GB2440971A

GB2440971A - Soldering oven

Info

Publication number: GB2440971A
Application number: GB0616024A
Authority: GB
Inventors: Wilibald Konrath; Klaus Scholl; Helmut Greiner
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2006-08-14
Filing date: 2006-08-14
Publication date: 2008-02-20
Also published as: GB0616024D0

Abstract

A soldering oven apparatus (200) for assembling electronic components (106) in a process of attaching said components (106) to a substrate (104) comprising a quartz lamp heat source (206) and a platform (202) located above the heat source (206) and adapted to receive a boat (102) with said components (106) pre-assembled on said substrate (104), wherein the platform (202) comprises at least one cut-out (204) of a shape substantially similar to the shape of the boat (102) and further adapted to receive the boat (102) above the cut-out (204).

Description

APPARATUS FOR ASSEMBLING ELECTRONIC COMPONENTS

Field of the Invention

The present invention relates to assembling electronic components. in general, and in particular to an apparatus for assembling electronic components of microwave hybrid modules.

Backaround of the Invention

Within microwave hybrid modules at microwave and millimetre wave frequencies Gallium-Arsenide MMICs (Microwave Monolithic integrated Circuit) are used veiy often. Key advantages are extremely high circuit integration and a consistent RF performance. Possible die attach methods are AuSn-soldering or various epoxy attach processes using conductive adhesive, e.g. epoxy dispense or epoxy stamp printing. AuS n-soldering is often preferred for applications with high power dissipation.

Known solutions use hermetically sealing of Micro-Electro-Mechanical-Switch (MEMS) elements on wafer-level with e.g. pre-tinned silicon caps.

Conventionally, such circuit modules are assembled in automatic manufacturing lines using so-called boats, flat carrier plates whose external shape is adapted so as to allow for a steady and safe transport on a conveyor device of the assembly line, and which are used to mount thereon a baseplate on which the circuit components of a finished circuit module will be fixed directly or indirectly.

An example for such a conventional boat is shown in a plan view in Fig. 1. The space available on such a boat I for fixing a baseplate 2 is limited, so that when manufacturing RF hybrid circuits only circuit components which actually process a RF signal are arranged on the baseplate 2 and circuit components processing lower frequency signals, providing supply voltages for the RF hybrid circuit, etc., are usually located outside the baseplate 2.

An alternative boat design is known for example from European patent EP1464211B1 where the boat and baseplate are integrated in one element.

Physical connection of the components to a substrate is caused by melting the solder by a heat transfer in an oven, where the boat with the substrate and the components to be assembled is placed.

In solutions known in the art a solder oven has an aluminum or silicon-carbide oven plate or platform, which is sitting directly above an array of high power quartz lamps. The quartz lamps radiate their power towards this oven platform. The components to be soldered at 320 C (in case of AuSn solder) are positioned on top of that plate. Final heat transfer into these components is performed by mechanical contact to the oven platform. For that purpose the boat with the pm-assembled components goes through the oven by an integrated handling robot. The robot puts a boat into the oven, the oven closes automatically, the desired solder process is performed, the oven opens automatically and the robot moves the boat towards a cooling station and finally a magazine un-loader.

A batch of components, e.g. 100 loose stacked "sandwiches" consisting of a metal shim, a solder preform and a GaAs-MMIC chip are positioned on that boat using a pick & place assembly machine. Afterwards the boat is running downstream through the assembly cell, picked up by the handling robot and taken into the solder oven. The whole process is vibration-free up to this point.

A disadvantage of the solutions known in the art is that the large oven plate sitting above the quartz lamps gets unavoidably bowed (deformed) being heated up to a temperature of 320 C. This is especially a problem of very large plates, approximately l0"xlO". The result is that the boats are floating during solder process. The gas flow through the oven (e.g. nitrogen and forming gas) additionally supports the floating of the boats due to an air cushion effect (small air gap between the two plates beginning to bow). The whole process in terms of movement and vibration of the components gets out of control. Finally the position of the boats at the end of the soldering process in many cases does not match the programmed gripper positions of the handling robot. As a result of that the boat cannot be gripped at the end of the soldering process because the robot could crash with the boat. Additionally, due to the vibrations caused by the gas flow and the air-cushion effect, positions of the components on the substrate may change from the programmed ones and the resulting quality of the soldering process is dangerously lowered.

Hence, an improved apparatus for assembling electronic components would be advantageous and in particular one that is not sensitive to some deformation of the platform caused by the heat and that keep the boat and consequently the substrate and components in a stable and vibration-free position during the soldering process.

Sunmiarv of the Invention Accordingly, the invention seeks to preferably mitigate, alleviate or eliminate one or more of the disadvantages mentioned above singly or in any combination.

According to a first aspect of the present invention, as defined in claim 1, there is provided an apparatus for assembling electronic components in a process of attaching said components to a substrate. The apparatus comprises a heat source and a platform located above the heat source and adapted to receive a boat with said components pre-assembled on said substrate. The platform comprises at least one cut-out of a shape substantially similar to the shape of the boat and is further adapted to receive the boat above the cut-out.

Preferably the apparatus comprises three studs located on the platform along edges of the cut-out for providing support for the boat when placed on the platform.

