Patent Description:
Semiconductor dies may be bonded to a substrate in a press sintering process, although a press sintering process is not restricted to only semiconductor dies and underlying substrates, for instance, to achieve a high heat conductivity from the semiconductor product to the substrate. Sintering of bonds from high conductive metals like silver or copper is done at elevated temperatures, typically in the range of <NUM> - <NUM>, while a pressure is applied onto the product that is sinter bonded to its underlying substrate. Parts of the product(s) to be sintered which have not been coated with a protective coating will oxidize rapidly at these elevated temperatures. Copper, for instance, will oxidize in complex oxides which are difficult to remove at a later moment in the process. These oxides causes quality problems at subsequent processes like wire bonding.

Another issue is that contaminants are released from the sintering materials, like in sintering pastes and films, at the elevated temperatures during the sintering process, which generally gives rise to contamination of the products as well.

A commonly used method is to create a protective atmosphere with an inert gas like nitrogen. This is done in an enclosed process chamber, or in multiple process chambers which are interconnected with airtight gates between them. A sintering process commonly has three phases: a preheating stage of the product to be sintered, the actual sintering stage, and cooling the product down to room temperature again. These phases can be done in one process chamber or in separated chambers. In both cases the atmosphere must be changed each cycle, which is done by evacuating the chamber and introducing the inert gas into the chamber. Each chamber requires an atmosphere change, in case the three phases are done in three separate chambers, thus requiring a three-time atmosphere change.

The atmosphere change takes quite a long time since the volume of the process chambers is rather large. Therefore, the cycle times of the known sintering systems and processes are must longer than required for the actual sintering processes itself.

<CIT> discloses a sintering process product carrier according to the state of the art for carrying at least one product to be sintered in a sintering process.

It is an objective of the invention to allow for a press sintering process and apparatus with a reduced cycle time.

It is another or alternative objective of the invention to allow for a press sintering process and apparatus that provides for a reduced contamination level.

It is yet another or alternative objective of the invention to allow for a press sintering process and apparatus which do not present undesired chemical reactions, especially oxidation, during the sintering process.

It is yet another or alternative objective of the invention to allow using a reduced amount of inert gas in the press sintering process and apparatus.

At least one of the above objectives is achieved by a press sintering process product carrier for carrying at least one product to be sintered in a press sintering process, the product carrier comprising.

In stead of moving the products to be sintered from chamber to chamber and changing atmosphere each phase, the products are placed in a moveable product carrier in which a protective atmosphere is created only once at the start of the first phase. This protective atmosphere can be maintained each phase until the product is cooled down to room temperature. The product carrier passes through all three phases of the sintering process and can then be passed back to the start of the first phase.

The protective atmosphere in the small product receiving recess is created by closing the recess by a film, foil or sheet of material after product placement to provide a recess chamber, and flushing the small recess chamber with an inert gas like nitrogen. The volume of the recess chamber need only to be somewhat larger than the volume of the product to be sintered. The recess chamber is closed with a film, foil or sheet of, for instance, Teflon, which is held by a vacuum to ensure good closure of the recess chamber. At one side inside the chamber the inert gas is inserted thru multiple holes and pushes the entrapped air in the chamber thru exhaust holes at opposite side. These exhaust holes are located at lower level than flush holes to ensure all air is pushed out of the small chamber, air is heavier than nitrogen.

In an embodiment the top side surface is planar.

In an embodiment the top side surface fully surrounds the product receiving recess.

In an embodiment the holding groove fully surrounds the product receiving recess.

In an embodiment the recess gas inlet is provided at a first side of the product receiving recess and the recess gas outlet is provided at a second side of the product receiving recess, the second side opposing the first side.

In an embodiment the recess gas inlet comprises a plurality of gas inlet openings distributed along a side of the product receiving recess, the gas inlet openings being arranged for providing, in use, an outflow of gas from the gas inlet openings in a direction of the product(s) carried on the recess bottom.

In an embodiment the plurality of gas inlet openings is configured to provide, in use, a laminar flow of gas.

In an embodiment the recess gas outlet comprises a plurality of gas outlet openings distributed along a side of the product receiving recess.

In an embodiment the recess gas outlet is provided at a lower level with respect to an, in use, horizontal plane than the recess gas inlet.

