FR2562750A1 - METHOD AND APPARATUS FOR MINIMALLY REDUCING PARASITE NOISE IN PRECISION ELECTRONIC COMPONENTS - Google Patents

Abstract

METHOD AND APPARATUS FOR MINIMIZING UNPREDICTABLE SOURCES OF PARASITE NOISE OR ERROR VOLTAGES OF THE MICROVOLT ORDER IN PRECISION ANALOGUE COMPONENTS. AROUND THE CYLINDRICAL CASE 12 CONTAINING THE COMPONENT SEPARATE FROM THE PLATE 30 CARRYING A CIRCUIT PRINTED BY A SPACER 28, A COOLING ELEMENT 54 OF SENSITIVELY CYLINDRICAL SHAPE, PROVIDED WITH EXTERNAL FINS, AN INTERNAL BORE AND A LOWER COLLAR 64, INTENDED TO SURROUND THIS INTERVAL, WHILE BEING IN EFFECTIVE THERMAL CONTACT WITH THE COMPONENT HOUSING, THE WALL OF THIS COOLING ELEMENT BEING RELATIVELY THICK, SO AS TO FORM A SENIALLY ISOTHURSE-DRIVEN ENCLOSURE OWN THE EACH INCIDENTAL LIGHT AS WELL AS TEMPERATURE DIFFERENCES BETWEEN THE CONNECTIONS OF THE COMPONENT CONDUCTORS AND OTHER METALS. APPLICATION TO ELECTRONIC COMPONENTS, ESPECIALLY OPERATIONAL AMPLIFIERS.

Description

256275J

  Methods and apparatus for minimizing unpredictable sources of error voltage faults in

  Precision analog component blocks.

  System designers requiring precision analog components are constantly seeking more precision in such systems.

  components, ie components in which the voltages of

  noise or noise is reduced to a minimum, in the largest

  possible, without compromising reliability or increasing the

  be the cost of these components. Typical examples of such composi-

  analogical precision machines, we can mention the amplifiers

  bipolar and field-effect transistors, instrument amplifiers, reference voltages, preamplifiers,

  discrete components and multi-function circuits.

  The sources of noise, or error voltages, that such components may present may fall into two categories, namely the

  predictable sources of error voltages and sources known as unforeseen

  ble. Predictable sources of error voltages can be compensated for by improved design, tuning, or balancing, and advanced manufacturing techniques, including

  the technique of enclosing these components in hermetically sealed

  c. The prior art has demonstrated two unpredictable sources of noise that were due to temperature gradients in integrated circuit blocks or chips, the component, and also through temperature differences between component lead connections. included in the block or chip, one of the connections being internal or embedded in the block, while the other is external and made with drivers

  carried by the substrates, supports or circuit boards on the

  which block containing the component is mounted. One of the solutions

  prior art with a view to minimizing the definite sources of

  above is to enclose the entire system, of which

  part or components of precision, within a

  appropriate to maintain the totality of the elements at a temperature

  substantially constant. A solution provided by the prior art to solve the problem of the thermal gradient is to provide on the chip

  the components of a stabilizing circuit, this circuit maintaining the

  the chip, or block, to a substantially constant value.

  However, in many applications the solutions proposed by

  prior art to solve the problem of minimizing

  Errors in precision analog components are either inapplicable in practice or unacceptable for economic reasons. The problem not solved by the prior art is the following: how to minimize the so-called unpredictable sources of error voltage in precision analog components contained in blocks or chips without the need to provide the entire system which includes the component of an ideal environment, or to enclose it; or, in other words, how to provide each component

  precision analogue so included in a system its own environ-

idealized.

  As noted above with respect to the prior art, the latter has identified two sources of unpredictable error voltages, or unwanted noise, in precision analog components, such as, for example, operational amplifiers, of these sources being

  due to temperature gradients in the blocks or chips of the component.

  This source of unwanted noise can be minimized by maintaining

  at a substantially constant value the temperature in all blocks or chips containing components. Another source is

  in the thermoelectric voltages produced by the contact between

  rates dissimilar to drivers' internal and external connections

  of the system when it is mounted on a substrate, in case

  nexions would be subject to different temperatures, which is

  shovels the thermo-torque effect. If we manage to maintain connections

  each of the conductors of the system at temperatures substantially equal to

  the, we will minimize this source of error voltages or noise. The Applicant has also discovered a third source of unpredictable error voltages. Drivers of the type of system or block commonly used to enclose components

  are isolated from each other and from the envelope of the system by the usa-

  glass age. The Applicant has discovered that the light reflected at the origin

  The surface of the substrate on which the block is mounted can be transmitted to the interior of this block through this glass insulator of the base, this light producing photoelectric voltages in the photosensitive circuits of the component, which constitutes another source

noise or error voltages.

