WO2001090710A1

WO2001090710A1 - Thermocouple passing through encapsulant of integrated circuit

Info

Publication number: WO2001090710A1
Application number: PCT/SG2000/000076
Authority: WO
Inventors: Kamel Fauzi Razali
Original assignee: Kamel Fauzi Razali
Priority date: 2000-05-25
Filing date: 2000-05-25
Publication date: 2001-11-29
Also published as: TW523883B; AU2000246385A1

Abstract

An IC device (10) has a semiconductor die (12) embedded within an encapsulating material (14), and a thermocouple (22) having a junction (24) directly attached to a surface of the die (12), (to allow accurate measurement), wherein the thermocouple (22) passes through the encapsulating material (14) for cennection to a temperature measuring circuit (not shown). A method of making the device (10) involves (a) etching away the encapsulation (14) of the device (10) to expose a surface of the die (12), (b) attaching a junction (24) of a thermocouple (22) directly onto the surface of die (12), and, (c) refilling the cavity (18) formed by the etching step with a casting compound. The device (10) is used for calibrating the chamber temperature of a test handler in which IC devices are soaked to reach a predetermined temperature prior to electrical testing.

Description

THERMOCOUPLE PASSING THROUGH ENCAPSULANT OF INTEGRATED CIRCUIT

Technical Field

This invention relates to a temperature sensing integrated circuit (IC) device and to method of making such a device.

Background

During the manufacture of IC devices, it is normal for the devices to be electrically tested whilst they are held at certain temperatures. These temperatures reflect the expected operating environments for the devices being tested. Typical set testing temperatures are 25°C and 100°C, however other testing temperatures may be specified, for example for ICs to be used in military or space applications, final testing temperatures of -55°C and 150°C may be specified.

Various testing devices have been developed to perform final electrical tests on IC devices at high rates of speed and machines called test handlers have been developed which feed singulated IC devices to and away from test sites interfacing with a tester at the desired rates of speed. These test handlers include chambers within which the IC devices to be tested are soaked to the specified test temperature. To ensure that the chamber temperature of a test handler is accurate relative to the set test temperature, the chamber is routinely calibrated using a number of temperature sensing devices which are strategically positioned within the chamber. An example of such a calibration regime is disclosed in United States Patent No. 5287294.

Known temperature sensing devices used for such calibration have comprised an IC device having a hole drilled therein into which a wire thermocouple is inserted. This set up, however, is only possible with medium or large sized IC devices such as for example DIP (Dual-in-Line Package), PLCC (Plastic Leadless Chip Carrier), QFP (Quad Flat Package), PQFP (Plastic Quad Flat Package) etc. packages. For small packages, such as for example SOIC (Small Outline Integrated Circuit), TSOP (Thin and Small Outline Package), TSSOP (Thin, Shrinked and Small Outline Package), Micro BGA (Ball Grid Array) etc. types of devices, the devices are so small that a thermocouple junction cannot be inserted into them and thus the bare thermocouple junction is used to sense the chamber temperature. ^•

It is important for the integrity of the testing regime and thus ultimately the reliability of the IC devices that the temperature at which an IC device is tested be accurate relative to the set testing temperature. However the above described known temperature sensing devices used for calibrating the test temperature allow inaccuracies to occur in a calibration. That is, for small IC devices there is no sensing at all of the temperature within the package at the die, and for the larger IC devices in which a thermocouple junction is inserted into a pre-drilled hole, the exact location of the junction relative to the actual die location is often uncertain because the drilled hole may fall short of the die. Another problem is that the drill may overshoot the actual die location thereby damaging it.

Summary of the Invention

The present invention seeks to provide a temperature sensing integrated circuit device for use in calibrating a test handler, and a method of making such a device, in which the chance for inaccuracies to occur in use in sensing the temperature of the die within the device are minimised.

Accordingly, in a first aspect the present invention provides a temperature sensing integrated circuit device comprising, a semi-conductor die embedded within encapsulating material, and a thermocouple having a junction which is directly attached to a surface of the die, wherein the thermocouple passes through the encapsulating material for connection to a temperature measuring circuit.

In a second aspect the invention provides a method of making a temperature sensing integrated circuit device comprising, providing an integrated circuit device having a semi-conductor die embedded within encapsulating material, exposing at least a portion of a surface of the die by removing some of the encapsulating material, attaching a junction of a thermocouple directly onto said exposed die surface, and ₍ applying casting compound to replace said removed encapsulating material to re-encapsulate the die and the thermocouple passing through the encapsulation.

Preferably in the second aspect of the invention and for a plastic encapsulating material, at least a portion of the surface of the die is exposed by etching away the encapsulating material. For an IC having a ceramic encapsulating material, the die surface may be exposed mechanically, using a special instrument and tool. Preferably the thermocouple comprises dissimilar metal wires which are welded together to form a junction and this junction is directly attached to the exposed top die surface. The wires for the thermocouple are chosen according to type, for example to give a "J" or "K" or "T" or other type of thermocouple.

Preferably the thermocouple junction is directly attached onto the exposed die surface by bonding it thereto and this may be done using a thermally conductive adhesive. Alternatively the junction may be bonded to the die surface by fusing it thereto.

For a better understanding of the invention and to show how it may be carried into effect, embodiments thereof will now be described, by way of non- limiting example only, with reference to the accompanying drawings.

Brief Description of Drawings

Figure 1 shows a pre-existing IC device to be made into a temperature sensing IC device according to the invention.

