|Publication number||US3731377 A|
|Publication date||May 8, 1973|
|Filing date||Aug 19, 1971|
|Priority date||Aug 19, 1971|
|Publication number||US 3731377 A, US 3731377A, US-A-3731377, US3731377 A, US3731377A|
|Original Assignee||Muckelroy W|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Referenced by (13), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 1 Muckelroy 1 1 May 8, 1973  METHOD FOR HANDLING BEAM- LEAD AND ODD-SHAPED SEMI- CONDUCTOR DEVICES  Inventor: William L. Muckelroy, PO. Box
9685, Washington, D.C. 20016  Filed: Aug. 19, 1971  Appl. No.: 173,186
 US. Cl. ..29/626, 29/471.1, 29/493,
29/628, 117/235, 294/655  Int. Cl ..H05k 3/30  Field of Search ..294/65.5; 117/8,
117/239, 235; 29/47l.l, 624, 626, 628, 493, 589, 590', 214/1 ET, 1 BH, 1 EV Primary Examiner-Richard Bernard Lazarus Att0rneyHarry M. Saragovitz et al.
 ABSTRACT An apparatus and method for manipulating monolithic microelectronic dice are provided. The apparatus comprises a probe-like electromagnet which uses a variety of different shaped tips to change the configuration of the magnetic field. The magnetic field at the tip is further adjusted by reversing the polarity of the electricity in the electromagnet windings and controlling the power applied to these windings. The core of the electromagnet is maintained in a demagnetized state by switching the electrical polarity of the windings. The method comprises the steps of applying a magnetically permeable substance to the dice, attaching each of the dice to the electromagnet using the force of the magnetic field, moving the attached die to a preferred location and orientation and releasing said die. Said magnetically permeable substance may comprise a fluid adhesive with a magnetically permeable insulated powder mixed therein, a permeable metal formed in beam-leads, or a permeable metal formed into bumps on the surface of flip-chips.
13 Claims, 7 Drawing Figures Mm MA NEM LOW MAGNETC u hi gfi virghi ii MNYEYZlAL ADHESWE ADHESVE wna ADHESNE \NTO D\'5PENSER ONTO i WARM DRY LOCATET one ,7 ADHESNE ADHESWE woYZK STA'HON 2 PLACE TOOL ENERGZE wi i m r iacueo NEXT TO A we ELECTROMAGNEY To oe osn m5 33553 BY SSEE ENERGVLED TOOL R NEAR me PATENTEU HAY 8W5 SHEET 1 0F 3 APPLY MAsNemcomm me euerzcaxze ALLY PERMEABLE WWH ELECTROMAGNET SUBSTANCE ELECTROMAGNET W RELOCATE resouge POWER ELECTROMAGNET ms ause M\C Mm MAGNEUC Lem meuenc DROP OF MAGNEQC MATEWAL Aoweswe \NTO msPENsEYa ADHESNE ONTO D\CE.
LOCATE one WARM DRY m mueswe ADHESNE WORK STA'HON MOVE TOOL PLACE TODL ENERGLZE \NH'H mE mmcnen NEXT TO A me ELECTROMAGNEY To gm: w
DEPOSLT BL gwgg g BY REDUQNG ENERGVLED TOOL POWER NEMZ ms //VVE/V70Z, M1 041% Z, Mac/(54 K0) ZLM 51W i KAZQW p [M PATENTEDHAY 8 I973 sum 3 3 /'LOO flo ELECTRO- \00 my OOL l I \"LO c TO AC \INZWBLE I; Q 7 CONVERTER TRANSFORMER J owerz MAL/4M1. MUf Y 104/ SOUYZCE METHOD FOR HANDLING BEAM-LEAD AND ODD-SHAPED SEMI-CONDUCTOR DEVICES RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured, used, and licensed by or for the United States Government for governmental purposes without the payment to the inventor of any royalty thereon.
BACKGROUND OF THE INVENTION This invention relates generally to the assembly of microelectronic circuitry using substrates as bases onto which various types of components in the form factor of a die are mounted. Specifically this invention relates to a magnetic handling apparatus and method for manipulation of all types of die involved in the assembly microelectronic circuitry.