In an embodiment an additional recess is provided in the recess bottom at a side of the product receiving recess where the recess gas outlet is provided.

In an embodiment the vacuum connection is provided at a position on the product carrier such that the holding groove is in between the product receiving recess and the vacuum connection as seen along external surfaces of the product carrier, optionally the vacuum connection being provided on a side surface of the product carrier.

In an embodiment the product carrier comprises a first gas connection for connection to a gas source, the first gas connection being in fluid connection with the recess gas inlet and being provided at a position on the product carrier such that the holding groove is in between the product receiving recess and the first gas connection as seen along external surfaces of the product carrier, optionally the first gas connection being provided on a side surface of the product carrier.

In an embodiment the product carrier comprises a second gas connection for connection to a gas drain, such as a pump, the second gas connection being in fluid connection with the recess gas outlet and being provided at a position on the product carrier such that the holding groove is in between the product receiving recess and the second gas connection as seen along external surfaces of the product carrier, optionally the second gas connection being provided on a side surface of the product carrier.

In an embodiment the product carrier further comprises at least one of an arrangement for cooling the product carrier and the product(s) carried thereby, and an arrangement for heating the product carrier and the product(s) carried thereby.

In an embodiment the product carrier further comprises a flexible cover, such as a film, foil or sheet of material, for covering the product receiving recess and the holding groove.

Another embodiment of the invention provides for a kit of a product carrier as referred to above and a flexible cover, such as a film, foil or sheet of material, configured for covering the product receiving recess and the holding groove.

Another embodiment of the invention provides for a sintering apparatus comprising a product carrier as referred to above.

In another aspect the invention provides for a press sintering process comprising the steps of.

Further features and advantages of the invention will become apparent from the description of the invention by way of non-limiting and non-exclusive embodiments. These embodiments are not to be construed as limiting the scope of protection. The person skilled in the art will realize that other alternatives and equivalent embodiments of the invention can be conceived and reduced to practice without departing from the scope of the present invention. Embodiments of the invention will be described with reference to the accompanying drawings, in which like or same reference symbols denote like, same or corresponding parts, and in which.

The sintering apparatus <NUM>, and corresponding sintering process, schematically shown in <FIG> provides an input conveyer <NUM> for receiving one or more products P to be sintered. The products are then transferred to a press sintering process product carrier <NUM> according to the invention in the press sintering apparatus <NUM> for further processing in the sintering apparatus. Alternatively, the one or more products P can be provided onto the press sintering process product carrier <NUM> (further referred to as product carrier) first and subsequently be transferred to the input conveyer <NUM>, after which the product carrier <NUM> according to the invention, together with the one or more products carried thereon, is transferred into the sintering apparatus <NUM> for further processing therein. In a first stage <NUM> the product carrier <NUM> with product(s) P is preheated and subsequently transferred to a press sintering stage <NUM> for further heating and applying pressure onto the product(s) P. <FIG> shows the product carrier <NUM> below a pressure block <NUM> of the press sintering stage <NUM>. The pressure block is to exert a pressure onto the products P to be sintered. The pressure block shown has a product dependable movable insert <NUM> that can be lowered from the pressure block <NUM> to exert pressure onto the product(s) P. The block may also have fixed protruding inserts. More than one insert <NUM> can be present. The number of inserts <NUM> may correspond to the number of products P carried on the product carrier <NUM>. In yet other embodiments of the pressure block, a larger pressure block with a flat bottom side can be provided to exert pressure onto one or more products, optionally with a resilient and or compliant material, like a silicone mat, between pressure block and product(s). Various embodiments are available in that regard. After press sintering in the sintering stage <NUM>, the product carrier <NUM> with product(s) P is transferred to a cool down stage <NUM> for cooling down the product carrier and products thereon. Subsequently, the individual products P are transferred to an output conveyer <NUM>, or the product carrier <NUM> with product(s) thereon is transferred to the output conveyer <NUM> for further handling.

