Abstract:
A decapsulation apparatus has an etch plate, an off-center etch head having an opening, a cover sealing to the etch plate forming an etching chamber, a gasket surrounding the opening, a ram sealed through the cover, a pressure-controlled source of Nitrogen or inert gas continuously purging the etching chamber at a low gas pressure, a f toggle mechanism mounted to a metal plate t, an etchant supply subsystem comprising sources of etchant solutions, an etchant solution pump, supply passages and controls to select etchants and etchant ratios, and a heat exchanger heating or cooling the etchant solution, etchant waste passages f conducting used etchant away. Etchants are mixed in the passages to the reaction region, and turbulence in the reaction region is promoted by impinging etchant solution on the encapsulated device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is in the field of semiconductor manufacturing and pertains more particularly to methods and apparatus for applying an etchant to decapsulate all or a portion of an encapsulated electronic device. 
         [0003]    2. Discussion of the State of the Art 
         [0004]    Plastic packaging of various electronic devices, including semiconductor chips, is a well-known process that has been practiced for a long time. Typically, an epoxy or other plastic resin is molded around a semiconductor device creating a chip package. The molding protects a central portion of a lead frame and bonding wires or other connections between contact pads on the chip or device to inner lead fingers on the lead frame. It is often required to decapsulate such a semiconductor package at least in part to allow for device inspection, device testing and, if needed, repair of the chip and or wire bonds to the chip and inner lead fingers after the encapsulation material) covering these elements is removed. 
         [0005]    Most commonly, concentrated acids such as sulfuric acid and fuming nitric acid and other liquid materials are used in the decapsulation process to etch the resin material. One challenge in decapsulation systems of prior art is controlling the exact amount of etchant injected into the process. Moreover, a related challenge is preventing damage to the package under process, including preventing damage to interior copper or other metal wires or metal components of the device. 
         [0006]    It is desired in some cases that devices which are already attached to a printed circuit board (PCB) or other substrate be decapsulated without removing the semiconductor device from the PCB or mounting substrate. Removing the solder may create additional defects. Additional operational artifacts can be confused with defects built into the device or defects resulting from mounting the device to the PCB or substrate. 
         [0007]    Prior art decapsulating systems are also limited in the size of device that can be mounted by the size of the etch plate and safety cover. Prior art systems have the etch plate or etch head centrally located. Therefore to accommodate, for example, a six inch square sample, the etch plate and cover must be over 12 inches square, lending to a system that is too large to handle the pressurization on the cover and etch plate. Some systems use an etch plate manufactured of virgin polytetrafluoroethylene (PTFE) and supported only on the periphery of the system. The higher pressure range may damage or deform the etch plate. 
         [0008]    Yet a further limitation of prior decapsulating systems is that due to triboelectric characteristics of the PTFE etch plate, high electrostatic discharge from the plate may occur during movement of the device from the plate and fixture. Furthermore, if the device is mounted to a PCB or substrate there is a possibility of electrostatic discharge (ESD) damage to PCB interconnects and the clamping apparatus holding the device cover down. 
         [0009]    Therefore, what is clearly needed is a decapsulation system that eliminates the problems described above. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In one embodiment of the invention a decapsulation apparatus is provided comprising an etch plate supporting substantially off-center an etch head having an opening for exposing a portion of an encapsulated device to etchant solution, a vertically translatable cover sealing to the etch plate, the etch plate and cover forming an etching chamber over the etch head, a gasket on the etch head surrounding the opening, the gasket for sealing an encapsulated device or a portion of a printed circuit board (PCB) supporting an encapsulated device to the etch head, exposing the encapsulated device through the opening to etchant solution, a ram mechanism sealed through the vertically-translatable cover, adapted to translate a ram downward to urge the encapsulated device or PCB against the gasket, a pressure-controlled source of Nitrogen or inert gas coupled into the etching chamber, continuously purging the etching chamber at a low gas pressure, a force-producing, locking toggle mechanism mounted to a metal plate to which the etch plate is also mounted and a top of the cover, the toggle mechanism adapted to exert a downward force on the cover, to keep the cover sealed against upward force exerted by the nitrogen supplied to the etch chamber, the mechanism releasable to open the cover, an etchant supply subsystem comprising one or more sources of etchant solutions, an etchant solution pump, supply passages to a reaction region adjacent the encapsulated device, and controls to select etchants and etchant ratios, a controlled heat exchanger through which the supply passages pass, heating or cooling the etchant solution transported to the enapsulated device, one or more etchant waste passages from the reaction region for conducting used etchant away from the encapsulated device, wherein etchants are mixed in the passages to the reaction region, and turbulence in the reaction region is promoted by impinging etchant solution on the encapsulated device. 
