Patent Publication Number: US-2007117268-A1

Title: Ball grid attachment

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to a method and apparatus for connecting electrical components to a substrate. More specifically, the present invention relates to a method and apparatus for providing an electrical and mechanical connection means useful for connecting electrical components, such as integrated circuits, to a substrate, such as a printed circuit board.  
      2. Description of Related Art  
      Currently many downhole tools used in the exploration and production of hydrocarbons employ sensitive electrical processing devices referred to herein as downhole electronics. One example of a downhole tool  7  having such devices is illustrated in  FIG. 1 , where the downhole tool  7  can be a perforator, logging tool, bond evaluation tool, formation testing device, or a seismic acquisition device, to name but a few. These tools are typically inserted on wireline  9  within a wellbore  12  that pierces a formation  6  of interest, and alternatingly raised and lowered within the wellbore  12  for conducting exploration and production operations.  
      As is known, electronic hardware typically involves the connection of electrical components to a substrate, where the components are often soldered to the substrate. These electrical components include digital and analog integrated circuits, processors, micro-processors, downhole sensors, cooling components, antennas, receivers, resistors, inductive elements, and capacitors, diodes, hybrids, multi-chip modules, all surface mount electronic components both passive (resistors and caps) and active (integrated circuits and op amps). The substrate provides a base on which the component is mounted and also provides dedicated electrical connectivity between various components mounted on the substrate. One example of a substrate having electrical components secured thereon is a printed circuit board. Other devices include wiring splices, connector pin to wire attachments, as well as any place where solder is typically used to make an electrical connection. Traditionally the components have pins protruding therefrom that fit into corresponding holes formed in the substrate. The pins are usually soldered within the holes to ensure electrical communication between the component and substrate and also so secure the component to the substrate.  
      Ball grid array (BGA) socket connectors are also used for electrically connecting an component to a substrate. A typical BGA includes solder balls, where each ball is attached to a tail of a corresponding conductive contact before the connector is mounted onto the substrate. After mounting, the solder ball is then later soldered to the associated substrate, thereby mechanically and electrically connecting the component to the substrate. BGA&#39;s have some advantages over other connectors; for example, it has no leads that may be easily damaged during handling. Also, solder balls are self-centering on die pads and can be easily attached to the tails of the conductive contacts. Still other advantages include smaller size, fine pitch, high density, better electrical performances, better package yields, to name but a few.  
      An example of an electrical component  19  having a BGA is shown in  FIG. 2 , the device  19  comprises a component housing  16 , a connector rod  14 , a solder ball  18 , a conductor plate  20  attached to a circuit board  22 . For the purposes of simplicity, only a single solder ball  18  of a BGA is shown in  FIG. 2 , however it is understood by skilled practitioners that a BGA can comprise a multiplicity of solder balls  18  combined with the electrical component  19 . Prior to connecting the component to the substrate, the solder ball  18  is typically soldered onto the conductor rod  14 . The component is then positioned onto the substrate and sufficient heating is applied to the solder ball  18  for it to adhere to the conductor plate  20 .  
      Certain disadvantages exist however with the current methods of manufacturing downhole electronics. For example, downhole tools often experience high shock and vibration conditions either during use within a wellbore, or during handling after they have been assembled and prior to use within a wellbore. Often times the shock or vibration can damage the downhole components thereby rendering the component inoperable or ineffective. Further, the shock and vibration during use can cause the downhole component to provide erroneous data, this is especially so when the downhole component is a sensor monitoring data downhole for later analysis. The harsh downhole conditions introduce another environmental factor that must be considered, and that is the high temperature. Downhole temperatures can sometimes exceed 200° C. Moreover, many of these electronic components generate heat that adds to the heating problem of many downhole tools. For example, the components of a typical MWD system or a system attached to a wireline, such as but not limited to, a magnetometer, accelerometer, solenoid driver, microprocessor, power supply and gamma scintillator, may generate over 20 watts of heat. These high temperatures resulting from inherent downhole conditions and generated heat can sometimes affect the integrity of the downhole electronics and their associated electronic hardware. More specifically, the repeated cycles of high heating can deteriorate the solder bond that can lead to cracks in the solder that may ultimately lead to solder failure. Moreover, the elevated temperatures can re-melt the solder connections that in turn can electrically and mechanically disconnect the components from its associated substrate.  
