copper for the heatsinks and leads and lead frame of semiconductor devices.
As shown in Figure 2E the hardness of the nickel plated lead frame 21 and heatsinksurface 24 relative to the grinding wheel 32 is such as to deflect the soft grinding wheel atthe grinding contact area 33 so that whatever depth of plastic is depolymerised beneath the heatsink surface 24 the heatsink surface stands approximately 4 microns proud ofthe surrounding encapsulation after grinding. The laser irradiation power density may be adjusted to give a depolymerization ofthe surplus to a depth of 4 micrometres below the heatsinksurface leaving an encapsulation surface 25 after grinding which is fully polymerised.
The resulting device, shown in section in Figure 2F has a heatsink surface 24 proud of surrounding encapsulation 9, permitting intimate thermal contact between the heatsink surface 24 and a heatsinking surface 30 and thus providing a low thermal resistance between a semiconductor body 29 and the mounting surface. As with accepted grinding practice, the wheel rotation Rat the grinding contact area 33 is opposite to the feed direction F of the device underthe grinding wheel. The feed mechanism may be linked to or integral with the traverse mechanism which provides motion A in Figures 2C and 2D. Integration of the feed and traverse mechanisms may be required where a single laser depolymerization and removal work station is required.
The laser irradiation may be incident at a non-zero angle of incidence ato any major reflecting surface present on the device irradiated, for example leads 3 or heatsink surface 24to prevent reflections forming an air plasma which might damage the device being irradiated. Where the surplus is in the form of a thin film, for examplethin film 10 orthin layer 23A and it lies over a reflecting surface such as a nickel plated lead orheatsink,the reflection ofthe irradiation may assist in depolymerizing and vaporizing a greater thickness of plastics material than would be expected for plastics material in contact with a thermal sink provided by the heatsink and leads.
The laser 11 may be a carbon dioxide gas laser operating at a wavelength of 10.6 micrometres.
The embodiments described herein should not be considered as a limittothescopeoftheinvention.
Similar problems with the formation of surplus plastics material arise in the moulding of encapsulation forotherdevices. Forexamplethe method of manufacturing an electrical device may provide and a device so manufactured in accordance with aspects of the invention may be either a capacitor, a relay, a transformer or a resistor. Forms of such devices include encapsulations and are susceptible to the retention of potentially damaging chemical species within the encapsulation. Such devices including encapsulations are intended for use in circuitry associated with semiconductor devices so that common methods of circuit assembly, for example wave soldering, may be used.

Claims (17)

1. A method of manufacturing an electrical device including an encapsulation which method includes the steps of mouiding plastics material to form at least part of the encapsulation, the moulding step also forming a surplus of plastics material on the electrical device, treating the surplus and removing the treated surplus, characterised in that the step of treating the surplus includes a depolymerization of the surplus and the depolymerization is achieved by means of irradiation from a laser.
2. A method as claimed in Claim 1, in which the electrical device has leads extending from the encapsulation and the laser irradiation is effected to depolymerize the surplus which is formed as a thin film between and over at least part of the leads.
3. A method as claimed in Claim 2, in which the plastics material forming the encapsulation is at least partly shielded from the laser irradiation when the laser irradiation is effected to depolymerize the thin film of surplus material between and over at least part ofthe leads.
4. A method as claimed in any one ofthe preceding claims, in which the encapsulation isformedwith a heatsink recessed in an external surface and the laser irradiation is effected to depolymerize the surplus which is formed as a thin film over at least part of an external surface ofthe heatsink.
5. A method as claimed in any one ofthe preceding claims, in which the encapsulation is formed with a heatsink recessed in an external surface and with at leastpartofthesurplusasasurface layeratsaid external surface ofthe encapsulation and said external surface is subjected to the laser irradiation to depolymerizethe plastics material to a depth sufficientto leave the heatsink proud of the encapsulation after removal ofthe depolymerized surplus.
6. A method as claimed in any one of the preceding claims, in which at least a part of said surplus is removed by being both depolymerized and vaporized bythe laser irradiation.
7. A method as claimed in Claim 6, in which a depolymerized part of said surplus which remains after the irradiation is removed by dry grinding.
8. A method as claimed in any one ofthe preceding claims in which the plastics material is a silica filled epoxy resin.
9. A method as claimed in any one of the preceding claims in which the surplus is exposed to irradiation incident at a power density which lies between 4.5 MWcm#2 and 22.5 MWcm#2.
10. Amethod as claimed in Claim 9, in which the incident power density is achieved by more than one exposure ofthe surplus to the laser irradiation.
11. A method as claimed in Claim 9 or Claim 10, in which the incident power density is achieved by focussing means between the laser and the surplus to be irradiated.
12. A method as claimed in anyone ofthe preced- ing claims, in which the laser irradiation is incident at a non-zero angle of incidence to any major reflecting surface present on the device.
13. Amethod as claimed inanyoneofthepreced- ing claims, in which the laser is a CO2 gas laser operating at a wavelength of 10.6 micrometres.
14. A method as claimed in any one ofthe preceding claims, in which the device is a semiconductor device.
15. An electrical device manufactured by a method as claimed in any preceding claim.
16. A method of manufacturing an electrical device substantially as herein described with reference to Figures 1A-D or Figures 2A-E.
17. An electrical device substantially as herein describedwith referenceto Figure2F.
GB08518674A 1985-07-24 1985-07-24 Manufacturing an electrical device Withdrawn GB2177965A (en)

