Cleaning and liquid contact with solids – Processes – With treating fluid motion
Reexamination Certificate
2001-03-21
2003-01-07
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
With treating fluid motion
C134S035000, C134S037000, C134S199000, C015S302000, C015S345000, C239S079000
Reexamination Certificate
active
06503336
ABSTRACT:
BACKGROUND OF THE INVENTION
Some circuit board manufacturers occasionally have the need to remove soldered lead frame integrated circuit (IC) components from circuit boards. For example, a circuit board manufacturer may have inadvertently manufactured a batch of circuit boards with the wrong, faulty or unreliable (e.g., “out of spec”) lead frame components. Rather than scrap the otherwise correctly manufactured circuit boards, the manufacturer unsolders the original lead frame components from the circuit boards, cleans the circuit boards, and subsequently solders new lead frame components to the circuit boards.
A typical lead frame component is rectangular in shape and has sets of metallic leads that extend on two sides (i.e., opposite sides), or alternatively on all four sides. After such a component has been soldered to a circuit board, a circuit board manufacturer can unsolder that component from the circuit board using a manifold assembly that blows heated gas (e.g., heated nitrogen gas) therethrough. To this end, a user (e.g., a trained technician employed by the circuit board manufacturer) typically places the circuit board on a flat heater so that the side of the circuit board having the lead frame component faces up. The flat heater raises the overall temperature of the circuit board (e.g., to a temperature of 100 degrees Celsius). The user then lowers the manifold assembly over (i.e., on top of) the lead frame component. The manifold assembly typically includes a set of metallic exhaust elements which extend from a central location down over the metallic leads of the lead frame component. Typically, the manifold assembly further includes a vacuum element which is disposed between the exhaust elements and which extends from the central location down on top of the package of the lead frame component. After the user lowers the manifold assembly over the lead frame component, the user activates (i) a vacuum source that sucks air through the vacuum element, and (ii) a heated gas source that blows heated gas through the exhaust elements. The exhaust elements of the manifold assembly direct the heated gas in a downward direction toward the circuit board surface and over the metallic leads of the component. Eventually, the heated gas melts the solder holding the metallic leads of the component thus freeing the component from the circuit board. The vacuum element takes hold of the lead frame component, and the user then lifts manifold assembly and the component (which is now attached thereto) away from the circuit board thus completing removal of the component.
In subsequent steps, the manufacturer cleans the circuit board and prepares the circuit board to receive a new lead frame component. To this end, the user typically removes (e.g., melts and vacuums) any remaining solder from the exposed mounting location of the circuit board (i.e., the circuit board location on which the original lead frame component resided), and washes the mounting location using a special solution that removes oxidized metal and any remaining contaminants.
Next, the user installs the new lead frame component on the mounting location of the original lead frame component. To this end, the user distributes, or “prints”, solder paste over the mounting location using a stencil. Next, the user positions the new lead frame component over the mounting location using a workstation having a microscope and a set of gears that enable the user to locate the new lead frame component over the mounting location with high precision. The user then applies heat to solder the new lead frame component in place. In some situations, the user can use the same flat heater and manifold assembly which were used to remove the original lead frame component (e.g., the flat heater and the manifold assembly can be integrated parts of the workstation). In other situations, the user employs other devices to solder the new lead frame component in place (e.g., automated equipment).
Some circuit board manufacturers can remove and install ball grid array (BGA) components using a metallic nozzle that blows heated gas over the BGA components in order to heat the BGA components in a top down manner. That is, the nozzle blows heated gas onto the top of the BGA component toward the surface of the circuit board. Accordingly, the temperature of the top of the BGA component gradually rises ahead of the temperature at the bottom of the BGA component, and eventually the heat permeates to the soldering region underneath the BGA component. Accordingly, the temperature of the soldering region of the BGA component (i.e., an array of solder balls) eventually exceeds the solder melting temperature and the BGA component becomes free. A central vacuum element in the middle of the nozzle grabs the BGA component in a manner similar to that for the lead frame devices so that the BGA component can be removed from the circuit board by lifting the nozzle away from the circuit board.
After the BGA component is removed, the mounting location of the circuit board can be cleaned of old solder and printed with new solder for installation of a new BGA component. Then, the user can install the new BGA component onto the mounting location. In some situations, the user can use a workstation that employs the same metallic nozzle which was used to remove the BGA component. In other situations, the user can employ automated equipment to install the new BGA component. A typical amount of time for the entire process of removing an old BGA component, cleaning and prepping the mounting location, and installing a new BGA component is approximately one hour.
SUMMARY OF THE INVENTION
Unfortunately, there are deficiencies to above-described conventional approaches to removing circuit board components. For example, it takes a significant amount of time to remove a BGA component from a circuit board and install a new one (e.g., one hour). In situations that require removal and replacement of such a component from many circuit boards (e.g., mass production situations), the component removal/installation station that performs the process of removing the old circuit board components and installing new circuit board components in their place can easily become a bottleneck.
Additionally, the process of installing a new BGA component using the above-described top down heating approach can provide significant stresses on the component and the mounting location of the circuit board. In particular, the uneven heating of the component and the mounting location for an extended period of time (i.e., raising the temperature of the top of the component ahead of the component underside and the mounting location of the circuit board) provides substantial thermal stresses that raise reliability concerns. That is, severe distortions (e.g., twisting and bending) in the component and in the circuit board can damage any of the interconnects between the silicon chip and the internal conductors of the circuit board, the circuit board laminate and/or the neighboring interfacial vias (e.g., fracturing a wire bond).
Furthermore, the above-described conventional manifold assembly, which has the exhaust elements and the vacuum element, is not well-suited for removing or installing a circuit board component having a solder region hidden between the component itself and the circuit board since the manifold assembly is typically lowered on top of an component, the exhaust elements of the manifold assembly typically blow heated gas toward in a downward direction toward the circuit board surface. The heated gas typically does not blow underneath the IC component but simply down on top of the metallic leads.
In contrast to the above-described conventional approaches to removing and installing circuit board components, the invention is directed to techniques for modifying a circuit board (e.g., removing and/or installing a circuit board component) by providing fluid (e.g., heat gas) between the circuit board component and the circuit board. As such, the temperature of the circuit board and the component can be contr
Chapin & Huang , L.L.C.
Chaudhry Saeed
EMC Corporation
Gulakowski Randy
Huang, Esq. David E.
LandOfFree
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