  To minimize unpredictable causes of tension

  error or noise in analog components

  contained in blocks, according to the invention an element 3 -

  or cooling plate having a relatively high thermal mass

  bearing around the periphery of the block in question, by establishing an effective thermal contact with the external surface of the block containing the

  analog component, after mounting the component on a subsystem

  trat. The cooling element is made of high specific heat material and having excellent thermal conductivity. Her

  outer surface is provided with fins or similar projections, and

  also has a superficial finish characterized by the fact that

  is very emissive so that the heat coming from the heating element

  cooling is transferred by radiation and convection to the environment.

  ambient. The cooling element essentially maintains the internal temperature of the block with which it is in contact at a level

  which is substantially constant after an initial heating period.

  To obtain an isothermal enclosure to enclose the

  valle which separates the base of the block containing the component from the surface of the substrate on which the component included in this block is mounted,

  the cooling element of a hanging skirt which forms an integral part

  which, when the cooling element is correctly placed on the block, is kept practically in contact with the surface of the

  substrate so as to constitute an isothermal chamber. This skirt, which

  Moreover, it has a highly emissive surface that blocks or absorbs

  incident radiant energy which otherwise could be transmitted through

  to the hermetic glass seals that surround the conductors in the base of the block to gain the inside of this block and produce

  error voltages by photoelectric effect. The isothermal enclosure

  worn by the skirt of the cooling element keeps the connections

  internal and external conductors of the block at a sensible temperature-

  which minimizes thermoelectrically induced error voltages and could possibly be determined by

these connections.

  Therefore, it is an object of the present invention, inter alia, to provide a method and apparatus for minimizing

  error voltages due to unpredictable sources, or

  sites, in precision electronic components assembled in

chips or blocks.

  Another object of the invention is to provide a method and apparatus for performing for each embedded precision component

  individually in a block or chip an ideal environment in order to

  minimum, in such components, the error voltages or all

2S62750

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  block noise or chip due to the environment.

  However, it is also an object of the invention to provide a method and apparatus for minimizing error voltages due to

  light in precision electronic analog components

  closed in fleas or sealed blocks. Furthermore, the invention also aims to provide, for

  precision analog components embedded in blocks or chips

  and arranged on a substrate, a cooling element provided with a skirt adapted to maintain the internal temperature of the block or chip to a substantially constant value and to form a substantially isothermal enclosure between the base of the block or chip and the substrate, while virtually preventing transmission of radiant energy through the glass insulator surrounding the chip or block leads to the interior,

  in order to avoid causing noise interference by photoelectric effect.

  Other purposes, features and advantages of this

  will become clear from the description which follows

  a preferred embodiment of the invention, given by way of non-limiting example. On the drawing:

  FIGURE 1 is a block diagram showing an analog component

  FIG. 2 is a plan view of the cooling element provided with a skirt, in accordance with the present invention; FIGURE 3 is a section taken along line 3-3 of Figure 2; and

  FIGURE 4 is a side elevational view of the reflector

  Figure 3, after its application around the assembled block

on a substrate.

  Referring first to Figure 1 of the drawing, there is shown, diagrammatically, an analog operational amplifier of

  10 in a block or chip 12. In the preferred mode of

  This block or chip 12 is made in the form of a T0-99. This block 12 comprises a cylindrical metal housing 14 whose upper face 16 is an integral part. A disc or metal capsule 18 is fixed in the open bottom end of the casing 14. The conductors 20-1 to 20-8 pass through openings provided for this purpose in the disc 18 where they are held in place and isolated from each other and by compared to the block 12 by a casting 22 of sealing glass. The disc or capsule 18 and the glass 22 constitute the base 24 of the block 12. An insulating spacer 28 - 5 projects under the lower face 26 of the base 24. The component 10 thus encapsulated can be mounted on a substrate or support, for example for example, a printed circuit board 30, the conductors 20-1 to 20-8 being welded at one end to conductive lines provided on the substrate 30 and at the other end to internal conductors of the block 12. In the preferred embodiment of FIG. realization, the conductors 20-1 to 20-8 are made of Kovar alloy, a gold layer forming the connections

  between the conductors 20 inside the block 12 and the con-

  external connections of these same conductors 20 which are outside the block 12. In FIG. 1, the respective widths of the conductors -1 connected to the inverting input 32 of the operational amplifier and the connected 20-3 conductor on the non-inversion input 34 are represented as being larger than those of the other drivers

  , but only to clarify the graphical representation. The con-

  internal and external connections of the conductors 20-1 to 20-8 produce thermoelectric voltages at these connections between the Kovar conductors and the layers of gold, copper or other metal or alloy welding at the ends of these conductors, these connections, in in some cases, being likely to generate error voltages of a relatively large amplitude. The most significant generators or sources of thermoelectric voltages that may affect the operation of the amplifier

  10 are symbolically designated in FIG.