Among the many types of die to which this invention may be applied are eutectic monolithic chips, flipchips, leadless-inverted-devices (LlDs), beam-leaded devices, and monolithic ceramic capacitors, monolithic resistors, and monolithic inductors. The invention is particularly applicable to beam-leaded devices for these are not cubic as the other types of dice. Instead, they have beveled or truncated edges which makes this type of dice extremely difficult to handle by tweezers or any other means by which the sides are mechanically clamped.
Heretofore microelectronic dice were handled and manipulated by two primary means of applying force. The first of these means where tweezers. Tweezers were used to clasp and manipulate all types of die. The other method and apparatus of the prior art involved the use of vacuum supplied to an orifice in a pointed tool. The vacuum supplied the force necessary to attach the die to the tool and thereby permit manipulation. This means of manipulating microelectronic dice is not discriminatory and therefore other objects and debris in the vicinity of the die to be manipulated 'may also be sucked into the orifice. These orifices are usually less than mils in diameter and are easily clogged. The tips for these tools, because of the small orifice required, are quite expensive. Furthermore, if debris is sucked to the tip at the same instance as the die, contamination of the die as well as the tip may result. Moreover, further difficulty is experienced with this method in controlling the amount of force to be applied to the die. One way is to control the power to the vacuum pump supplying vacuum to the orifice. However, this is not wise because vacuum pumps are not designed for operation at lower than rated power levels and such operation may result in irrepairable damage. Another way is to control the size of the air passage or orifice. This is a cumbersome and impractical solution for the size of the orifice would have to be increased or a vent connected to the passageway in order to diminish the suction force. Thus, many inherent disadvantages exist in the early methods and apparatus of this art.
The invention described herein overcomes all of the disadvantages of the foregoing methods.
It is an object of this invention to provide a new and novel method for manipulating monolithic microelectronic die and a new apparatus for efiecting same.
It is yet another object of this invention to provlde a new and novel-apparatus and method for manipulating monolithic microelectronic dice which utilizes magnetic fields as a means of attachment.
It is yet an additional object of this invention to provide a new and novel apparatus and method for manipulating monolithic microelectronic dice which involves the application of a magnetically permeable substance to a surface of said die, said substance being compatible with the normal cleaning operations to which the assembled substrate is subjected.
It is still an additional object of this invention to provide a new and novel apparatus and method for manipulating monolithic microelectronic die wherein said substance may be removed in the cleaning operation of the assembled substrate by flushing with a solvent.
Yet another additional object of this invention is to provide a new and novel apparatus and method for manipulating monolithic microelectronic dice wherein the force means used to attach and move said die is completely variable between prescribed limits.
Still an additional object of this invention is to provide a new and novel apparatus and method for manipulating monolithic microelectronic dice wherein the manipulating tool comprises a plurality of interchangeable tips for changing the shape of the magnetic field.
These and other objects of the present invention will become more fully apparent with reference to the following specification and drawings which relate to several variations of a preferred embodiment of the present invention.
SUMMARY In accordance with this invention a new and novel apparatus and method for manipulating monolithic microelectronic dice utilizing the force of a magnetic field for attachment of said die is provided which descriminates in the application of the attachment force, against all non-magnetic contaminants and debris in the vicinity of said die. The method is based on the use of a probe-like tool comprising an electromagnet and propagating a magnetic field from its tip, a magnetically permeable substance applied to a surface of the die, and means for controlling and varying the force of the magnetic field from said tool. The method comprises the steps of applying a magnetically permeable substance to a surface of a monolithic microelectronic die, contacting said die with the attracting tip of said tool such that when a magnetic field is generated at the tip, the field produces sufficientforce to cause the die to adhere thereto, moving the tool with the die attached to it to a location and decreasing the magnetic field such that the die is released from the pole. In this method the magnetic field force at the tip is adjusted by reversing the polarity of the electricity in the windings and controlling the amount of electric power applied to the windings. In addition the core of the electromagnet is maintained in a demagnetized state by reversing the electrical polarity of the windings periodically and applying and controlling the appropriate amount of electrical power to the windings to accomplish this objective.
BRIEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof will clearly appear from the following description and from the accompanying drawings, in which:
FIG. 1a is a flow chart of the method for manipulating microelectronic monolithic dice.
FIG. lb is a flow chart of a method for manipulating microelectronic monolithic dice using a liquid magnetic adhesive. 7
FIG. 2 is a cross-section of the manipulating tool.