Optionally the height of the studs is adjustable.

Preferably the boat has a non-reflective bottom surface, which, preferably, is black anodised.

Further features of the present invention are as claimed in the dependent claims.

The present invention beneficially allows for even heat distribution throughout the boat, which in turn ensures that the solder or conductive adhesive used in the assembly process is also evenly heated and melted to form required electric connection between the components and the substrate. Additionally, the three-point suspension on the studs eliminates the negative effects of deformation of the platform caused by the heat and by placing the boat at some distance above the platform a gap is formed between the platform and the boat. The gap allows for undisturbed flow of the gas in the oven chamber and prevents formation of an air-cushion underneath the boat. As a result of that the uncontrolled movements and vibrations of the boat caused by bowing, gas flow and air-cushioning are eliminated or at least alleviated.

Brief description of the drawings

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: FIG. 1 is a diagram illustrating a boat used in an assembly process; FIG. 2 is a diagram illustrating apparatus for assembling electronic components in one embodiment of the present invention; FIG. 3 is a diagram illustrating apparatus for assembling electronic components with a boat placed in its operation location in one embodiment of the present invention.

Description of embodiments of the invention

With reference to FIG. 2 and FIG. 3 a soldering oven 200 is presented. For the sake of clarity the drawings present the invention in a very schematic way with elements and lines not essential for understanding the invention omitted.

In the presented embodiment the soldering oven 200 for attaching electronic components 106 to a substrate 104 comprises a heat source 206 and a platform 202 located above the heat source 206. In an automated production process the electronic components are placed on correct positions of the substrate 104 by a pick-and-place robot and such pre-assembled module is transported on the boat 102 by a conveyor to the soldering oven. The function of the boat was already explained in the background section and illustrated in FIG. 1 and therefore will not be repeated in this section. The platform 202 is adapted to receive the boat 102 with said components 106 pre-assembled on said substrate 104. The platform 202 comprises at least one cut-out 204 of a shape substantially similar to the shape of the boat 102 and the boat 102 with the substrate 104 and the elements 106 is placed by another pick-and-place robot or other transport device above the cut-out 204. It is within contemplation of the present invention that the platform 202 may comprise more than one cut-outs, which is illustrated, for example, in FIG. 2 and FIG. 3.

In an alternative embodiment the oven 200 comprises three studs 208 located on the platform 202 along edges of the Cut-out 204. The three studs 208 provide very stable support for the boat 102 when placed on the platform.

By having the cut-Out 204 it is possible to transfer the heat directly 304 from the heat source 206, which in one embodiment is an array of quartz lamps, to the boat 102 and further to the solder used for connecting the electronic elements 106 to the substrate 104. It is however within contemplation of the present invention that other heat sources also can be used or that instead of array of the quartz lamps only one quartz lamp is installed. This direct transfer significantly improves the soldering process as even if the platform or the boat is deformed as a result of the heating the transfer of heat is still uniform. Placing the boat on the three studs 208 has the benefit that even if the platform or the boat is bowed it is still supported in these three points, which ensures stable location of the boat and consequently the electronic components during the soldering process. Additionally by using the studs 208 it is possible to have undisturbed flow 302 of gas (nitrogen or forming gas) in the area of the heat source 206 and the boat 102, which, in turn, eliminates an air-cushion effect responsible for unwanted vibrations in the solutions known in the art.

In yet another alternative embodiment the studs 208 have adjustable height. This allows for controlling the heat and gas flow.

In one embodiment the boat 102 has a non-reflective bottom surface in order to improve effectiveness of the heat transfer and in an preferred embodiment the bottom io surface of the boat 102 is black anodised.

Although the invention is described above as based on the example of soldering (e.g. using gold-tin (AuSn) solder) it is also applicable if the process of attaching includes epoxy attach processes using conductive adhesive.

Claims

CLAIMS

1. An apparatus (200) for assembling electronic components (106) in a process of attaching said components (106) to a substrate (104) comprising a heat source (206) and a platform (202) located above the heat source (206) and adapted to receive a boat (102) with said components (106) pre-assembled on said substrate (104), wherein the platform (202) comprises at least one cut-out (204) of a shape substantially similar to the shape of the boat (102) and further adapted to receive the boat (102) above the cut-out (204).

2. The apparatus (200) according to claim 1 comprising three studs (208) located on the platform (202) along edges of the cut-out (204) for providing support for the boat (102) when placed on the platform.

3. The apparatus (200) according to claim 2, wherein the studs (208) have adjustable height.

4. The apparatus (200) according to any one of preceding claims, wherein the heat source (206) is at least one quartz lamp.

5. The apparatus (200) according to any one of preceding claims, wherein the boat (102) has a non-reflective bottom surface.

6. The apparatus (200) according to claim 5, wherein the bottom surface of the boat (102) is black anodised.

7. The apparatus (200) according to any one of preceding claims, wherein said process of attaching includes one of soldering or epoxy attach processes using conductive adhesive.

8. An apparatus for assembling electronic components in a process of attaching said components to a substrate substantially as hereinbefore described with reference to FIG. 2 and FIG. 3 of the accompanying drawings.