         [0011]    In one embodiment the controlled heat exchanger utilizes electric heaters and thermoelectric cooling elements to control temperature of the etchant mixture to temperatures between 0 degrees Celsius and 250 degrees Celsius. Also in one embodiment the etch plate is supported by both a metal plate to which the lift mechanism is mounted and a secondary metal support between the heat exchanger and etch plate so as to prevent deformation of the etch plate. Also in one embodiment the toggle mechanism for the safety cover comprises two synchronized lift arms operated by two independent toggle mechanisms. Also in one embodiment the two independent toggle mechanisms are synchronized by a single lever and link with a travel stop for the single lever. 
         [0012]    In one embodiment of the invention the single lever has its rotational motion reversed by a two gear mechanism. Also in one embodiment the two lift arms function as springs to maintain force on the safety cover. Also in one embodiment additional Bellville springs are used to augment the spring qualities of the lift arms Also in one embodiment continuously purging with nitrogen or other gas is accomplished by intermittently introducing high pressure dry nitrogen or other gas directly into the etching chamber. And in one embodiment the pressure is maintained in the etching chamber by introducing high pressure dry nitrogen or other gas when the pressure in the chamber is less than a pre-programmed level and terminating the introduction when the pressure in the chamber reaches a level somewhat greater that the preprogrammed level. 
         [0013]    In an alternative aspect of the invention a method for decapsulating is provided comprising the steps placing an encapsulated device or a printed circuit board including an encapsulated device on a gasket on an etch head supported substantially off-center on an etch plate, the etch head and gasket having an opening exposing the encapsulated device to a reaction region below the etch head, sealing a vertically-translatable cover to the etch plate with a toggle mechanism mounted to a metal plate to which the etch plate is mounted, the etch plate and cover forming an etching chamber over the etch head, urging the encapsulated device against the gasket by a ram mechanism operating sealed through the cover, continuously purging the etching chamber with a pressure-controlled source of Nitrogen or inert gas, delivering an etchant solution to the reaction region from a controlled pump drawing etchant solution in a preset ratio from one or more sources, heating or cooling the etchant solution in passages leading to the reaction region through a heat exchanger, and removing used etchant solution from the reaction region through one or more waste passages. 
         [0014]    In one embodiment of the method a portion of the etchant is oscillated out of and back into the reaction region, digesting resinous material on the encapsulated device to form a hole in the resinous material. Also in one embodiment the temperature of the etchant mix is controlled to be in a range of from 0 degrees Celsius to 250 degrees Celsius. Also in one embodiment multiple interlocking gaskets are used to seal the PCB or encapsulated device to the etch head. 
         [0015]    In one embodiment of the method the controlled pump draws etchant solution from two separate sources, one providing fuming sulphuric and the other fuming nitric acid, shear mixes the solution in the passages through the heat exchanger, and oscillates a portion of the mixture into and back out of and back into the reaction region. Also in one embodiment the ratio of nitric to sulphuric acid in the etchant solution is controlled, and the heat exchanger is controlled to maintain the temperature of the etchant solution above the known freezing temperature of the etchant solution at the ratio selected and controlled. Also in one embodiment the ratio of nitric to sulphuric acid in the etchant solution is controlled, and the heat exchanger is controlled to maintain the temperature of the etchant solution below the known boiling temperature of the etchant solution at the ratio selected and controlled. In one embodiment the ratio of nitric to sulphuric acid is controlled to be 0:1, 1:1, 2:1, 3:2, 3:1, 7:2, 4:1, 5:1, 6:1, 9:1, or 1:0. And in one embodiment multiple interlocking gaskets are used to seal the encapsulated device or PCB to the etch head, wherein each gasket has a rectangular recess that precisely fits the next higher gasket, each gasket is larger than the next higher gasket, and the top gasket has a recess that closely fits the encapsulated device or PCB. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]      FIG. 1  is a partial section view of a decapsulating system according to an embodiment of the invention. 