FIG. 3a is a drawing of a cylindrical electrical contactor.
FIG. 3b is a drawing of the strip electrical contactor in the plastic housing.
FIG. 4 is a perspective drawing of the strip electric contactor.
FIG. 5 is a block diagram of the electrical operation of the manipulating apparatus.
DESCRIPTION OF THE PREF ERRED EMBODIMENTS The method of the present invention will be easily understood in its broad aspects by reference to FIG. la wherein there is shown a flow diagram of the steps thereof. First a magnetically permeable substance is applied to the surface of a die in a particular die matrix. In the next step, the coated die is contacted with the tip of a tool comprising an electromagnet, said tool being illustrated in FIG. 2. Once the die is contacted by the manipulating tool the core of the electromagnet is energized by supplying electricity to the windings in the required amount necessary to generate sufficient force at the tip to hold said die to said tool. Once the force necessary to attach the die to the tool is attained the die may then be relocated to the bonding site or other site necessary to perform an assembly operation upon the die. Once relocated the die is detached by diminishing the power to the electromagnet windings. This is done by adjusting a power transformer 203 (See FIG. 5) connected to the windings of the tool. The above steps are considered essential to the application of this method for manipulation of microelectronic monolithic dice.
In particular, one type of magnetic substance may comprise a polyvinyl chloride adhesive with a magnetically permeable insulated powder mixed therein. The adhesive should have similar properties with reference to solubility as that of polyvinyl chloride glue. In order to insure compatibility with production cleaning methods used in the manufacture of hybrid microelectronic circuitry the adhesive must at least be soluble in acetone, trichloroethylene, or ketone. This type composition of the magnetically permeable substance permits removal of the substance once manipulation is no longer necessary and the die has been permanently attached to the substrate. A magnetically permeable insulated powder such as 2-81 permalloy is best because this insures against electrical shorting of the microminiature conductive paths on the substrate by a conglomeration and adherence of several of the magnetically permeable powder granules used in the composition. This may occur due to insufficient flushing and cleansing of the substrate after attachment operations are completed. In other words, the magnetic powder may form an electrical bridge from one microminiature conductive path to another. Magnetically permeable powder is described and specified in the referable art. It is to be understood that the magnetically permeable substance described herein is not to be limited to this particular composition and may consist of other forms of matter such as thin films of magnetically permeable metals or poly-crystalline coatings. It is also to be understood that magnetically permeable material may be deposited by several means and is not to be limited by the method described herein.
Turning to FIG. 1b, the magnetic material is loaded into a dispensing means comprising, for example, a syringe and hypodermic needle. The dispensing means is used to place a microdrop of the magnetically permeable material onto the top surface of the monolithic microelectronic die. The material is dispensed onto each of the die in a particular matrix as it is received from the manufacturer in the manufacturers package. Once the microdrops of material are deposited, the matrix is either placed in an oven or exposed to infrared heat lamps. This step serves to warm the mixture and cause the drop to spread over the top surface of the die forming a smooth even coating of the material. Once coated the adhesive is permitted to dry. Note that only one face of the die is coated and that face is the face opposite the face to be juxtaposed to the substrate and on which the die is resting. After drying, the matrix of dice is located at the work station at which the die are needed. Once this is done the manipulating tool is placed in the vicinity of one of the die to be picked up and removed to a bonding location, or to be picked up and bonded using the manipulating tool.
Referring to FIG. 2 the manipulating tool 200 comprises an electromagnet in the shape of a pencil structure with a means for energizing the windings of the electromagnet placed or incorporated into the tool itself. This-energizing means is a normally open switch which may be actuated by depression of button 110 with one or more fingers of the hand. To continue the method, the electromagnet in the manipulating tool is energized and the resultant field produced at the tip of the tool causes the magnetic material in the coating on the top of the die to be attracted and attached to said tip 85. The force of attraction is controlled by a variable transformer 203 which controls the power to -the windings of the electromagnet housed in the manipulating tool (See FIG. 5). The tool with the die attached is then moved to the bonding site for the die. Either the tool may act, in addition, as a bonding means or the die may be transferred to location such that a bonding tool contacts said die at that location and applies energy to the die in such a manner that is becomes attached to metalization or other electrical conducting means incorporated onto a substrate at that location. Alternately, the die may be maintained at the location of said tip of the manipulating tool and the manipulating tool used as a means for transferring energy to the die, such energy being sufficient to cause the die to become rigidly attached at the bonding site. These steps may be effected and accomplished by numerical controlled machinery without human intervention. Once the die is attached by the manipulating tool the force of the magnetic field is diminished or reduced prior to withdrawal of the tool from the die. This step may also be incorporated into the logic circuitry of a numerically controlled bonding apparatus.
