Patent Application
20130255875
This relates generally to electronic devices, and, more particularly, to assembling housing parts for an electronic device.
Electronic devices may include printed circuit boards and other internal components. These components may be mounted in a housing. With some devices, it may be desirable to form the housing from mating plastic housing structures.
Mating housing structures can be attached to each other using screws. However, screws may be unsightly. Other techniques may therefore be used that secure plastic housing structures without visible fasteners. For example, techniques for bonding plastic housing structures together such as ultrasonic welding, adhesive, and temperature bonding film may be used to avoid visible fasteners. These techniques may, however, pose manufacturing challenges. Ultrasonic welding can be used to join mating plastic parts, but may produce inconsistent results. Adhesives can be flammable. Temperature bonding film (TBF), which is a low melting temperature thermoplastic polymer, may become weakened when an electronic device is operated at elevated temperatures.
It would therefore be desirable to be able to provide improved ways in which to join plastic structures for electronic devices.
An electronic device may have electronic components enclosed within a plastic housing. The electronic device may include a power converter circuit or other circuitry.
The plastic housing may include first and second mating housing members. The housing may be formed by joining edge portions of the first and second mating housing members.
The housing members may be joined using heat activated thermoset polymer film. Heat activated thermoset polymer material may be heated using a metal structure such as a strip of metal that is placed along the joint between the housing members. The temperature of the metal strip and associated layers of the heat activated thermoset film may be elevated by applying current to the metal strip using an external tool or by applying current to the metal strip using the electronic components within the housing. Heat activated thermoset polymer film may be heated using a reactive multilayer metal foil. Metal heat sink layers may be interposed between the reactive multilayer metal foil and the heat activated thermoset polymer film. A heated metal ring or a heated edge portion of a plastic housing member may also be used to heat the thermoset polymer film.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.
Electronic devices may include polymer structures such as plastic housing structures. These structures may be joined using ultrasonic welding, adhesives, temperature bonding film (e.g., heat activated thermoplastic film), or heat activated thermoset film. Ultrasonic welding may leave visible artifacts along a joined seam. Adhesives may be flammable and therefore may be undesirable when used in products that operate at an elevated temperature. Thermoplastic polymers may become weakened when raised to an elevated temperature during operation of an electronic device.
To overcome these challenges, at least some of the polymer structures in an electronic device such as plastic housing structures may be joined using thermoset polymers. Thermoset polymers may be raised to an elevated temperature to allow the polymer material to soften and form a bond with other polymers. Unlike thermoplastic polymers, which can become soft if returned to an elevated temperature during use, thermoset polymers are generally heat resistant after they have been returned to room temperature following bonding. It may therefore be advantageous to use thermoset polymers such as heat activated thermoset films when forming bonds between respective plastic housing structures.
To form a polymer bond that attaches plastic housing portions to each other, heat activated thermoset polymer material can be raised to a temperature that is above the activation temperature of the thermoset polymer material (e.g., a temperature in the range of about 160-220° C.), while being sufficiently low to avoid damaging the plastic housing portions (i.e., by eliminating or at least minimizing heating of the plastic housing significantly above the glass transition temperature of the plastic housing and thereby avoiding visible damage to the plastic housing). To ensure that heat-induced artifacts such as plastic discoloration are not visible from the exterior of device 10, heat may be generated from within the joint that is formed where opposing edges of the plastic housing portions meet each other.
An illustrative electronic device of the type that may have plastic structures that are joined using heat activated thermoplastic film is shown in
Device 10 may have a portion such as portion 14 that contains a plug configured to plug into an alternating current (AC) wall outlet. The interior of device 10 may contain alternating current to direct current (DC) power converter circuitry (AC/DC power converter circuitry) for converting AC power from the wall outlet into DC power. Cable 16 may be used to route DC power to an associated device such as a tablet computer, a laptop computer, a desktop computer, a cellular telephone, a media player, a display, a display that includes a computer, a television set-top box, a wireless router, a television, or other electronic equipment. If desired, device 10 may be a computer, telephone, media player, or other electronic equipment. The example of
Housing members 12A and 12B may be joined along a seam such as joint 18 using a thermoset material such as a heat activated thermoset film. A cross-sectional side view of device 10 of
A diagram showing equipment and operations involved in assembling electronic device 10 using heat activated thermoset film is shown in
Initially, coating equipment 27 may be used to deposit a layer of material to form heat activated thermoset film 29 on release liner 26. Release liner 26 may be a sheet of release liner material such as a sheet of silicone or other polymer (e.g., polyamide, polyethylene terephthalate, polyethylene, polycarbonate, polymethylmethacrylate, etc.), paper, or other materials. Coating equipment 27 may, for example, receive a liquid precursor for film 29 and may contain spraying equipment, rolling equipment, or other equipment for depositing the liquid onto the surface of release liner 26. Heat treatment may be used to cure the deposited material to form film 29. Once cured, film 29 may be solid at room temperature.