           [0017]      FIG. 2  is an overhead view of the etch plate of  FIG. 1  and supporting hardware. 
           [0018]      FIG. 3  is an overhead view of the decapsulator cover lifting and clamping assembly. 
           [0019]      FIG. 4  is an elevation view of the cover lifting assembly of  FIG. 3 . 
           [0020]      FIG. 5  is an elevation view of the linkage structure of the lifting assembly of  FIG. 3  in clamped and locked position. 
           [0021]      FIG. 6  is a plan view of the linkage of  FIG. 5  in an unclasped or unlocked position. 
           [0022]      FIG. 7  is a plan view of a PCB or substrate containing a mounted semiconductor device mounted for decapsulation on the device of  FIG. 1  in a multiple gasket configuration according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    In various embodiments described in enabling detail herein the inventor provides a unique system for decapsulating semiconductor devices including devices mounted to printed circuit boards or other substrates and with other components mounted. The present invention is described using the following examples, which may describe more than one relevant embodiment falling within the scope of the invention. 
         [0024]      FIG. 1  is a partial section view of a decapsulating system  100  according to an embodiment of the invention. Decapsulation system  100  includes an etchant delivery pump  101 . Pump  101  delivers one or a mix of decapsulation etchant into a decapsulator heat exchanger  119  via a delivery line  106 . Pump  101  includes a supply line  103  to an etchant source and a supply line 
         [0025]      105  to a different etchant source (etchant source containers not illustrated). Decapsulation system  100  includes an etch head  115  mounted (clamped in one implementation) to an etch plate  114 . Etch head  115  supports device mounting apparatus enabling mounting of a semiconductor device that is in turn mounted to a PCB or similar substrate. One such device is depicted herein as a semiconductor device or package  116 . Package  116  is an encapsulated package and may require decapsulation at least in part to reveal components for quality or lot control (QC) testing and repair if required. Etch head  115  may be clamped to heat exchanger  119  by a retainer ring  134 . Etch head  115  may be sealed to etch plate  114  via an O-ring seal. 
         [0026]    System  100  includes an etch chamber cover  108  that fits over etch plate  114  to create an etching chamber that can withstand high pressurization. Cover  108  may be locked or clamped down over etch plate  114  using a unique clamping apparatus that is described in detail later in this specification. Cover  108  is moveable and may be unclamped and lifted off etch plate  114  using the same apparatus described above for clamping the cover onto the etch plate. In this example package  116  rests on a gasket  129 . Cover  108  may be sealed to etch plate  114  using an O-ring seal  107 . 
         [0027]    When cover  108  is clamped in place over etch plate  114 , an etch chamber  130  is created. 
         [0028]    Etch head  115  may be clamped over a heat exchanger  119  in system  100 . Etch head  115  has a passage  135  adapted to deliver etchant and dispenses of waste etchant through two waste passageways  122 . Passages  135  and  122  extend into the heat exchanger with waste passages  122  extending out of the heat exchanger. System  100  includes a ram nose  132 . Ram nose  132  is driven toward device package  116  by a ram piston  111  against a ram  131  to which ram nose  132  is threaded. 
         [0029]    Pressure for driving the ram may be supplied by a pressurized source of gas, such as inert nitrogen gas. A valve mechanism  123  hosting two electrically operated valves  124  and  125  may be provided to meter pressurized nitrogen to pressure chamber  112 . Valve  124  may be operated to allow nitrogen gas to pass through a tube  113  fitted onto a passageway into the pressure chamber. Nitrogen gas may be used to pressurize chamber  112  to drive ram nose  132  against the device package sealing the device package to gasket  129  and etch head  115 . A ram return spring  110  is provided to withdraw ram nose  132  from the device package when pressure in chamber  112  is released. 
