JPH0222559B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for minimizing unpredictable error voltage sources in packaged precision analog components.

BACKGROUND OF THE INVENTION System designers who require precision analog components are always looking for more accurate components, i.e., to reduce error voltage or noise to the greatest extent possible without reducing reliability or increasing cost. I'm looking for the missing parts. Examples of this type of precision analog components include bipolar and FET input operational amplifiers, instrumentation amplifiers, voltage references, preamplifiers, isolation components, and multifunction circuits.

Noise sources or error voltage sources in this type of component are divided into two categories: predictable error voltage sources and so-called unpredictable sources. Predictable error voltage sources are compensated for by improved design, precision trimming, and improved manufacturing techniques, such as enclosing such components in hermetic packaging.

In the prior art, it has been found that there are two unpredictable sources of noise, one caused by temperature gradients in the die or IC chip of a component, and the other caused by temperature gradients in the packaged die or IC chip. Bonds in the leads of a component that is caused by the temperature difference between the bond within the package and the external bond to the conductor of the base printed circuit board (PC) to which the package surrounding the component is attached. It is. One conventional method for minimizing error voltages from such sources is to install the entire system in which the sensitive components are part within a suitable enclosure that maintains all components at a substantially constant temperature. It is to surround. A conventional solution to the thermal gradient problem is to provide the components with on-chip stabilization circuitry that maintains the temperature of the chip or die substantially constant. However, in many applications, these conventional approaches to the problem of minimizing error voltages in precision analog components are not possible or economically difficult. A problem unsolved by conventional techniques is to reduce so-called unpredictable sources of error in individually packaged precision parts to the entire system of which they are a part in one ideal environment. or how to minimize the entire system without having to package it in one ideal environment; in other words, how to minimize the need for each packaged precision analog component to have its own idealized It's about how we provide the environment.

SUMMARY OF THE INVENTION As previously mentioned, precision analog electronic components such as operational amplifiers have been found to have two unpredictable sources of error voltage or noise. One source is caused by temperature gradients in the die or chip of the part. This noise source is minimized by maintaining the temperature substantially constant throughout the die or chip of the component. The other source is the thermoelectric voltage generated by the so-called thermocouple effect, when the dissimilar metal contacts at the internal and external junctions of the package leads are at different temperatures when the package is attached to a substrate. be. This source of error voltage or noise can be minimized by maintaining the junction of each lead of the package substantially constant.

The inventors have also discovered that there is a third, unpredictable source of error voltage. The leads in packages of the type commonly used to enclose components of this type are insulated from each other and from the container by glass insulators. The inventors have discovered that light that is primarily reflected from the surface of the substrate to which the package is attached is transmitted through the glass insulator of its base and into the interior of the package, thereby causing light-responsive circuitry in the component. It was found that the photovoltaic voltage generated during this process becomes another source of noise or error voltage.

To minimize unexpected error voltage or noise sources in individually packaged precision analog components, a heat sink with a significant thermal mass is placed around the package after the components are mounted on the substrate. , so that the heat sink makes good thermal contact with the outer surface of the precision analog component package. Heat sinks are made of materials with high specific heat and good thermal conductivity. The outer surface of the heat sink is provided with fins or protrusions or has a highly emissive surface finish to allow heat to be transferred from the heat sink to the surrounding environment by radiation and conduction. This heat sink maintains the temperature of the package with which it is in contact substantially constant after an initial warm-up period.

The heat sink is provided with a depending integral skirt to provide an isothermal enclosure for the space between the base of the package containing the component and the surface of the substrate to which the packaged component is attached. This skirt substantially contacts the surface of the substrate to form an isothermal chamber when the heat sink is properly positioned in the package. This skirt has
Also, highly radiative surfaces are provided to block or absorb incident radiant energy. Otherwise, the incident radiant energy would pass through the glass seal around the leads at the base of the package and into the interior of the package, creating an error voltage due to the photoelectric effect. The isothermal envelope formed by the heat sink skirt maintains the internal and external junctions of the package leads at a substantially constant temperature, thus reducing the thermoelectric error voltages generated by these junctions. Minimum.

It is an object of the present invention to provide a method and apparatus for minimizing error voltages from unpredictable sources and packaging noise in packaged precision components.

Another object of the present invention is to provide a method and apparatus for providing individually packaged precision components with an ideal environment that minimizes environmentally generated error voltages or package noise in each component. That's true.