  Thus, the thermoelectric voltage source 36 (VTo) is constituted by the thermoelectric voltages produced by the internal connection between the conductor 20-1 and the metal to which it is welded. The generator 38 (VT0) designates the voltage source produced by the external connection of the B

  driver 20-1; the generator 40 (VTc) designates the voltage source pro

  by the external connection of the conductor 20-3, and the generator 42

  (VTO) means the source of thermoelectric voltage produced by the

D

internal connection of the driver 20-3.

  Other sources of error voltages, or noises that con-

  or are defined as noise from blocks or puffs

  these are the 44 V (T <- T2) generators and the 46 V (Light) generator.

1 2

  Generator 44 symbolically represents a source of error voltages due to temperature gradients (TO-TO) that exist across the

  integrated circuit chip or chip of the operational amplifier 10. The

  nter 46 represents the sources of error voltages produced in

  sound of incident radiant energy 48 due to the presence of light sources

  external or ambient bending machines whose rays are reflected by the upper surface 50 of the substrate 30 through the sealing glass 22, this light, when absorbed by the photosensitive circuits

  of the operational amplifier 10, producing photoelectric voltages

  V (Light). Whereas the thermal gradient error voltage which is due to the presence of this generator 44 is a function notably of the

  temperature differences that exist in the block or chip of the amplifier

  In the operational indicator 10, this voltage can be lowered or reduced to its minimum level by decreasing the temperature gradient across the block or chip. The magnitude of the photoelectric error voltages produced by the photoelectric source 46 can be minimized by preventing light from entering the interior of the block 12.

  maintain the internal and external connections of the drivers 20 sensi-

  at the same temperature will give the outputs of the generators 36, 38 and 42 virtually the same value, so that the voltages

  thermoelectric effects produced at the internal and external connections of

  coils 20-1 and 20-3 will cancel and therefore the error voltage

  from these sources will be reduced to almost zero.

  In FIGS. 2 and 3, it can be seen that the skirted cooling element, designated at 52, comprises a kind of cylindrical hub 54 whose diameter of the internal surface 56 is slightly smaller than the

  diameter of the outer cylindrical surface 58 of the block 12. The outer surface

  dull 60 of this cylindrical hub 54 has several protrusions or ailer-

  your radials regularly spaced 62. Under the hub 54 protrudes a

  cylindrical collar 64 which forms an integral part. The diameter

  The flange 64 of this flange 64 is designed to be smaller than the diameter of the annular flange 66 of the disc or capsule 18. In order to facilitate the installation of this cooling element 52 on the block 12, provision can be made for

  slot 68 in hub 54 and flange 64.

  The cooling element 52 will preferably be made of

  which has a relatively high specific heat and a good

  thermal ductility. The cooling element 52 has a

  face or exterior finish 70 having a maximum emissivity. In the

  preferred embodiment, the flange 54 is made of aluminum and the finish

  70 is a hard anodic black layer.

  The block or chip 12 containing the precision analog component sensitive to microvolt error voltages is mounted on the substrate 30 according to the conventional mode, the lower face 26 of the base 24 of the block 12 being substantially separated from the the upper surface 50 of the substrate 30 by a uniform interval substantially equal to the height of - 7-

  28. This allows not only the adoption of

  standard technical dice for mounting the block 12 on the printed circuit board 30 but also to remove any fragments or debris dice in the manufacturing process before placing the cooling element 52 on or around the outer surface 58 of the casing 14 of the block 12. The elasticity of this cooling element 52 and the existence of the slot 68 facilitate the correct placement of this cooling element 52 on the block 12 while establishing an excellent thermal contact between the inner surface 56 of the element 52 and the outer surface 58 of the casing 14. The cooling element 52 is placed on the block 12 so that

  that the lower inner part of the cylindrical hub 54 can be

  held in contact with the annular flange 66 of the disc or capsule 18. Under these conditions, the skirt 64 will substantially enclose the gap formed between the base 24 of the block 12 and the upper face 50 of the substrate 30 placed under

the block that it supports.