         [0030]    Ram piston  111  and ram  131  may be housed within a ram mount  133 . Cover  108  may be fixed or otherwise attached to a cover mount  109 . In one implementation, ram mount  133  includes a mounted optical position sensor (not illustrated) that may detect full extension of ram  132  and ram piston  111 . Valve plate  123  includes an electrically operated valve  125  that may allow passage of nitrogen from the same source through a tube  134  into the etch chamber  130  through etch plate  114  during purge operations. When valve  124  is not activated, the volume of chamber  112  and tube  113  may be vented to the environment. 
         [0031]    System  100  includes a pressure transducer  136  having connection to etch plate  114  via a fitted tube  121 . In operation, pressure within chamber  130  is monitored by transducer  136 . Pressure threshold measurements may be observed for both high pressure states and low pressure states. For example, if pressure within chamber  130  drops below a minimum threshold as measured by transducer  136 , the electronic controller or control system may open valve  125 . When the pressure in chamber  130  exceeds a certain pressure threshold value as measured by the transducer, the controller or control system may close valve  125 . In this way the pressure within chamber  130  may be managed to be within an expected range that is lower than the pressure of the source tank or container of nitrogen. 
         [0032]    Pump  101 , as described above, has an etchant delivery tube  106  leading from pump  101  into heat exchanger  119 . Tube  106  has a flanged end (not visible) that may be sealed via an P ring against etch head  115 . Tube  106  connects to the source delivery passage  135  in the heat exchanger, which in turn enters the etch head. Pump  101  draws etchant from supply containers through lines  103  and  105  and pumps the etchant into line  106  for delivery to the decapsulator. Tube  104  is a nitrogen purge line. When the etchant delivery is in heat exchanger  119 , it may assume a temperature similar to that of the heat exchanger. 
         [0033]    Heat exchanger  119  may be heated by one or more electrically-controlled heating devices  136  and may be cooled by a thermoelectric cooling assembly  120 . A control system may be used to monitor and to control or adjust the temperature of the heat exchanger. The desired temperature value may be below ambient temperature, as low as zero degrees Celsius (C.) for packages containing copper metallization. The temperature may also be maintained above the boiling points of the etchants, such as at two hundred and fifty degrees C. for packages not containing any copper metallization. 
         [0034]    Pump  101  may be controlled to select either one or the other enchant supply tubes  103  or  105  to activate etchant delivery at each delivery cycle. In this way pump  101  may deliver one etchant at a time or any ratio of mixed etchants. Etchant delivery cycles may be very rapid and under a relatively high pressure. Etchant mixes may therefore be made homogenous through shear mixing within tube  106  leading into heat exchanger  119 . Each fresh delivery of etchant during a decapsulation run agitates etchant already in contact with the etch cavity on the device being processed. Some portion of etchant in contact with the package may be displaced into the waste or passages  122  in etch head  115 . Passageways  122  extend from the etch cavity at the top of etch head  115  through the etch head, through heat exchanger  119 , through thermoelectric cooling device  120 , and through a waste junction block  128 . 
         [0035]    Pump  101  may be a diaphragm dispensing pump capable of delivering high velocity pulses of etchant to the etchant heat exchanger. Pump  101  has capability of pumping etchant from multiple sources on a cycle-by-cycle basis allowing for generation of various mix ratios of the etchants. The process in one embodiment uses fuming nitric acid, fuming or concentrated sulfuric acid, or a mixture of the two acids at a controlled temperature from the boiling point of the etchant or mixture down to below ambient temperatures. 