In some cases, such as in the production of a laboratory prototype model of a hybrid circuit, it is desirable to relocate a particular monolithic microelectronic die to a substrate site and at that time to cause the die to move to another location. This is accomplished by reducing the magnetic field generated at the tip of the tool and locating said tool underneath the substrate and moving said tool along the underside of the substrate in the vicinity of the monolithic die thus causing the die to assume a similar movement along a similar path. In this manner, minute movements of microelectronic die may be obtained in order to get precise positioning of said die.
Turning again now to FIG. 2, there is shown a crosssection of the manipulating tool required in the method. The tool is essentially the same size as that of a hand held pencil-like soldering iron. The manipulating tool comprises a plastic cylindrical hollow member 95, said member having openings, 84 and 83, at both ends thereof, said member having an opening 92 on the side thereof, and said member having threads 94 in the opening 93 at one end thereof (See FIG. 3b). Returning to FIG. 2, opening 92 in the side of said plastic member 95 is provided to accommodate a switching means for supplying electricity to said manipulating tool. Core 80 is inserted through opening 84 at one end of said housing 95 and is held rigidly by mound 82, in said housing 95. Said core 80 is cylindrical in shape and is inserted through the unthreaded opening 84 of plastic housing 95. The last one-half inch of the core 80 at the unthreaded end of the plastic housing 95 has a diameter approximately twice that of the remainder of said cylindrical core. This last one-half inch has a hole 90 which is threaded and centered along the axis of the core 80. This threaded portion is for the insertion of a permeable magnetic tip 85 the inserted portion of which is threaded and screwed into the hole 90 in said core 80. The greater diameter at the end of the core rests upon circular mound 82 formed into the plastic housing 95. This mound 82 forms an interference for the larger diameter portion of the core thus preventing said core from being pushed completely through the inner space of the housing 95. Around said core is a plurality of conductive windings 60. One of the terminations of the conductive windings 60 is connected to screw 125. This screw 125 is in turn connected to strip contactor member 100 (See FIG. 4) which extends in a groove 181 (See FIG. 3b) approximately /5 of an inch in width down an inner side of the plastic housing chamber 95 to an opening 92 at the side of the housing 95. Returning to FIG. 2, the second contactor member is in the form of a cylinder (See FIG 3a). Second contactor member 65 comprises a conductive metal 75 embedded in a plastic material 65 shaped in the form of a cylinder with a lip 78 at one end thereof, threads 56 being formed at the outer periphery of said lip 78. The conductive cylinder 75 extends beyond the plastic material in 'which it is embedded at the unthreaded end thereof. Returning to FIG. 2, this portion of the conductive cylinder 75 which is exposed is inserted into the inner chamber of plastic housing 95 and screwed in threaded hole 55 until the unexposed portion of said conductive cylinder 75 is opposite the end of first contactor member 1100. Returning to FIG. 3a, a tab 79 of conductive cylinder extends up and beyond the lip 78 of the plastic coating 65 on said conductive cylinder 75. This tab 79 is approximately A; inch by 56 inch and is bent onto the upper surface of the lip 78 of said member 15. Said tab 79 further comprises a hole 76 and under said hole is a threaded hole 50 (See FIG. 2). The second termination of the conductive windings is attached to a screw 51 inserted into hole 50 and said screw 51 serves as a binding post in order to connect a power lead 18 from an outside source. Screw 125 connected to contactor member serves as a binding post for power lead 17. The small diameter end of said core is held rigidly in place by means of a screw 40 inserted through cap 45 and fastened into the end of said core 80. Another hole 42 in housing cap 45 serves as a inlet through which power cord 130 is inserted. Returning to FIG. 3a, plastic contactor 15 has a notch 77 therein such that when it is screwed into hole 55 said notch 77 is positioned directly above contactor 100 permitting screw 125 to be inserted into the hole 64 below the tab 66 of said contactor 100. Contactor 100 is pressed against contactor conductor portion 75 by means of a button 110 attached to contactor 100 and inserted through an opening 92 in the side of housing 95. The contact is designed to remain normally open by means of a spring and washer assembly, 115 and 105, respectively. The button 1 10 is cylindrical in shape and comprises two diameters, one diameter approximately three times that of the second diameter, the smaller diameter of which has inserted and formed into it, a screw 120. screw 120 is attached to first contactor means 100. Washer fits firmly around the smaller diameter of button 100 and between the washer and the larger diameter of button is inserted spring 115. The force exerted by spring against button 1 10 and washer 105 serves to force contactor 100 away from exposed cylindrical contactor 75.
