The present invention relates to an optoelectronic assembly and a method of making the same.
In many optoelectronic components and electronic components in general, these are provided with a housing, with the terminal contacts—also referred to as connection pins—arranged on a bottom side of the housing. For attachment to a printed circuit board, PCB, the electronic components are aligned with their housing and then placed on the PCB. In a subsequent soldering process, an existing solder is melted so that the individual terminal contacts on the underside of the housing are connected to corresponding terminal pads on the PCB. Depending on the manufacturing technique, a certain amount of solder is already present on the PCB or the underside of the housing, or this solder is provided during the soldering process.
However, depending on the housing geometry used and especially with very large terminal contacts on the underside of the housing, capillary and other effects can occur so that the housings are not symmetrically and parallel aligned with respect to the PCB. In addition to the resulting—in some applications—disadvantageous tilting, short circuits can also occur between individual terminal contacts on the underside of the housing. Reducing the amount of solder can help in some cases, but this cannot be reduced arbitrarily without causing contact problems or thermal coupling problems.
Accordingly, there is a need to provide housings that can be soldered sufficiently well regardless of the arrangement of the terminal contacts on the underside of the housing, so that the problems with regard to possible tilting or possible short circuits are reduced.
This need is met by the objects of the independent claims. Further developments and advantageous designs are the subject of the subclaims.
The inventors propose an optoelectronic assembly comprising a package and an electronic component disposed therein. The component may be an IC, an optoelectronic device, or a combination thereof. Multiple ICs, devices, or other elements may be housed within the package. The electronic component comprises two or more terminal contacts for supplying supply and/or control signals.
The housing may include a cover attached to a housing base. In some aspects, the housing is also integrally formed. The lower housing portion is formed with a planar textured lower housing surface. In accordance with the invention, the housing underside includes two or more solder contact pads each surrounded by a non-wettable region, the solder contact pads extending through the housing underside and being connected to the plurality of terminal contacts of the device. In addition, the housing bottom comprises two or more solder contact pads, each surrounded by a non-wettable region. In this regard, it is provided according to the invention that the solder contact pads and the solder areas are uniformly distributed on the underside of the housing so that there are no large whole-area areas that can be wetted by solder. By large whole-area areas are meant solder-wettable areas whose size is substantially larger than that of the other solder areas or solder contact pads and, in particular, occupies a large portion of the total area of the underside of the housing. In other words, the ratio of an area of a solder area or solder contact pad compared to the area of the underside of the housing is significantly smaller and is at most 45%. This ensures that the area of the bottom surface of the housing is divided into smaller areas, so that a solder material is distributed over a plurality of solder areas and solder contact pads that are separated from each other. This reduces the adverse effects mentioned at the beginning, or causes them along or in different parts of the underside of the housing, thereby compensating for each other.
Typical problems that occur when soldering assemblies for surface mounting are thus reduced or avoided altogether.
It should also be pointed out again at this point the difference between a solder area and a solder contact pad. Both surfaces basically serve to have solder material deposited on them in order to obtain, in some aspects, the most uniform distribution of solder material possible to compensate for the disadvantages mentioned at the beginning. However, a solder area has only a mechanical or thermal functionality, while a solder contact pad further comprises an electrical functionality. In other words, solder contact pads enable an electrical contact to a component on the other side, while the solder areas are either so-called blind areas or are only intended to form a contact to a reference potential. In addition, the solder areas can also serve a thermal, i.e. a transport of waste heat, so that they also transport away heat generated during operation in addition to the solder contact pads.
In some aspects, in order to achieve uniform and consistent positioning of the solder areas and the solder contact pads, it is provided that the underside of the housing is subdivided into a virtual grid of rows and columns. Thereby, according to the invention, a solder contact pad or a solder area is now arranged in a virtual grid field defined by the subdivision. Such a virtual subdivision is useful because it makes it particularly easy to achieve a uniform arrangement of the solder contact pads or the solder areas. In some aspects, the virtual grid fields formed in this manner are of equal size. However, it is also possible for rows and/or columns to be of different sizes, in which case it is convenient to select the grid fields of a row and/or column to be of equal size in each case. Furthermore, a certain symmetry of the raster field should be ensured, i.e. larger raster fields of a column should not be provided only along one edge of the bottom side of the housing. Different sizes of the grid fields are useful if solder areas and solder contact pads have different sizes.
In some aspects, an area of a virtual grid array comprises 1 to 1.75 times an area, in particular 1 to 1.4 times an area, of the solder area disposed in the virtual grid array and the surrounding non-wettable area or solder contact pad and the surrounding non-wettable area. In this context, each grid field either contains a respective solder area or solder contact pad with the respective non-wettable areas or is empty.
In some aspects, the two or more solder contact pads and the two or more solder areas each comprise the same size. However, it is also possible for them to be different sizes, while still being smaller than or equal to an area of a virtual grid array. In one aspect, it is provided that surfaces of the same size are arranged in the same row or the same column.