         [0036]    High velocity of the pulses produces shear mixing in the etchant heat exchanger and creates turbulence in the etch cavity formed on the package exterior surface by reaction of the etchant solution with the resinous material. This turbulence provides for removal of non-reactive elements of the encapsulating resin from the etch face resulting in exposure of more of the reactive material for faster etching. The pump is also capable of withdrawing etchant from the etch cavity to again deliver the etchant with high velocity pulses. This partial recycling of the etchant reduces etchant usage while maintaining delivery of high velocity pulses at a high rate. 
         [0037]    Waste passages  122  may be combined in waste junction block  128  into one stream transported through a waste tube  127 . Combined waste then travels through tube  127  and into a second heat exchanger  102  that returns the temperature of the heated waste back to near ambient temperature. O-ring seals provide connection sealing for the waste tubes  122  at the appropriate junctions with different components. Output from second heat exchanger  102  may lead to a waste container (not illustrated) adapted to store waste etchant materials. 
         [0038]    In one embodiment, etch plate  114  is manufactured of carbon filled-PTFE and is attached to a top plate (see  FIG. 2 ) by screws threaded into inserts (not illustrated) installed in etch plate  114 . The central area of the top plate may be relieved by machining to an extent so that heat exchanger  119  and thermoelectric device  120  may be directly affixed to etch head  115 . In a preferred embodiment, Etch head  115 , heat exchanger  119 , and thermoelectric assembly  120  may be assembled onto etch plate  114  and placed on the top plate as a single assembly. 
         [0039]    Etch plate  119  in one embodiment is made of carbon-filled PTFE making it stronger and more dimensionally stable than virgin PTFE. The etch plate is supported over most of its area and a separate reinforcing plate (top plate) is mounted to the bottom side to limit deformation. In addition the carbon-filled PTFE is conductive, eliminating static voltage generation. The clamping mechanism may be manufactured of conductive poly ether ether ketone (PEEK) eliminating discharges from the component to the clamping device, and may be connected to earth ground by contact with the ram return spring, the stainless steel ram mount, and through the cable earth connection to the cover mount. 
         [0040]    In one embodiment a support plate  117  is provided to minimize tendency for the etch plate to become warped or otherwise compromised due to high pressure in etch chamber  130  and the down force of ram nose  132  on device package  116 . Support plate  117  may be fixed or otherwise attached between heat exchanger  119  and etch plate  114 . Support plate  117  may be mounted to the etch plate  114  by screws threaded into inserts installed in the etch plate. In one embodiment PTFE spacers may be placed between heat exchanger  119  and support plate  117 . The larger area of cover mount plate  109  fairly distributes the downward force over a large area of cover  108  reducing deflection of the cover. 
         [0041]    It is noted herein that heat exchanger  119  may incorporate a serpentine of etchant-resistant tubing that is encased in an aluminum block. This aluminum block may also contain electric heaters and has contact with thermoelectric modules that can either heat or cool the aluminum block. An electronic control mechanism operates the heaters and thermoelectric modules to maintain a constant temperature of the aluminum block. The temperature can be controlled from well below ambient temperature that is, less than 15 degrees C., to well above the boiling point of the etchant, that is, more than 250 degrees C. 
         [0042]      FIG. 2  is an overhead view of the etch plate assembly of  FIG. 1  and supporting hardware. In this example support plate  117  is bolted to etch plate  114 . Etch plate  114  includes a passageway  203  within the etch plate leaving a portion unsupported. Support plate  117  provides added support for this portion. In this example a top plate  207  may also be provided to strengthen etching plate  114 . Etch head  115  is positioned offset from center on support plate  117 . Threaded inserts  204  are provided to enable attachment of etch plate  114  to top plate  207 . Threaded inserts  201  are provided to enable support plate  117  and heat exchanger ( 119   FIG. 1 ) to be attached to etch plate  114 . 
         [0043]    A peripheral groove  202  is provided in etch plate  114  and is adapted to seat a seal gasket, such as gasket  107  of  FIG. 1 , providing a seal for cover  108 . Etch plate  114  includes a threaded opening  205  and a threaded opening  206 . These openings facilitate attachment of tubes like tube  134  and tube  121 . In this example, the offset from center location of etch head  115  facilitates PCB-mounted devices up to six inches square with a smaller cover plate. Prior art systems are centrally oriented with respect to the etch head position requiring a much larger etch plate and safety cover of up to twelve inches square to accommodate devices of the same size (6 inches). The smaller footprint of the etching system in embodiments of the invention helps to reduce possible deformation and damage to the plate and cover under high pressure in the etch chamber. 