<FIG> shows a perspective view of the product carrier <NUM> in more detail. <FIG> show different perspective views of the product carrier with multiple products P carried thereon. The product carrier comprises a top side <NUM> for carrying the one or more products P thereon. The products are carried such on the product carrier that they can be accessed in the sintering process by the (movable) insert(s) <NUM>. A product receiving recess <NUM> is defined in the top side <NUM> of the product carrier. The product receiving recess <NUM> is configured for receiving the one or more products therein and for carrying the product(s) on a recess bottom <NUM> of the product receiving recess. A planar top surface <NUM> surrounds the product receiving recess <NUM>. A holding groove <NUM> is provided in the top surface <NUM> and surrounds the product receiving recess <NUM>. Both the top side surface <NUM> and the holding groove <NUM> fully surround the product receiving recess <NUM> in the embodiment shown. A top side surface part <NUM> of the top side surface <NUM> is located in between the product receiving recess <NUM> and the holding groove <NUM>, and another top side surface part <NUM> is located at the outside perimeter side of the holding groove <NUM>.

A vacuum connection <NUM> is provided on the product carrier in fluid connection with the holding groove <NUM> to allow providing a vacuum in the holding groove for holding a flexible cover, such as a film, foil or sheet of material, provided over the product receiving recess <NUM> and the groove <NUM>. <FIG> show the outline of the cover in the form of a sheet S of Teflon in the embodiment shown, which can be provided over the product receiving recess <NUM> and holding groove <NUM>. <FIG> shows the sheet S of Teflon in place. A vacuum provided in the holding groove <NUM> acts to hold the sheet S onto the top side surface <NUM> and over the product receiving recess <NUM>. A pump (not shown) can be connected to the vacuum connection <NUM> for generating the vacuum. Ducts are manufactured in the product carrier to provide for the fluid connection between the holding groove <NUM> and the vacuum connection <NUM>. The vacuum connection <NUM> is provided at a position on the product carrier <NUM> such that the holding groove <NUM> is in between the product receiving recess <NUM> and the vacuum connection as seen along external surfaces of the product carrier. The vacuum connection <NUM> is provided on a side surface <NUM> at the front of the product carrier <NUM> in the embodiment shown.

The product carrier <NUM> further has a recess gas inlet <NUM> arranged in the product receiving recess <NUM> for introducing a gas into the product receiving recess, and a recess gas outlet <NUM> arranged in the product receiving recess for extracting gas from the product receiving recess. The recess gas inlet <NUM> is provided at a first side <NUM> of the product receiving recess <NUM> and the recess gas outlet <NUM> is provided at a second side <NUM> of the product receiving recess. The second side <NUM> opposes the first side <NUM> of the product receiving recess <NUM>. In use, a flow of gas will therefore be provided from the recess gas inlet <NUM>, passing the products P to the recess gas outlet <NUM> to purge the product receiving recess. Any contamination generated during the sintering process will thus be carried away from the products with the flow of gas.

The recess gas inlet <NUM> comprises a plurality of gas inlet openings <NUM> distributed along the first side <NUM> of the product receiving recess <NUM>. The gas inlet openings are distributed over the full first side <NUM>. The gas inlet openings <NUM> are provided such as to provide, in use, an outflow of gas from the gas inlet openings in a direction of the products P carried on the recess bottom <NUM> in the product receiving recess <NUM>, and are configured to provide a laminar flow of gas. On the opposing second side <NUM> of the product receiving recess <NUM>, the recess gas outlet <NUM> comprises a plurality of gas outlet openings <NUM> distributed along the second side. The gas outlet openings <NUM> are distributed over the full second side <NUM>.

The recess bottom <NUM> is largely planar to be provided, in use, along a horizontal plane in the sintering process. The products P are generally provided at some distance above the recess bottom on protrusions extending from the recess bottom <NUM>. A top side of the products P carried in the product receiving recess <NUM> is generally below the top side surface <NUM>, so there will some distance between the products and the flexible cover in the form of the sheet S of, for instance, Teflon, provided over the product receiving recess <NUM>. The flow of gas will pass over, under and alongside the products P from the recess gas inlet <NUM> to the recess gas outlet <NUM> to entrain any contamination from the products. The recess gas outlet <NUM> is provided at a lower level with respect to the horizontal plane than the recess gas inlet <NUM>. Oxygen is heavier than a generally used purging gas, such as nitrogen, to provide for a gas flow from the recess gas inlet <NUM> to the recess gas outlet <NUM>. The recess gas outlet <NUM> being at a lower level than the recess gas inlet <NUM> ensures that the heavier oxygen accumulates at the lower level and is efficiently removed from the product receiving recess <NUM>. An additional recess <NUM> is provided in the recess bottom <NUM> at the second side <NUM> of the product receiving recess <NUM>, to allow the recess gas outlet <NUM> to be provided at the lower level.