Figures 2, 3 and 4 illustrate steps in a method for making a temperature sensing IC device according to an embodiment of the invention, using the device of Figure 1. Detailed Description

An integrated circuit device 10 which may be converted into a temperature sensing device according to the invention may be a SOIC (Small Outline Integrated Circuit) package (see Fig. 1 ) which includes a silicon die (or chip) 12 encapsulated within a plastic insulating material 14. Terminals 16 of the IC device 10 are connected by bond wires (not shown) to the circuitry formed within the die 12 and provide for electrical connections to be made to that circuitry.

In order to make a device according to the invention, at least a portion of the surface of die 12 is first exposed by a decapsulation process. In this process an area of the surface of device 10 over where the die 12 is thought to lie is heated and chemically etched, for example by being subjected to a controlled flow of fuming nitric or fuming sulphuric acid. The etching is continued until at least a portion of the surface of die 12 is exposed within a cavity 18 which extends out to an edge 20 of the device 10 (see Fig. 2). Care is required to ensure that most of the bond wires interconnecting the die 12 and the terminals 16 remain intact.

A thermocouple 22 is formed by fusing dissimilar thermocouple wires together into a small bead 24 (see Fig. 3 - the thermocouple wires are schematically represented by a single line) which provides the thermocouple junction. The fusing may be by spot welding. The thermocouple junction 24 is then attached directly onto the exposed top surface of die 12 using a thermally conductive adhesive. Prior to applying the thermally conductive adhesive the thermocouple 22 is preferably positioned within and along the base of cavity 18 and a cynoacrylate adhesive is applied at or near to the location 26 (see Fig.3) to hold the thermocouple 22 in position for the thermally conductive adhesive to be applied to the junction 24. Preferably the thermally conductive adhesive which is applied to attach junction 24 directly onto the surface of die 12 is XLN-589 manufactured by Mereco Technologies of West Warwick, R.I. 02893, USA. The junction 24 is held to the surface of die 12 and the adhesive is dripped onto it for the direct attachment to be made. For XLN-589 adhesive, maximum bond strength may be achieved by curing the adhesive at. 65°C for 4 hours, or at room temperature (25°C) for 48 hours.

After the thermally conductive adhesive at the junction 24 has cured, the removed encapsulating material 14 is replaced (that is, cavity 18 is filled) with an encapsulating or casting compound 28 having temperature characteristics as close as possible to those of the original material 14. A dispenser 30 may be used to inject the casting compound 28 into the cavity 18 until it is filled (see Fig. 4). A casting compound which is suitable for many IC devices is ECN-809 also manufactured by Mereco Technologies. This compound may be cured for 2 hours at 100°C. Excess hardened compound 28 is then removed by grinding to leave a flat surface as in the original device 10. This surface may then be cleaned and inked as desired.

A connector 32 is then preferably attached to the free ends of the thermocouple wires 22 for the thermocouple to be connected to a temperature measuring circuit or device. In this, the polarity of the two wires needs to be observed and the connector type matched to the type of thermocouple wires used (for example "J", or "K" or "T" type). A calibration characteristic for the temperature sensing IC device can then be determined.

It will be understood that the temperature calibration of a test handler will be undertaken using a temperature sensing IC device which corresponds to the type of IC devices to be handled and tested. Thus the method of the invention is applicable to many different types of IC devices including those types mentioned hereinbefore in the Background section along with others which are normally soaked to a set temperature within a handler preparatory to being electrically tested.

The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the scope of the following claims.

Claims

1. A temperature sensing integrated circuit device comprising a semi-conductor die embedded within encapsulating material, and a thermocouple having a junction which is directly attached to a surface of the die, wherein the thermocouple passes through the encapsulating material for connection to a temperature measuring circuit.

2. A temperature sensing integrated circuit device as claimed in claim 1 wherein the thermocouple comprises dissimilar metal wires which are welded together to form said junction.

3. A temperature sensing integrated circuit device as claimed in claim 2 wherein the thermocouple junction is directly attached to a surface of the die by being bonded thereto.

4. A temperature sensing integrated circuit device as claimed in claim 2 or claim 3 wherein the thermocouple junction is directly attached to a surface of the die by a thermally conductive adhesive.

5 A temperature sensing integrated circuit device as claimed in any one of claims 2, 3 or 4 wherein the thermocouple wires passing through the encapsulating material are embedded by the encapsulating material.

6. A temperature sensing integrated circuit device as claimed in any one of claims 2 to 5 wherein a connector is attached to the free ends of the thermocouple wires for connecting the thermocouple into a temperature measuring circuit.

7. A method of making a temperature sensing integrated circuit device comprising providing an integrated circuit device having a semi-conductor die embedded within encapsulating material, exposing at least a portion of a surface of the die by removing some of the encapsulating material, attaching a junction of a thermocouple directly onto said exposed die surface, and applying casting compound to replace said removed encapsulating material to re-encapsulate the die and the thermocouple passing through the encapsulation.

8. A method as claimed in claim 7 wherein at least a portion of the surface of the die is exposed by etching away the encapsulating material.

9. A method as claimed in claim 7 or claim 8 wherein the thermocouple comprises dissimilar metal wires which are welded together to form said junction, wherein the junction is directly attached to said exposed die surface by bonding it thereto.

10. A method as claimed in claim 9 wherein the junction is directly attached to said exposed die surface using a thermally conductive adhesive.