         [0044]      FIG. 3  is an overhead view of lifting and clamping assembly  300 . Assembly  300  includes a lever or lift arm  301 . Lift arm  301  may be manually operated to open and remove cover ( 108 ) or to clamp cover ( 108 ) to etch plate  114 . Lift arm  301  is fixed to a geared shaft or axle  302 . Axle  302  is housed within a bearing block  303  and a bearing block  306 . Axle  302  has a fixed gear  304 . Gear  304  is meshed with an adjacent fitted gear  305 . Gear  305  is fixed to a second shaft or axle  307 . Axle  307  is housed within bearing block  306 . 
         [0045]    Operation of lever arm  301  causes rotation of shaft  302  and concurrent gear interaction between meshed gears  304  and  305  to produce rotation of shaft or axle  307  in the opposite direction of the first rotation direction of shaft  302 . Assembly  300  includes a lever  313  that is affixed in this example to shaft or axle  307 . Mechanism  300  includes rotatable links  312  adapted to transmit the motion of lever  301  to two toggles (open, lock) made up of two links (not visible in this view) described further below. Mechanism  300  includes parallel cover arms  310  that are fixed to cover mount  316 , which may be analogous to mounting plate  109  of  FIG. 1 . Cover arms  310  are thinner at arm extensions  310 , which are mounted to cover mount. 
         [0046]    Lifting and clamping assembly  300  further includes support blocks  309 . Support blocks  309  are each adapted to support one cover arm  310  via a freely rotatable shaft or pin inserted through the cover arm and the support block. The cover arms may be freely rotatable at the inserted shaft or pin (not illustrated). The free ends of cover arms  310  are connected to the top of a cover mount  316  analogous to cover mount  109  of  FIG. 1 . 
         [0047]    In operation when lever arm  301  is moved, its motion may be transferred through meshed gears  304  and  305 , to lever  313 . Lever  313  acts through links  312  and  315  (toggles) to move pivotally-mounted cover arms  310 . It is noted herein that in this example all of the mechanism support architecture, such as cover arm supports  309  for example, are fixed to top plate  308 . The toggle operation runs in parallel with the toggles (links  311  and  315 ) locking to close the cover over the etch plate or unlocking to raise the cover up and away from the etch plate. Plate  308  includes a fixed travel stop  314  that may prevent excess range of motion for lever  313 . 
         [0048]    In one example lifting upward on lever or lift arm  301  may cause the cover mount to rise, raising the cover up and off of the etch plate typically after a process is complete and a purging operation has been performed. Cover arms  310  supply the downward force required to hold safety cover ( 108 ) in place against the etch plate or top plate. The large footprint of the cover mount compared to the cover results in distribution of force over a large area of the safety cover ( 108 ) reducing any deflection occurring during clamp down (locked) toggle state. 
         [0049]      FIG. 4  is an elevation view of the cover lifting assembly of  FIG. 3 . Some of the components depicted in  FIG. 3  are not visible in this view. As described previously, all hardware may be supported by top plate  207 . A travel stop  314  is provided in one embodiment and mounted to top plate  207 . Travel stop  314  limits the pivotal motion range of the pivoting safety cover ( 108 ). 
         [0050]    Top plate  207  shows a support block  412  that hosts a pair of links ( 414 ) and ( 312 ) that are pivotally connected and are used to drive a toggle pair of links  311  and  409 . One end of link  414  is be mounted to the rear side of support plate  412 . Link  312  may be an intermediary link connected at one end to lever link  414 , Link  414  has a fixed connection to a shaft ( 307 ) operated by a lift arm like lift arm  301 . The motion of the lift arm causes the shaft to move, resulting in movement of link  414 . Link  414  has a rotatable connection to intermediary link  312 . Link  312  has a rotatable connection to a pair of (toggle) links including a link  312  and a link  409 . Toggle links  311  and  409  form a toggle at certain positions, toggle referring herein to a switch like state for the chamber cover  108 . 