  The characteristics of the cooling element 52, its mass, its specific heat as well as its thermal conductivity give it a considerable thermal mass in comparison with those of the heat sources which are inside the block. The exposed and relatively extended surfaces of this cooling element 52, as well as the emissivity of its surface finish 70 allow this element 52 to transfer heat by radiation and convection between the element 52

  and the ambient environment of this block 12. These characteristics of the

  52 minimize the temperature gradients

  in the block formed by the device 10 as soon as the conditions of

  have stabilized, which is occurring relatively quickly.

  This pendant flange 64 and the base 24 of the block 12 and the upper surface 50 of the printed circuit board 30 located under the block 12 define between them

  practically closed chamber in which the conductors are located 20.

  In this room, the temperature then becomes rapidly isothermal,

  which forms an insulated chamber shortly after the placing on

  The flange 64 also contributes to braking the air currents from outside the flange which could enter the gap 72, these currents being of course other potential sources of noise. -N5ectriques parasitic induced, the flange 64 which extends pri-: iquiice: juqSquea surface superior 50

  of the substrate 30 effectively protects the base 24 of block 12 against energy.

  radiant gas incident in the atmosphere of the ambient environment, each

  The element 52 thus creating an environment around the block 12 so as to minimize error voltages or block noise,

  in precision analog components housed in

  such as that shown and described here.

  In the preferred embodiment of the invention, the inner diameter of the cooling element 52 is 8.08 mm, the diameter

  the outer surface of the hub 54 is 11.17 mm, and the outside diameter

  all of the cooling element 12 is 15.87 mm. The diameter

  Flange dull 64 is 9.65 mm and its outer diameter is 10.92 mm.

  The total height of the flanged cooling element 52 is

of 8.25 mm.

  The cooling element 52 with collar 64 has a slot 68 intended to facilitate its installation on the block 12 after the latter has been removed.

  mounted on the substrate 30. The cooling element 52 may be

  Without this slit 68, it would be necessary if the degree of manufacturing accuracy of this element 52, particularly with regard to the diameter of its internal surface, were such that it allows a sliding fit between this inner surface of the slab. element 52 and the outer surface

  of the block, which is equivalent to an elastic adjustment.

  It is obvious to any specialist in the art that variations and modifications may be contemplated apart from those suggested herein.

  without however departing from the basic principles of the invention.

2562750 '

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Claims (20)