Yet another object of the present invention is to provide a method and apparatus for minimizing light-induced errors in packaged precision electronic analog components in hermetic packages.

It is a further object of the present invention to provide individually packaged precision analog components mounted on a substrate with a skirted heat sink that maintains a substantially constant temperature within the package between the base of the package and the substrate. The purpose is to provide a substantially isothermal enclosure so that incident radiant energy is substantially transmitted internally through the glass insulating seal around the leads of the package without producing opto-electrical noise.

Embodiments Next, the present invention will be described in more detail with reference to embodiments of the present invention based on the accompanying drawings.

In FIG. 1, a precision analog operational amplifier 10 disposed in a hermetic package 12 is schematically illustrated. In this preferred embodiment, package 12 is designated as TO-99. Package 12 includes a cylindrical metal can 14 having an integral top surface 16. A metal eyelet 18 is attached to the lower open end of the can 14. Leads 20-1 through 20-8 extend through openings in eyelet 18 and are held in place by glass seals 22, insulating them from each other and from package 12. The eyelet 18 and seal constitute the base 24 of the package 12. An insulating spacer 28 protrudes from the bottom surface 26 of the base 24. The package part 10 is
It is attached to a substrate, that is, a PC board 30.
One end of leads 20-1 and 20-8 are coupled to a conductive path on substrate 30, and the other end is coupled to a conductor within the package.

In this preferred embodiment, leads 20-1 and 20-8 are formed of Kovar with a layer of gold. The gold layer forms an internal bond for the leads 20 inside the package and an external bond for the leads 20 outside the package 12. In FIG. 1, lead 2 is connected to inverting input 32 of operational amplifier 10.
0-1 and lead 2 connected to non-inverting input 32
The width of leads 0-3 is shown as being larger than the other leads 20 as an example. The internal and external junctions of leads 20-1 through 20-8 generate thermoelectric voltages between the Kovar leads and the gold, copper, or solder layers at their ends. Under certain circumstances, these junctions generate relatively significant error voltages. Most of the important sources of thermoelectric voltages that affect the operation of operational amplifier 10 are
Symbolically shown in the figure. Therefore, thermoelectric voltage source 3
6 (VTA°) is the thermoelectric voltage generated by the internal bond between lead 20-1 and the metal to which it is bonded. Source 38 (VTB°) is a voltage source generated by the external junction of lead 20-1, and source 40 (VTC°) is a voltage source generated by the external junction of lead 20-1.
Source 42 (VTD°) represents the thermoelectric voltage source generated by the internal junction of lead 20-3.

Other error voltage sources that constitute or are defined as package noise are source V (T1° - T2°) and source 46V.
(LIGHT). Source 44 symbolically represents the source of error voltage resulting from the temperature gradient (T1°-T2°) present across the die or IC chip of operational amplifier 10. A source 46 generates incident radiant energy 4 from an external or ambient light source that is reflected from the top surface 50 of the substrate 30 through the seal 22.
8 represents the resulting error voltage source. When that light is absorbed by the light-responsive circuitry of operational amplifier 10, it generates a light voltage V(LIGHT). Since the thermal gradient error voltage generated by source 44 is a function of the temperature difference across the die ends of operational amplifier 10, this voltage can be reduced by reducing the temperature gradient across the die ends of operational amplifier 10. can be minimized. The magnitude of the photoelectric error voltage generated by photovoltaic power source 46 is determined by the magnitude of the photoelectric error voltage generated by photovoltaic power source 46 when light
This can be minimized by preventing it from entering the interior of 2. By maintaining the internal and external junctions of leads 20 at substantially the same temperature, the outputs of sources 36, 38, 40, and 42 are the same, and the internal and external junctions of leads 20-1 and 20-3 are maintained at substantially the same temperature. The thermoelectric voltages generated by these sources cancel out and the error voltage from these sources becomes essentially zero.

2 and 3, skirt heat sink 52 includes a cylindrical ring 54. In FIGS. The inner diameter of the ring is slightly smaller than the diameter of the outer cylindrical surface 58 of the package 12.
The outer surface 60 of the ring 54 is provided with a plurality of substantially equiangularly spaced radial ridges or fins 62. Suspending from ring 54 is an integral cylindrical skirt. The inside diameter of the skirt 64 is slightly larger than the diameter of the rim 66 of the eyelet 18. Ring 54 is used to facilitate placement of heat sink 52 in package 12.
A slit 68 may also be formed in the skirt 64.