In another aspect, the shape and size of the solder contact pads is addressed. In some aspects, the two or more solder contact pads comprise the same shape. Similarly, the two or more solder contact pads may also comprise a different shape with respect to the solder contact pads. This may be appropriate when the solder areas are primarily for heat dissipation, but are not to carry current or other signals. In these aspects, the solder areas may also comprise a different size with respect to the solder contact pads. In another aspect, the solder contact pads are round and the solder areas are square.
In some aspects, the solder areas and the solder contact pads with their wettable area of a solder area or solder contact pad are significantly smaller than total area of the bottom surface of the housing. For example, the area of a solder area or solder contact pad may be in the range of 5% to 20%, but more particularly in the range of 7.5% to 15%, and most particularly in the range less than 12% of the total area of the underside of the housing.
In some aspects, the housing base includes a metallic layer on the underside of the housing as a heat sink. It may also be formed with a metallic block, or comprise a lead frame or similar metallic structure.
The two or more solder areas are then patterned on the underside of the housing. To this end, in some aspects, the solder areas may form protrusions formed by stamping, embossing, etching, or even via electroplating processes. In some aspects, the non-wettable regions surrounding the solder areas are formed with a solder resist. In other aspects, these areas are formed by removing the solder-wettable metal layer to expose a non-wettable layer. This can also be a metallic layer, but can also be an insulating layer.
In some aspects, the solder areas form a portion of the bottom surface of the housing. In such a case, they are planar with the package bottom surface and in some aspects comprise the same metal layer as the rest of the package bottom surface. In other aspects, the metal layer of the surface is formed by a thin gold layer only a few 10 nm or 100 nm thick. In the non-wettable areas surrounding the solder areas, the gold layer is removed. A special non-wettable layer may then be applied to these. Alternatively, the layer underlying the gold layer may comprise non-wettable properties such that liquid solder is repelled and attracts onto the solder area. Examples of this would be a solder-repellent metal, for example nickel, lying under the gold layer forming the surface.
In another aspect, the solder areas and/or the solder contact pads each comprise planar elevations extending across the underside of the housing. The non-wettable areas surrounding the solder areas are formed by the edge of the planar elevations, wherein optionally the metal layer wettable by solder, in particular gold, may be removed at the edge. Alternatively, a non-wettable material such as solder resist, glass or plastic can be adjacent to the edge. The planar protrusions may be in the range of 50 μm to 500 μm, particularly in the range of 100 μm to 300 μm. In aspects where the solder areas and or the solder contact pads are formed as elevations, the interstices may be formed with an insulating underfill material. this material may improve thermal coupling and be applied only after a soldering process. This prevents the soldering process from being impaired by the underfill material. At the same time, capillary effects can be exploited so that the underfill material flows into the gaps between the assembly and PCB after a soldering process.
Another aspect relates to a method of manufacturing such an assembly. In this, a housing having a planar housing underside and at least two solder contact pads arranged on the housing underside and surrounded by a non-wettable region is provided. The housing underside is subdivided into a plurality of first and second subregions, in particular subregions of equal size. The subdivision is such that a respective solder contact pad with the surrounding non-wettable region is located in a first of the plurality of subregions. In other words, the subregions can thus be defined as a function of the solder contact pads already present. Alternatively, these steps may be reversed so that the solder contact pads are formed in first previously defined sub-regions. The virtual grid areas described above can be understood as such partial areas.
Then, solder areas are created in second ones of the plurality of partial areas. Non-wettable areas are provided around the respective solder areas so that one solder area and the non-wettable area surrounding the solder area are each located within the respective second partial area. According to the invention, the first and second partial areas are substantially uniformly distributed on the underside of the housing.
In some aspects, it may be convenient to make the solder areas and the solder contact pads substantially equal in size, respectively. Similarly, no wettable area of a solder area or solder contact pad should exceed 40% of a total area of the bottom surface of the housing. In particular, the area of a solder area or solder contact pad may be within the ranges disclosed above.
In some aspects, the non-wettable regions around the solder areas and/or the solder contact pads are formed by forming a solder stop coating around the solder areas and/or solder contact pads. Alternatively, a glass layer may be provided around the solder contact pads. The solder contact pads may be contact pins surrounded by a glass cylinder and pass through the bottom of the housing. Further alternatively, the non-wettable areas around the solder pads and/or the solder contact pads may be formed removing the wettable metallic surface in the edge region around the solder pads and/or solder contact pads so as to expose an underlying non-wettable layer of the housing base.
In subsequent steps, the assembly is positioned on and soldered to a PCB. Then, in some aspects, a viscous underfill material can be applied around the assembly on the PCB so that it flows by capillary forces into gaps between the assembly and the PCB. This improves thermal coupling and prevents water or moisture accumulation in the interstices.
Further aspects and embodiments according to the proposed principle will become apparent with reference to the various embodiments and examples described in detail in connection with the accompanying drawings.
The following embodiments and examples show various aspects and their combinations according to the proposed principle. The embodiments and examples are not always to scale. Likewise, various elements may be shown enlarged or reduced in size to highlight individual aspects. It will be understood that the individual aspects and features of the embodiments and examples shown in the figures may be readily combined with each other without affecting the principle of the invention. Some aspects comprise a regular structure or shape. It should be noted that minor deviations from the ideal shape may occur in practice, but without contradicting the inventive idea.