The product carrier <NUM> comprises a first gas connection <NUM> for connection to a gas source of purging gas. The first gas connection <NUM> is in fluid connection with the recess gas inlet <NUM> by ducts provided in the product carrier <NUM>. The first gas connection <NUM> is provided at a position on the product carrier such that the holding groove <NUM> is in between the product receiving recess <NUM> and the first gas connection as seen along external surfaces of the product carrier. In the embodiment shown, the first gas connection <NUM> is provided on a side surface <NUM> at the front of the product carrier. The figures show that first and second product carrier parts <NUM>, <NUM> are present to allow manufacturing the fluid connection providing ducts from the first gas connection <NUM> to the recess gas inlet <NUM>.

The product carrier <NUM> comprises a second gas connection <NUM>, 165A for connection to a gas drain. The second gas connection <NUM>, 165A is in fluid connection with the recess gas outlet <NUM> through ducts provided in the product carrier. The second gas connection <NUM>, 165A is provided at a position on the product carrier such that the holding groove <NUM> is in between the product receiving recess <NUM> and the second gas connection as seen along external surfaces of the product carrier. The figures show two types of second gas connection <NUM>, 165A. In a first variant of the second gas connection <NUM> the purging gas is allowed to flow out from the second gas connection <NUM> into the ambient surroundings at ambient pressure. A purging gas flow will be present inside the product receiving recess <NUM> when the pressure of the gas at the first gas connection <NUM> is higher than ambient pressure. The ambient surroundings act as a gas drain. In a second variant of the second gas connection 165A, a third product carrier part <NUM> is provided with internal ducts to provide for fluid connection of the second gas connection 165A with the recess gas outlet <NUM>. The second variant of the second gas connection 165A allows for connection to a pump to pump away the purging gas. The third product carrier part <NUM> is shown in dashed lines as an optional part in the drawings.

As described above with reference to <FIG> and <FIG>, one or more products P to be sintered are to be provided in the product receiving recess <NUM> of the sintering process product carrier <NUM> in the overall sintering process. A flexible cover, such as a film, foil or sheet S of material, for instance a sheet S of Teflon, is provided over the product receiving recess <NUM> and holding groove <NUM>, and a vacuum is applied to the holding groove to hold the sheet S on the top side surface of the product carrier. A purging gas source, such as a source of nitrogen is connected to the first gas connection <NUM> to allow for a flow of purge gas in the product receiving space <NUM>. A pump may be connected to second gas connection 165A or the purge gas may be allowed to flow out of second gas connection <NUM> into the ambient surroundings. Subsequently, the product(s) carried in the product carrier are processed in the processing stages as has been described with reference to <FIG> and <FIG> above. The flexible cover provided over the product receiving recess <NUM> still allows applying a pressure onto the products P by the (movable) inserts <NUM>. The inserts apply a pressure onto the product(s) while the flexible cover is in between insert and product.

Claim 1:
A press sintering process product carrier (<NUM>) for carrying at least one product (P) to be sintered in a press sintering process, the product carrier comprising
- a top side (<NUM>);
- a product receiving recess (<NUM>) defined in the top side, and configured for receiving the product(s) therein and for carrying the product(s) on a recess bottom (<NUM>) of the product receiving recess;
- a top side surface (<NUM>) surrounding the product receiving recess;
- a holding groove (<NUM>) provided in the top side surface and surrounding the product receiving recess, and a vacuum connection (<NUM>) in fluid connection with the holding groove to allow providing a vacuum in the holding groove for holding a flexible cover, such as a film, foil or sheet (S) of material, provided over the product receiving recess and the holding groove; and
- a recess gas inlet (<NUM>) arranged in the product receiving recess for introducing a gas into the product receiving recess, and a recess gas outlet (<NUM>) arranged in the product receiving recess for extracting gas from the product receiving recess to allow providing a flow of gas from the recess gas inlet to the recess gas outlet for purging the product receiving recess.