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GB2266262A (en) * 1991-10-31 1993-10-27 Dunlop Automotives Composites Removal of spurious formations formed during moulding of plastics articles
EP0905762A1 (en) * 1997-09-30 1999-03-31 STMicroelectronics S.r.l. Method for removing moulding residues in the fabrication of plastic packages for semiconductor devices
US5987740A (en) * 1996-10-22 1999-11-23 Vlt Corporation Laser machining of molded assemblies
EP1052691A2 (en) * 1999-05-10 2000-11-15 Intersil Corporation Laser decapsulation apparatus and method
EP1130637A1 (en) * 2000-03-03 2001-09-05 STMicroelectronics S.r.l. A method of removing moulding residues during the manufacture of plastic packages for semiconductor devices
US6483706B2 (en) 2000-12-22 2002-11-19 Vlt Corporation Heat dissipation for electronic components
DE10154017A1 (en) * 2001-11-02 2003-05-15 Atmel Germany Gmbh Method for accessing electronic components in cast housing which have contact surface enclosed in housing comprises exposing surface using laser beam which is switched off when end point signal is produced
DE10154021A1 (en) * 2001-11-02 2003-05-15 Atmel Germany Gmbh Method for accessing electronic components in cast housing which have contact surface enclosed in housing comprises exposing surface using laser beam which is switched off when end point signal is produced
US7125729B2 (en) 2001-11-02 2006-10-24 Atmel Germany Gmbh Method for opening the plastic housing of an electronic module
EP2111636A1 (en) * 2006-12-21 2009-10-28 Agere Systems, Inc. High thermal performance packaging for circuit dies
JP2013214775A (en) * 2013-07-17 2013-10-17 Renesas Electronics Corp Method for manufacturing semiconductor device
JP2014003346A (en) * 2009-07-06 2014-01-09 Renesas Electronics Corp Semiconductor device manufacturing method

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Publication number Priority date Publication date Assignee Title
GB2266262B (en) * 1991-10-31 1996-07-03 Dunlop Automotives Composites Manufacture of plastics articles
GB2266262A (en) * 1991-10-31 1993-10-27 Dunlop Automotives Composites Removal of spurious formations formed during moulding of plastics articles
US5987740A (en) * 1996-10-22 1999-11-23 Vlt Corporation Laser machining of molded assemblies
US6468356B1 (en) 1997-09-30 2002-10-22 Stmicroelectronics S.R.L. Method for removing molding residues in the fabrication of plastic packages for semiconductor devices
EP0905762A1 (en) * 1997-09-30 1999-03-31 STMicroelectronics S.r.l. Method for removing moulding residues in the fabrication of plastic packages for semiconductor devices
US6335208B1 (en) * 1999-05-10 2002-01-01 Intersil Americas Inc. Laser decapsulation method
US7316936B2 (en) 1999-05-10 2008-01-08 Intersil Americans Inc. Laser decapsulation method
USRE43980E1 (en) 1999-05-10 2013-02-05 Intersil Corporation Laser decapsulation method
EP1052691A2 (en) * 1999-05-10 2000-11-15 Intersil Corporation Laser decapsulation apparatus and method
EP1052691A3 (en) * 1999-05-10 2003-11-05 Intersil Corporation Laser decapsulation apparatus and method
USRE42193E1 (en) 1999-05-10 2011-03-01 Intersil Corporation Laser decapsulation method
US7166186B2 (en) 1999-05-10 2007-01-23 Intersil Americas Inc. Laser decapsulation apparatus and method
EP1130637A1 (en) * 2000-03-03 2001-09-05 STMicroelectronics S.r.l. A method of removing moulding residues during the manufacture of plastic packages for semiconductor devices
US6483706B2 (en) 2000-12-22 2002-11-19 Vlt Corporation Heat dissipation for electronic components
DE10154021A1 (en) * 2001-11-02 2003-05-15 Atmel Germany Gmbh Method for accessing electronic components in cast housing which have contact surface enclosed in housing comprises exposing surface using laser beam which is switched off when end point signal is produced
US7125729B2 (en) 2001-11-02 2006-10-24 Atmel Germany Gmbh Method for opening the plastic housing of an electronic module
DE10154017A1 (en) * 2001-11-02 2003-05-15 Atmel Germany Gmbh Method for accessing electronic components in cast housing which have contact surface enclosed in housing comprises exposing surface using laser beam which is switched off when end point signal is produced
EP2111636A1 (en) * 2006-12-21 2009-10-28 Agere Systems, Inc. High thermal performance packaging for circuit dies
EP2111636A4 (en) * 2006-12-21 2014-09-10 Agere Systems Inc High thermal performance packaging for circuit dies
JP2014003346A (en) * 2009-07-06 2014-01-09 Renesas Electronics Corp Semiconductor device manufacturing method
US9087850B2 (en) 2009-07-06 2015-07-21 Renesas Electronics Corporation Method for manufacturing semiconductor device
US9263274B2 (en) 2009-07-06 2016-02-16 Renesas Electronics Corporation Method for manufacturing semiconductor device
JP2013214775A (en) * 2013-07-17 2013-10-17 Renesas Electronics Corp Method for manufacturing semiconductor device

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