In addition, the individual figures, features and aspects are not necessarily shown in the correct size, nor do the proportions between the individual elements have to be fundamentally correct. Some aspects and features are highlighted by showing them enlarged. However, terms such as “above”, “above”, “below”, “below”, “larger”, “smaller” and the like are correctly represented in relation to the elements in the figures. Thus, it is possible to derive such relationships between the elements based on the figures. However, the proposed principle is not limited herein, but different optoelectronic devices, with different size and also functionality can be used in the invention. In the embodiments, elements with the same or similar effects are shown with the same reference signs.
The glass 4 is guided together with the contact pin 3 through the lower housing part 100 and is guided inside the housing via one or more bonding wires 6 to terminal contacts of an electronic component 5. In the present embodiment, the electronic component 5 forms an edge-emitting reader which emits light towards the side in the direction of an outcoupling optics 7. In this respect, the housing cover 2 is thus provided with an opening in which the outcoupling optics 7 are arranged.
Depending on the embodiment, the underside of the housing 101 has a large surface area. This means that its total area is significantly larger than the area of the contact pin 3 formed by the solder contact pad 31.
In both embodiments, it is noticeable that the soldering areas 102 or 101 are shaped significantly differently in size from the respective solder contact pads. In a soldering process, this can lead to solder material accumulating primarily in the large-area region 102 or 101 due to capillary or other effects, resulting in tilting there. If, moreover, the component is only approximately positioned, as is quite common in conventional processes, and is then to “float in” via capillary effects of the solder, i.e. position itself correctly in a self-organizing manner due to the capillary effects, insufficient or even incorrect alignment may occur due to the different surfaces. In addition, it can happen that solder accumulating on one side leads to a short circuit.
The inventors therefore propose to provide approximately equally sized areas on a package underside to be wetted with solder to improve the process. Instead of the large-area underside of the housing shown in
In
This improves floating of the assembly in liquid solder due to the capillary forces present and positions it on the corresponding contacts of the PCB in a self-organizing manner. At the same time, tilting due to an accumulation of larger amounts of solder on one side is reduced.
In addition, there are several solder contact pads 31, each of which is surrounded by a non-wettable area 4. The solder contact pads 31 form the surface of the terminal contacts 3 which lead into the interior of the housing and are connected there to the terminal contacts of the electronic component. Like the soldering areas 110, contact areas 31 can be produced galvanically or in another way.
The solder contact pads 31 are guided through the lower housing part 100 via contact pins, i.e. feedthroughs, and are guided inside the housing to terminal contacts of an electronic component via one or more bonding wires. In this way, the solder contact pads 31 contact a component mounted on the other side. In contrast, the solder areas 110 are designed as so-called blind solder areas, i.e. they do not assume any electrical or electronic function with respect to the component on the other side. However, as already explained, they can be used to dissipate some of the heat generated during operation.
As shown in the lower partial figure of
In the embodiment example of
In a further embodiment, an additional solder resist can be provided between the individual solder areas 110 or also the adjacent non-wettable areas 4. Such an arrangement is shown in
To create and produce the individual solder areas 110, an area between the underside of the housing and the solder areas 110 is now slightly removed, resulting in the edge areas 130 shown in
In an alternative aspect, during fabrication of the housing according to the invention, the bottom surface 101 of the housing is covered with a photomask, patterned, and the corresponding solder areas 110 are coated with gold or other material wettable by solder. Subsequently, after a removal of the photomask, the surrounding areas 130 are created using a laser writing process or other processes. In such an embodiment, the solder areas 110 would thus form low elevations based on the deposition process of the bottom surface 101 of the housing. The surrounding areas represent the edges of these areas 110.
In the previous embodiments, a certain symmetry is provided by the distribution of the solder areas and the solder contact pads due to the subdivision of the grid. In a corresponding soldering process, tilting or other interference is avoided by subdividing the entire underside of the housing into various individual areas to be soldered. However, it is also possible to arrange the individual solder contact pads not in a line, but at different positions depending on requirements and design.
For uniform distribution according to the proposed principle, in step S2 the underside of the housing is subdivided into a grid consisting of a plurality of virtual grid fields or subareas, in particular grid fields or subareas of equal size. The subdivision is carried out in such a way that already existing solder contact pads with the surrounding non-wettable area lie in first grid fields.
Subsequently, in step S3, solder areas are generated in second grid fields and these are surrounded by a non-wettable area in step S4. This is done in such a way that the generated solder area and the non-wettable area surrounding the solder area lie within the respective grid field. In this way, grid fields are covered with solder areas and solder contact pads, so that areas to be soldered are essentially uniformly distributed on the underside of the housing.
Number | Date | Country | Kind |
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10 2021 112 740.8 | May 2021 | DE | national |
The present application is a national stage entry from International Application No. PCT/EP2022/063299, filed on May 17, 2022, published as International Publication No. WO 2022/243298 A1 on Nov. 24, 2022, and claims the priority of German application DE 10 2021 112 740.8 filed May 17, 2021, the disclosure content of all of which are hereby incorporated by reference in their entireties.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2022/063299 | 5/17/2022 | WO |