         [0051]    In this example, toggle links  311  and  409  are vertically aligned, signifying that cover  108  is down and locked. The other of two toggle states are “unlocked” or “unclamped”. Links  409  and  311  are rotatably connected together. Link  411  is rotatably connected to a toggle support block  411  on the end opposite of link  311 . Link  311  has a rotatable connection to cover arm  310 . Cover arm  310  has a thinner extension  317  (cross hatched). The end of cover arm extension  317  may be fixed to cover mount  109  via a tension screw  404  and a “Bellville” disc spring  403 . 
         [0052]    In this clamped position safety cover  108  is forced into contact with etch plate ( 114 ,  FIG. 1 ) compressing seal  107  ( FIG. 1 ) resulting in a substantially gas tight seal between the cover and etch plate. In one implementation a minimum pressure for the etch chamber may be approximately 2 pound per square inch (2 PSI). When the etch chamber  34  ( FIG. 1 ) is pressurized with minimally 2 PSI, the upward force on the safety cover is nominally 150 lb (68 Kg). At the minimum of 2 PSI, the nominal upward force on safety cover  108  is about 150 pounds. In addition, downward force of the ram body ( 110 ,  FIG. 1 ) pushes the ram nose ( 132 ,  FIG. 1 ) into contact with the semiconductor device to be decapsulated. This downward force results in an equal and opposite upward force on exerted on safety cover  108 . The total nominal upward force on the cover is about 162 lbs. in this circumstance. 
         [0053]    The downward force translated to cover mount  109  by cover arms  310  is greater than the upward combined force of 162 pounds. The downward closing force transmitted by the two cover arms is nominally 180 pounds, which is greater than the upward force on the safety cover plus the down force required to establish a seal between etch plate  114  and safety cover  108 . As described further above the toggle links  311  and  409  are used to clamp the cover down and force up the rear end of the cover arms in parallel. 
         [0054]    Cover arms  310  are pivotally mounted on cover arm support block  309 . The applied force results in some deflection of the cover arms  310  along the thinner extensions  317 . In addition there are in one embodiment several Bellville disc springs  403  located at the mounting site of each of the arms with the cover mounting plate. A shoulder screw  404  may be provided to loosely mount cover  108  via cover mount  109  to the cover arms ( 310 ). In this way safety cover  108  may freely move or deflect while downward pressure is applied. Such movement helps to get better sealing results against the etch plate. 
         [0055]      FIG. 5  is an elevation view of the linkage structure of the lifting assembly of  FIG. 3  in clamped and locked position.  FIG. 6  is an elevation view of the linkage of  FIG. 5  in an unclamped position. 
         [0056]    Referring now to  FIG. 5 , toggle links  311  and  409  are vertically aligned as described for a clamped or locked position where the safety cover is closed over the etch plate. Link  313  functions as a lever being fixed at one end to a shaft extending through support block  412 . Rotation of the shaft in a counter clockwise direction as viewed from this perspective forces intermediate link  312  to pull at the junction point shared with toggle links  311  and  409  resulting in a forced alignment of the toggle links vertically. 
         [0057]    It is noted herein that each toggle link is manufactured to be over a specific dimension from center line to center line of the toggle openings or the functional length dimension of each link. In this way the links lock, putting downward pressure on the safety cover through the cover arm extensions. In one implementation a magnet  516  is provided and disposed at a strategic location on top plate  207 . A second magnet  517  may be provided at a strategic location on toggle link  409 . When the link apparatus is in the locked or clamped position as depicted in this example, the magnets  516  and  517  are held separate from one another. The pivot point for cover arm  310  is at attachment block  309  where the pivot pin is mounted through the cover arm. 