The heat sink 52 is preferably made of a material with relatively high specific heat and good thermal conductivity. heat sink 5
2 has an outer surface finish 70 for maximum radioactivity.
is applied. In a preferred embodiment, member 54
is made from aluminum and has a finish of 70.
It is hard black anodized.

Package 12 containing precision analog components 10 sensitive to error voltages at the microvolt level
is attached to substrate 30 in a conventional manner. That is, the bottom surface 26 of the base 24 of the appacage 12
are substantially uniformly spaced from the top surface 50 of the substrate 30 by a distance substantially equal to the height of the spacer 28 . This allows standard board application techniques to be used to attach the package 12 to the board 30 and also allows the heat sink 52 to be attached to the outside surface 58 of the can 14 of the package 12.
Debris caused by the manufacturing process can be removed before positioning on or around. heat sink 5
Due to the elasticity of 2 and the slit 68, the ring 52
The heat sink 52 can be relatively easily positioned in the package 12 so as to provide good thermal contact between the inner surface 56 of the can 14 and the outer surface 58 of the can 14. Ring 52 is positioned on package 12 such that the lower inner portion of ring 54 contacts rim 66 of eyelet 18. In this case, the skirt 64 substantially encloses the space between the base 24 of the package 12 and the upper surface 50 of the substrate 30 below.

The properties of heat sink 52, namely its mass, specific heat, and thermal conductivity, provide a large thermal mass compared to the heat source within the package. The relatively large exposed surface area of heat sink 52, combined with the radiative nature of its surface finish, allows heat sink 52 to transfer heat from heat sink 52 to the surroundings of package 12 by radiation and conduction. These characteristics of heat sink 52 minimize temperature gradients at the die end of device 10 when operating conditions stabilize. This occurs relatively soon after power is applied to device 10. The hanging skirt 64 together with the base 24 of the package 12 and the top surface 50 of the printed circuit board 30 below the package 12 creates a substantially closed chamber in which the leads 20 are disposed. The temperature in this chamber quickly becomes isothermal after the device 10 is energized, thus creating an isothermal greenhouse. Skirt 64 also greatly reduces airflow into space 72 from outside the skirt. This air flow is another potential source of thermoelectric noise. A skirt 64 extending substantially to the top surface 50 of the substrate 30 effectively shields the base 24 of the package 12 from the environment, such that each shield 52
2 to create an environment that minimizes error voltages or package noise in precision analog components packaged in hermetic enclosures such as those illustrated and described herein.

In a preferred embodiment, the heat sink 52
The inner diameter of the ring 54 is 0.318 inches, the diameter of the outer surface of the ring 54 is 0.440 inches, and the total diameter of the heat sink 12 is 0.625 inches. The inside diameter of skirt 64 is 0.380 inches and the outside diameter is 0.430 inches. The total height of the skirted heat sink 52 is 0.325 inches.

After the package 12 is attached to the board 30, the heat sink 52 with a skirt is attached to the package 1.
2 is provided with a slit 68 to facilitate positioning of the heat sink. The heat sink 52 does not need to be provided with the slit 68.
In this case, the heat sink 52 must be precisely made, particularly the diameter of its inside surface, to provide a sliding or spring fit between the inside surface of the heat sink and the outside surface of the package.

It will be clear that, apart from the embodiments described above, various modifications may be made without departing from the scope and spirit of the invention.

[Brief explanation of drawings]

Figure 1 is a block diagram of a packaged precision analog component to identify sources of unexpected error voltages;
FIG. 2 is a plan view of the skirted heat sink of the present invention, FIG. 3 is a sectional view taken along the line 3-3 in FIG. 2, and FIG. FIG. 3 is a side view of the heat sink shown in FIG. 10... Precision analog operational amplifier, 12... Airtight package, 14... Cylindrical metal can, 18...
...Metal eyelet, 20-1 to 20-8...Lead, 22...Glass seal, 24...Base, 2
8... Insulating spacer, 30... Substrate, 52... Heat sink with skirt, 54... Cylindrical ring, 62... Fin, 64... Cylindrical skirt,
68...slit.

Claims (1)

Claims: 1. An apparatus for creating a heat sink and reducing undesired electronic disturbances in an electronic element attached to a substrate, comprising: heat sink means having good thermal conductivity in contact with and surrounding the element, the heat sink means having a protruding portion surrounding the space between the bottom portion of the electronic element and the substrate; A device characterized in that it constitutes a conductive and radiative barrier which shields the bottom part of the electronic component from noise sources.