      A need, therefore, exists for a reliable and efficient electrical connector for electrically and mechanically connecting electrical components to an associated substrate, where the resulting connection is able to withstand wellbore conditions.  
     BRIEF SUMMARY OF THE INVENTION  
      The present disclosure includes a method of connecting an electrical component to a board substrate, wherein the electrical component comprises electrical leads and the board substrate comprises an electrically conducting surface. The method comprises positioning the electrical component proximate to the board substrate, applying a conductive adhesive for affixing the electrical component to the board substrate, aligning the electrical leads with corresponding locations on the electrically conducting surface, and urging the electrical component onto the board substrate. The conductive adhesive may include room temperature vulcanization (RTV), silver conducting RTV, silver conducting adhesive, silver conducting epoxy, gold conducting RTV, gold conducting adhesive, and gold conducting epoxy. The board substrate may be a printed circuit board, a hybrid module, and a multi-chip module. The electrical lead can include conducting pins and a ball grid array.  
      The electrical component considered for use with the present method and apparatus includes digital and analog integrated circuits, processors, micro-processors, downhole sensors, cooling components, antennas, receivers, resistors, inductive elements, capacitors, diodes, hybrids, multi-chip modules, all surface mount electronic components both passive (resistors and caps) and active (integrated circuits and op amps). The method may further include disposing the electrical component on the board substrate within a downhole tool. The downhole tool can be a perforator, a logging tool, a bond evaluation tool, a formation testing device, or a seismic acquisition device. The method can also include applying the conductive adhesive to the electrical component, to the board substrate, or both.  
      The present disclosure also includes a device comprising a board substrate, an electrical component, an electrical lead on the electrical component, and a conductive adhesive securingly formed between the electrical lead and the board substrate. The conductive adhesive included with the device may provide mechanical and electrical connectivity between the electrical component and the board substrate. The component for use with the present device may be a digital or analog integrated circuit, a processor, a micro-processor, a downhole sensor, a cooling component, an antenna, a receiver, a resistor, an inductive element, a capacitor, a diode, a hybrid module, a multi-chip module, all surface mount electronic components both passive (resistors and caps) and active (integrated circuits and op amps). The conductive adhesive may be temperature vulcanization (RTV), silver conducting RTV, silver conducting adhesive, silver conducting epoxy, gold conducting RTV, gold conducting adhesive, and gold conducting epoxy. The board substrate may be a printed circuit board a hybrid module, or a multi-chip module and the electrical leads may be conducting pins or a ball grid array. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING.  
       FIG. 1  is a partial cross-sectional view of a downhole tool within a wellbore.  
       FIG. 2  is a cross sectional view of a ball grid array.  
       FIGS. 3   a  and  3   b  are cut-away views of embodiments of a ball grid array connector system disclosed herein.  
       FIG. 4  is a side view of an embodiment of an electrical component attached to a board substrate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      One embodiment of the method and apparatus described herein involves using an electrically conductive adhesive to connect an electrical component to a board substrate thereby forming an electrical device. Implementation of an electrically conductive adhesive provides not only an electrical connection between the component and the substrate, but also serves to mechanically affix the device to the substrate. Moreover, the flexible nature of the adhesive compensates for any stresses and shock, such as by thermal expansion, and prevents cracking or dislodging of the component, which can occur in typical connection means.  