A permanently polarized magnetic material may be demagnetized by immersion in a rapidly reversing magnetic field. Therefore, when the tip of the manipulating tool herein indicates a degree of magnetic polarization this may be eliminated by rapidly switching the polarity of the electricity supplied to the windings around the core of said tool. Referring to FIG. 5, the manipulating tool leads are connected to a polarity switch 201 which in turn is connected to a AC to DC converter 202 which in turn is connected in series to a variable alternating transformer 203 and the variable alternating transformer is connected to an alternating current power source 204. By switching the polarity switch 201 the polarity of the magnetic field in the core manipulating tool 200 may be reversed. By varying the setting of the transformer 203 value, the intensity of the magnetic field at the tip of the manipulating tool 200 may be controlled. By switching the polarity switch 201 several times and setting the variable alternating transformer 203 to the proper level any permanent polarization in the tip of the manipulating tool 200 may be eliminated. This ensures that the tool only attaches die when the button switch 110 on the side of the manipulating tool is depressed.
Another useful embodiment and operation system for the manipulating tool is to use a plastic material with a diarnagnetic material embedded in said plastic material as a core. in this combination the windings around said core may be polarized in a direction opposite to that of diamagnetic material. Knowing that a diamagnetic material repels magnetically permeable materials such as applied to the surfaces of the die, by increasing the field strength of the windings to the value that exactly opposes the value of the magnetic field permanently in the core and at the tip and then minutely adjust the value of the field of the windings, the tip may be made either to repel or attract a die coated with said substance.
Referring again to the magnetic permeable substance, this material may be applied during the regular processing steps for this particular type of die. That is, the bumps on the exit termination flip-chip dice may be formed using a magnetically permeable material instead of applying the material after all of the processing steps are terminated. The magnetically permeable substance may also be used in the formation of beam-leads during their normal formation process. Furthermore, in the case of leadless-inverted-devices (LIDs) a permanent layer of permeable magnetic material may be placed on the under side or top side of the ceramic carrier by vacuum deposition, silk screening, or other means available in the art of hybrid microelectronics. In consideration of the foregoing the manipulating tool used to handle beam-lead, flip-chip, or LID devices may also be used to apply energy to these die to accomplish permanent bonding of the die to the intended substrate.
It is to be understood that the inventor does not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.
What is claimed is:
1. A method for manipulating monolithic microelectronic die comprising the steps of a. applying a magnetically permeable and electrically insulated powder substance to a surface of a monolithic microelectronic die said surface having exposed electrical terminals;
b. contacting said die with the attracting pole of an electromagnet such that when a magnetic field is generated at said pole, said field produces sufficient force to cause said die to adhere thereto;
c. moving said electromagnet with said die attached thereto to a location and decreasing said magnetic field such that said die is released from said pole.
2. A method according to claim 1 further comprising the step of subjecting said magnetically permeable substance to an elevated temperature for a time period sufficient to cause said substance to spread over said surface.
3. A method according to claim 1 further comprising the step of demagnetizing said electromagnet by reversing the electrical polarity of said windings and controlling the electrical power to said windings.
4. A method according to claim 1 further comprising the step of adjusting the magnetic field strength at said pole by reversing the electrical polarity of said windings and controlling the amount of electrical power supplied to said windings.
5. A method for manipulating monolithic microelectronic die comprising the 5. of
a. applying a magnetically permeable substance to a surface of a monolithic microelectronic die' b. contacting said die with the attracting pole of an electromagnet such that when a magnetic field is generated at said pole, said field produces sufficient force to cause said dice to adhere thereto;
c. moving said electromagnet with said die attached thereto to a location and decreasing said magnetic field such that said die is released from said pole; and
d. removing said substance from said surface of said die by flushing with a solvent, said die having been attached to microcircuit, substrate prior to this step.