         [0058]    Referring now to  FIG. 6 , toggle links  311  and  409  have been urged out of a vertically-aligned position associated with a closed and sealed safety cover. Reverse direction of motion applied to a lift arm ( 301 ,  FIG. 3 ) functions to break the link alignment by pushing toggle links  311  and  409  with lever-driven intermediate link  312 . The result is lifting of the safety cover via pivoting of cover arm  310  about the pivot point. 
         [0059]    When the mechanism is brought to the full cover-open position, magnet  517  on toggle link  409  makes contact with magnet  516  mounted on top plate  207 . The magnetic attraction between the magnets keeps the safety cover in the full open (pivoted) position. Referring now to  FIG. 3 , travel stop  314  includes an adjustable contact mechanism that may make physical contact with lever (fixed shaft link)  313  when the mechanism is in the locked down position of  FIG. 5 . 
         [0060]    Referring again to  FIG. 3 , the amount of force exerted on lift arm  301  to close and seal the safety cover over the etch plate ( 114 ,  FIG. 1 ) may vary considerably depending upon the position of the lift arm along the rotational path. The amount of force required to move the lift arm increases proportionally with the position of the arm along the rotational path such that the maximum required force on the lift arm occurs when the toggle links ( 311 , and  409 ), lever  313  and intermediate link  312  are at full extension. The manufactured lengths of the links and lever function to set the desired force ratio. 
         [0061]    In this example, a maximum extension force of 9 pounds is required to produce the approximate 180 pound downward force one the cover mount and cover through the extensions of the cover arms. By controlling the dimensional tolerances of the links with respect to functional length (center line to center line of link openings and the link connecting hardware (openings and pins), the desired force downward force for the locking mechanism may be configured. 
         [0062]      FIG. 7  is a sectioned elevation view of a PCB or substrate hosting a mounted semiconductor device for decapsulation on the apparatus of  FIG. 1  in a multiple gasket configuration according to an embodiment of the present invention. In this example a PCB  701  has a semiconductor device  702  mounted thereon. PCB  701  also includes at least one other component  706  mounted thereon. The additional component or components mounted to the PCB require that the PCB not be positioned too close to the etch head so as not to disturb that component or components. 
         [0063]    Semiconductor device  702  may be soldered to PCB  701  along with other components such as component  706 . In this example the presence of the additional components requires that the device be a certain larger distance from etch head  115 . To create a larger distance between etch head  115  and device  702 , gasket stacking is employed in one embodiment. In this embodiment there are three gaskets. A gasket  705  is positioned on etch head  115 . A second gasket  704  is positioned over gasket  705 . 
         [0064]    A physical feature or depression on gasket  705  enables gasket  704  to be centered over and fitted onto gasket  705 . A third and top gasket  703  fits into a physical feature on the top surface of gasket  704 . The physical features on the gasket surfaces may be molded pockets designed and of a size to fit another specific gasket. On the top surface of gasket  703 , a physical feature or pocket is provided to accept device  702 . 
         [0065]    In one implementation the stack of gaskets may include several gaskets stacked on top of one another. With for example 8 gaskets of typical thickness, the added distance between the etch head and device may be four tenths of an inch or so (approximately 10 mm). In an implementation using multiple stacked gaskets, each of the gaskets used in the application require a central opening the size of the decapsulation window or area on the device to prevent any part of a gasket obstructing the flow of etchant during the decapsulation process. 
         [0066]    It will be apparent to one with skill in the art that the decapsulation apparatus of the invention may be provided using some or all of the mentioned features and components without departing from the spirit and scope of the present invention. It will also be apparent to the skilled artisan that the embodiments described above are specific examples of a single broader invention that may have greater scope than any of the singular descriptions taught. There may be many alterations made in the descriptions without departing from the spirit and scope of the present invention. 
         [0067]    It will be apparent to the skilled person that the arrangement of elements and functionality for the invention is described in different embodiments in which each is exemplary of an implementation of the invention. These exemplary descriptions do not preclude other implementations and use cases not described in detail. The elements and functions may vary, as there are a variety of ways the hardware may be implemented and in which the software may be provided within the scope of the invention. The invention is limited only by the breadth of the claims below.