      With referenced now to  FIG. 3   a  one embodiment of a novel connection means is illustrated therein. Here, a portion of a ball grid array structure is shown connected to a circuit board. While only a single solder ball  18  is illustrated in  FIG. 3   a , it should be understood that the configuration illustrated is equally applicable to an entire BGA having a multiplicity of such solder balls  18 . Thus an entire BGA could be secured to a substrate by applying electrically conductive adhesive to each solder ball  18 , or to a selected number of solder balls  18  of an associated BGA. The solder ball  18  may operate as an electrical lead thereby allowing electrical signals to pass to and from the electrical component and the circuit board  22 . As shown, the solder ball  18  is affixed onto a circuit board  22  with an amount of an electrically conducting adhesive  24  having been applied between the solder ball  18  and the circuit board  22 . The adhesive for use with the present disclosure can include any conducting adhesive (including the conduction of electricity and/or thermal energy) and more specifically may comprise room temperature vulcanization (RTV), as well as metal based adhesives such as silver conducting RTV, silver conducting adhesive, silver conducting epoxy, gold conducting adhesive, and gold conducting epoxy.  
      The electrical component  19  of which the solder ball  18  is a part of can be any surface mounted electrical or electronic component, examples include an integrated circuit, a processor, a microprocessor, a downhole sensor, a cooling component, an antenna, a receiver, a resistor, an inductive element, a capacitor, diodes, and an operational amplifier. With regard to the circuit board  22  (also referred to herein as a board substrate), the circuit board  22  can be a printed circuit board, a hybrid board, a multi-chip module, and a connector.  
      With reference now to  FIG. 3  another embodiment is shown therein. In this embodiment the electrical device  19  comprises all the elements as shown in  FIG. 3   a  in addition to a conductor plate  20  that resides on the upper surface of the circuit board  22 . Optionally, it may be desired to have a conductor plate  20  on the circuit board  22  for making proper electrical communication on the surface of the circuit board  22  between other devices and/or components attached to the circuit board  22 . Optionally, electrically conductive traces, possibly comprised of a conducting metal such as copper, can be situated on internal layers of a board substrate, on the outside layers, or on both. In yet another embodiment of the apparatus method shown herein is illustrated in a side view in  FIG. 4 . Here an electrical component  26  is shown having pins  28  extending downward from its body through a circuit board  22   a . It is well understood, that the pins  28  comprise conducting an electrical signal to and from the electrical component  26  and the printed board  22   a . The pins  28  also comprise an electrical lead for electrical communication between the electrical device  26  and the circuit board  22   a . Apertures (not shown) are formed through the circuit board  22   a  to accommodate for the pins passing therethrough. Optionally the electrically conducting adhesive  24   a  can be applied along the outer surface of the pins where they intersect the circuit board  22   a . Inclusion of the electrically conductive adhesive can provide not only electrical communication between the electrical component  26  and the circuit board  22   a  but can also mechanically affix the electrical component  26  to the circuit board  22   a.    
      In operation one or more of the electrical components described above may be secured to a board substrate attaching the electrically conductive adhesive either to the electrical leads of the electrical components or onto the board substrate. In one application method, the conductive adhesive may be applied to the board substrate manually with a syringe. The adhesive may optionally be applied by the use of a surface mount assembly machine. To ensure a sound bond, the plating of the respective mating surfaces should be clean and free of non-conducting detritus. One enhancement of use could include plating these surfaces with a highly conductive substance such as platinum gold. Many adhesives, such as RTV, require several hours of curing time. This time may be reduced by applying heat or ultraviolet (UV) light to the adhesive. Conductive epoxy cure time may be reduced with heat also.  
      Among the many uses for the electrical device constructed in the method herein described, one includes inclusion of these devices and one or more of the downhole tools described herein. As previously discussed, the harsh and rigorous environment experienced by all components of downhole tools often can cause damage to currently known construction methods of such electrical components. Accordingly implementation of the electrically conducting adhesive as herein described provides one solution to the problems of cracks and disintegration of connections that are currently being experienced.  
      The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.