6. A method according to claim 5 further comprising the step of dissolving said substance with a solvent prior to flushing said die with a solvent said die having been attached to a microcircuit substrate prior to these steps.
7. A method according to claim 2 wherein said substance is a mixture which further comprises a solidifiable adhesive fluid.
8. A method according to claim 6 wherein said electromagnet comprises a probe having a magnetically permeable core, a tip protruding from one end thereof, a plurality of conductive windings located around said core, means for supplying electric current to said windings, and means for housing said core.
9. A method according to claim 8 wherein said core comprises a paramagnetic material and a ferrimagnetic material.
10. A method according to claim 8 wherein said core comprises a diamagnetic material and a plastic.
11. A method according to claim 1 wherein said location is at least one bonding pad on a microcircuit substrate to which said die is interjoined.
12. A method according to claim 1 wherein said location is a plurality of bonding pads on a microcircuit substrate to which the electrical exits to said die are interjoined.
13. A method according to claim 8 wherein said electromagnet further comprises a plurality of interchange able tips for changing the shape of the magnetic field.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US1915566 *||Aug 11, 1928||Jun 27, 1933||Kenneth Younghusband||Controlling electromagnets for lifting and transporting and in apparatus therefor|
|US3032363 *||Dec 24, 1959||May 1, 1962||Railway Automation Maintenance||Magnetic tie plate lifter|
|US3036245 *||Feb 24, 1960||May 22, 1962||Prep Ind Combustibles||Method of and apparatus for handling magnetizable material|
|US3341030 *||Mar 29, 1965||Sep 12, 1967||Eugene L Engels||Method and apparatus for positioning and orientating articles|
|US3435520 *||Feb 28, 1966||Apr 1, 1969||Texas Instruments Inc||Braze grounded lead header|
|US3543679 *||Apr 19, 1968||Dec 1, 1970||Western Electric Co||Silk screen apparatus for printed circuit boards|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US3868759 *||Nov 9, 1973||Mar 4, 1975||Gen Motors Corp||Magnetic pre-alignment of semiconductor device chips for bonding|
|US3868764 *||Nov 9, 1973||Mar 4, 1975||Gen Motors Corp||Multiple magnetic alignment of semiconductor devices for bonding|
|US3868765 *||Nov 9, 1973||Mar 4, 1975||Gen Motors Corp||Laminated template for semiconductor device bonding|
|US3887997 *||Nov 9, 1973||Jun 10, 1975||Gen Motors Corp||Magnetic alignment for semiconductor device bonding|
|US3887998 *||Apr 4, 1974||Jun 10, 1975||Gen Motors Corp||Air-biased probe for semiconductor device bonding|
|US3918146 *||Aug 30, 1974||Nov 11, 1975||Gen Motors Corp||Magnetic semiconductor device bonding apparatus with vacuum-biased probes|
|US3937386 *||Nov 9, 1973||Feb 10, 1976||General Motors Corporation||Flip chip cartridge loader|
|US3960279 *||Mar 28, 1975||Jun 1, 1976||General Motors Corporation||Magnetic alignment for semiconductor device bonding|
|US4995551 *||Apr 24, 1990||Feb 26, 1991||Microelectronics And Computer Technology Corporation||Bonding electrical leads to pads on electrical components|
|US5076485 *||Dec 20, 1990||Dec 31, 1991||Microelectronics And Computer Technology Corporation||Bonding electrical leads to pads with particles|
|US5128121 *||Apr 6, 1989||Jul 7, 1992||Nycomed As||Mixture of a positive and negative contrast agent for magnetic resonance imaging|
|US5321545 *||Nov 20, 1989||Jun 14, 1994||Biocom S.A.||Microscope stage for rapid and indexed analysis of filters and other media carrying multiple samples, and a method of analyzing such samples using said stage|
|WO1990004802A1 *||Oct 20, 1989||May 3, 1990||Biocom Sa||Stage for the rapid and indexed analysis with a microscope of filters and other supports carrying multiple samples, and method for analyzing such samples by using said stage|
|U.S. Classification||29/834, 228/180.21, 294/65.5, 228/212|
|International Classification||H01L21/687, H01L21/67|