Following formation of layer 29 on release liner 26, coating equipment 28 may be used to form conductive material layer 30 on layer 29. Coating equipment 28 may be a tool such as roller equipment for rolling a layer of conductive metal (e.g., conductive foil) onto the top of layer 29. If desired, coating equipment 28 may form other conductive materials (e.g., conductive polymers, metal silicides, etc.) on the surface of layer 29. The conductive material may be in sheet form (e.g., aluminum foil or copper foil) or may be a foil or structure that is used as a substrate for the heat activated thermoset film. The use of roller-based equipment to attach a sheet of metal to form conductive metal layer 30 is merely illustrative.
Following the formation of metal layer 30 on heat activated thermoset film 29, coating equipment 32 (e.g., equipment such as equipment 27) may be used to deposit and cure a layer of material to form heat activated thermoset film 34.
Films 34 and 29 may be characterized by an activation temperature of about 120° C. to 130° C. (or, if desired, about 100-150° C.). Housing members 12A and 12B may be formed from a polymer or other material that has the ability to remain solid at temperatures above the activation temperature of film 34 (e.g., housing members 12A and 12B may be characterized by a glass transition temperature above 150° C.). Housing members 12A and 12B may, as an example, be formed from a polymer such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), or a PC/ABS plastic blend.
During the process of forming film 34 on layer 30, film 34 may be patterned to form coated areas such as area 36 and uncoated areas such as uncoated area 38.
After forming layer 34 on layer 30 to form heat activated thermoset film structures 39, cutting tool 40 may be used to cut structures 39. Cutting tool 40 may, for example, include die cutting equipment such as a die press or laser cutting equipment such as computer-positioned laser cutting equipment that can pattern structures 39 to form a loop of heat activated thermoset film. Patterned heat activated thermoset film structures 42 may, for example, include a portion such as ring shaped (loop shaped) portion 44 in which layer 34 coats conductive layer 30 and may have a portion such as terminals 46 and 48 in which conductive layer 30 is uncoated by heat activated thermoset film 34.
Assembly tools 50 may be used to attach structures 42 to device housing structures 52 such as structures 12A and 12B. For example, tools 50 may include robotic positioning equipment or other equipment for placing loop 44 of heat activated thermoset film structures 42 face down on the edge of member 12A and peeling away release liner 26 so that layers 29, 30, and 34 remain in place on the edge of member 12A. In this configuration, the strip of material that makes up loop 44 runs along the edges of housing members 12A and 12B. Assembly tools 50 may include a press or other equipment for pressing and holding member 12B in position on mating housing member 12A (e.g., so that layers 29, 30, and 34 are held between opposing mating edges of members 12A and 12B along joint 18).
Assembly tools 50 may also include a power supply for contacting terminals 46 and 48 (e.g., power supply equipment that is external to housing 12). Once electrical contacts have been formed with terminals 46 and 48, the power supply may supply current through loop 44 of structures 42. Film 30 may be formed with a sufficiently small thickness (e.g., 100 microns or less or 1 micron or less as examples) to allow film 30 to serve as an Ohmic heating element. As current passes through film 30 in loop 44 from the power supply, film 30 will heat due to Ohmic heating. This will cause adjacent heat activated thermoset films 29 and 34 in loop 44 to form a bond between member 12A and 12B along joint 18. Internal electrical components 24 may be sealed within the cavity formed by members 12A and 12B during the use of tools 50 to form finished electronic device 10.
If desired, heat may be applied using electromagnetic induction. With this type of arrangement, power supply 50 may include a radio-frequency signal generator that produces radio-frequency electromagnetic signals at a given frequency. Structure 44 may be implemented in the form of a metal loop, a metal strip, or other conductive structure that is configured to exhibit a resonance at the given frequency (i.e., a structure having a size and shape that exhibits an electromagnetic coupling resonance at the given frequency). When radio-frequency wireless signals are supplied by equipment 50 at the given frequency, the electromagnetically coupled structures will rise in temperature, thereby heating adjacent heat activated thermoset films 29 and 34.