R E V E N D I C A T I 0 N S CLAIMS   An apparatus for producing a cooling effect and reducing unwanted electronic noise in an electronic component (12) mounted on a substrate (30), the apparatus comprising a cooling element (52) having good thermal conductivity and being in thermal contact with said electronic component (12) so as to   maintain this electronic component at a practical temperature   constant, this apparatus being characterized by comprising means (64) for surrounding the gap   formed between a lower part (24) of said electrical component   tronic (12) and who is in contact with this element of   cooling (52) and with said substrate (30), for the purpose of   protect this lower part (24) of the electronic component   against electromagnetic radiation and thus prevent the generation of electronic noise said electronic component.   2. Apparatus according to Claim 1, characterized by   said means (64) for surrounding the pre-existing gap   cited has the effect of minimizing unpredictable noise in electronic devices (10) mounted in an airtight block (12), the block having a flat base (24) provided with conductors (20-1 to 20-8) which emerge from this base (24), this block (12) being mountable on a   planar surface (50) of said substrate (30).   Apparatus according to Claim 2, characterized by   the cooling element (52) is provided with a plurality of fins (62).   Apparatus according to Claim 3, characterized in that the cooling element (52) is provided with a   highly emissive surface finish (70).   5. Apparatus according to claim 4, characterized in that the cooling element (52) is made of aluminum. Apparatus according to Claim 5, characterized in that the highly emissive surface (70) is constituted by a black and hard anodic layer.   Apparatus according to any one of Claims 1 to 6,   characterized in that said base (24) comprises a seal - 10 -   a glass (22) surrounding the conductors (20-1 to 20-8) and a spacer (28) projecting from a certain   distance under said base (24), said cooling element   ment (52) comprising a hub (54) of high-friction material   their specificity and thermal conductivity, an inner surface (56) and an outer surface (60), the inner surface (56) being adapted to come into effective thermal contact with the sides of the block (12), while the outer surface (60) of the cooling element (52) is highly emissive, the   means for enclosing said gap comprising a collar   lerette (64) provided with an edge made of said material and   protruding under said hub (54) over a distance   pre to form a substantially isothermal enclosure between the base (24) of the block (12) on which is placed said cooling element (52) and the surface (50) of the substrate (30) on which the block (12) is fixed, and also to prevent incidental radiation from striking the sealing   glass (22) of the base (24) of the block (12).   Apparatus according to Claim 7, characterized in that said cooling element (52) and said means   surround (64) are made of aluminum.   Apparatus according to Claim 8, characterized by   the collar (64) is an integral part of the cooling element (52).   10. Apparatus according to Claim 9, characterized in that the cooling element (52) and its flange (64) are slotted in order to facilitate the installation of the cooling element (52) and its collar (64) on the block (12).   11. Apparatus according to Claim 1, characterized in that it comprises: a) a circuit board on a board (30) having a substantially planar upper surface (50); b) an electronic component (10) housed in a sealed block or chip (12), said block having a plane base (26) from which a plurality of conductors (20-1 to 20-8) emerge connected to the electronic component (10) and a cylindrical outer wall, the base (26) of this block surmounting the surface (50) of the board (30) of the printed circuit while being separated from - 1l -   this surface by a determined distance;   c) a cooling element (52) provided with an   cylindrical inner face (56) and an outer surface (60),   this element fitting on the block (12) so that the   inner core (56) of the cooling element (52) is in effective thermal contact with the outer wall of the   block (12), said outer wall (60) of the cooling element   (52 "being provided with a plurality of fins (62) as well as a highly emissive surface finish (70), and d) a cylindrical flange (64) which protruded   under said reset element (52) until a dis-   same distance to the end distance according to b) 0 in order to   close sensibl.ement 1 interva! the subsistence between the base   (26) of the b! C'c (12 ') and the   1 cooked: imo'rim 309) 1. pj; .i 1 e3lon the pRevenica: -in i! characterized by the fact that the cooling element (52) is manufactured in alunniniJur.   3. S is.l ... se.1on ..... 2, charactrised by the 0 wfait that the 2inition emisszve (70) of the element de frove dissemen-. (52) is composed of a hard black anodic layer, 14, Apparatus for Revenge, 3, characterized by   : the block, .12). i ... no spacer (2-) '-   2!.: OS sa. base e. and that is not 7 AULI: it was sensibly equal said distance said it-e: 5. Apparel-lcna 3t2vedi ati ln caracterized it does it so elem.ent .de e-.t ... (52) the glue: te, are split in order to fi 3 '' er ', - raise up on ie block ({L -.   6. '... the t ... aaca'eres by the mean: laele diae the internal ff ae (56) of the Aent re rúf cidis0seen't (52) e-st legee : a = nt inferior to the dia'tere of su ', r :: w: = e-erne of the block (l2) 17. e pcur! 1 '' - '' '' '' '' '' '' '' '' '' '' '' '' '' '' '' 'of 3 "   conque of the R - ?. i.o- J.:2 l: -.- e-ie -'-e iz. cu el! e c ('- nsi.s: _   in order to achieve a clear (52)   born to reduce noise ... 'ronin2es parasites and indesila = - 12 -   in an electronic component (12) mounted on a sub- strat (30);   (b) provide a cooling element (52) with   with good thermal conductivity and maintained in   tact with said electronic component (12), and   (c) to enclose the space formed between a lower part   re (24) of said electronic component (12) and said substrate (30) to protect this lower part of the electronic component against electromagnetic radiation in this component.   18. A method according to claim 17, characterized in that it comprises the steps of: a) placing said high thermal mass cooling element (52) in effective thermal contact with the block (12); b) to dissipate by radiation and convection the heat   accumulated in this cooling element (52), and -   c) enclosing the gap formed between the block (12) and   the substrate (30) so as to provide a sensitive chamber isothermal.   19. Method according to claim 18, characterized in that said cooling element (.52) is manufactured in aluminium.   20. Method according to any one of the claims 18   and 19, characterized in that the cooling element   (52) is provided with outer fins (62).   21. Method according to claim 20, characterized in that said cooling element (52) is provided   a surface finish (70) with high emissivity.   22. Method according to claim 21, characterized in that said cooling element (52) is provided with a slot (68) intended to facilitate its effective thermal contact with the block (12) containing the electronic component. 23. Method according to Claim 18, characterized in that the base (24) of the block (12) is protected against   incidental electronic radiation.   24. The method of claim 23, characterized by   block (12) has a cylindrical outer surface - 13 -   and that the cooling element (52) has a   cylindrical inner surface (56).   25. The method of claim 24, characterized by   the outer surface of the cooling element   ment (52) is provided with a plurality of fins (62). 26. A method according to claim 25, characterized by   the outer surface (66) of the cooling element   deformation (52) has a highly emissive finish (70).   27. Method according to Claim 26, characterized in that the cooling element (52) is made of aluminum.