As shown in
During bonding of housing members 12A and 12B using thermoset films 29 and 34, exposed surfaces such as exterior cosmetic surfaces 19 of housing 12 in
Current may be applied to layer 30 of structures 42 using external equipment such as tools 50 of
Terminal 46 of heat activated thermoset structures 42 may be coupled to components 24 at node 74 using conductive paths such as path 76. Terminal 48 of heat activated thermoset structures 42 may be coupled to components 32 at node 78 using conductive paths such as path 80. Components 24 may be used to implement control circuitry for device 10. During manufacturing operations, the control circuitry can use power from source 86 to apply a current to structures 42. The current that flows through conductive layer 30 of structures 42 may elevate the temperature of layer 30 and the heat activated thermoset material in structures 42 sufficiently to activate the thermoset material and thereby attach members 12A and 12B along joint 18. Access to the functionality of circuitry 24 that permits Ohmic heating of layer 30 may be selectively enabled during manufacturing operations. Fro example, access to the ability to apply current to layer 30 may be secured using digital authentication, using software that is loaded and run on circuitry 24 only during manufacturing operations, or using other schemes to prevent inadvertent heating of layer 30 following manufacturing.
If desired, heat activated thermoset film layers 29 and 34 may be heated using a reactive multilayer foil such as foil 92 of
When it is desired to produce heat to form joint 18, an initiating electrical pulse may be applied to reactive multilayer foil 92. Once an exothermic reaction has been initiated in foil 92, the layers of foil 92 will react with each other and will produce heat. The heat from the foil may be used to elevate the temperature of heat activated thermoset film layers 29 and 34. If desired, optional layers such as layer 90 may be interposed between foil 92 and heat activated thermoset film layers 29 and 34. Layers 90 may be formed from a material such as metal or other materials that can serve as a heat sink for the heat generated by reactive multilayer foil structure 92. Use of this heat sink may help ensure that the heat generated by reactive multilayer foil structure 92 does not burn or otherwise damage heat activated thermoset film layers 29 and (i.e., the heat sink may help prevent an overly rapid rise in temperature and may help sustain an elevated temperature for an amount of time that is sufficient to activate heat activated thermoset film layers 29 and 34). As an example, reactive multilayer foil 92 may generate heat in a relatively short time period. Using heat sink layers 90, the heat that is generated by foil 92 may remain elevated above the activation temperature of heat activated thermoset film layers 29 and 34 for a more extended amount of time. If desired, a reactive process may be used that exhibits heat generation over other time periods (e.g., 1-500 ms, more than 50 ms, more than 500 ms, 0.1 to is or more, etc.). The structures of
If desired, heat may be applied to heat activated thermoset film using a heated member such as a heated metal ring. This type of arrangement is shown in
As shown in
Illustrative steps involved in using heat activated thermoset films such as films 29 and 34 to join structures such as housing members 12A and 12B together are shown in
At step 108, heat actuated thermoset film layers such as layers 29 and 34 may be assembled with other structures along the edges of members 12A and 12B that are to be joined. During the operations of step 108, material may be included in the region between members 12A and 12B to heat the heat actuated thermoset film layers. For example, a layer of metal such as metal 30 may be included to form an Ohmic heating element or a reactive metal foil and optional heat sinks may be included in configurations in which heat is to be generated using an exothermic reaction.
At step 110, heat may be applied to elevate the temperature of the heat activated thermoset film and thereby activate the heat activated thermoset film. When applying heat, internal electronic components 24 may be enclosed within the cavity formed inside mating electronic device housing members 12A and 12B. Heat may be applied to the heat activated thermoset film by applying current to an Ohmic heating element with an external tool, by using circuitry in the internal electrical components, by triggering an exothermic reaction in a reactive multilayer foil structure, by applying heat to the film from a heated metal ring, by heating a portion of members 12A and/or 12B using a heat source prior to pressing members 12A and 12B against the heat activated thermoset film, by applying electromagnetic energy (radio-frequency signals) wirelessly that are inductively coupled to a metal ring, strip, or other resonant structure (e.g., a structure such as structure 44 of
At step 112, following formation of housing 12 for device 10 by joining housing members 12A and 12B along joint 18 using heat activated thermoset film, final device manufacturing operations may be performed (e.g., to trim excess material, to apply a desired surface finish, etc.).
The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.
