Carrier system for preventing silicon wafer pollution in a reflow oven

Abstract

The application provides a carrier system for preventing silicon light sheet pollution in a reflow oven, which is used for carrying integrated chips with through holes in the middle, so that the integrated chips can be reflow soldered in the convection reflow oven. The carrier system comprises a convection carrier and a silicon light sheet protection cover. The convection carrier is provided with a plurality of linearly arranged chip carrying positions, and the positions avoiding the silicon light sheet. The silicon light sheet protection cover is in a U shape, clamps the integrated chip through the through hole to the position on the side of the silicon light sheet, and contains the silicon light sheet. The upper branch of the silicon light sheet protection cover is provided with an inclined upper air guide grille. The lower branch of the silicon light sheet protection cover is provided with a lower air guide grille. The carrier system for preventing silicon light sheet pollution in a reflow oven provided by the application can prevent particles from staying on the surface of the silicon light sheet, and even if there are particles, the particles can be blown away by the inclined air flow. That is, the silicon light sheet protection cover structure provided by the application can make the silicon light sheet cleaner before reflow soldering.

Description

Technical Field

[0001] This invention relates to the field of chip manufacturing, and in particular to a carrier system for preventing silicon wafer contamination in a reflow oven. Background Technology

[0002] Reflow ovens are commonly used equipment in chip manufacturing, playing a crucial role, especially in PCB assembly. There are two common types of reflow ovens: vacuum reflow ovens and open reflow ovens. Vacuum reflow ovens ensure high-precision reflow heating of products without contaminating the chips. For the carrier structure of vacuum reflow ovens, for example, the DBC and chip vacuum reflow soldering fixture disclosed in patent publication number CN219892169U can simultaneously hold multiple chips. Open reflow oven structures also require specially designed carriers, and the chips are heated by a high-temperature airflow.

[0003] refer to Figure 1 Our company currently produces an integrated chip 10 with a through-hole 11 in the middle, and a silicon photodiode 12 is also provided on one side of the through-hole 11. Due to the structural characteristics of this chip, the reflow soldering effect using a vacuum reflow oven is not good. However, if the integrated chip 10 is placed in an open reflow oven for reflow soldering, when the high-temperature airflow blows onto the silicon photodiode 12 on the integrated chip 10, the dust and particles contained in the airflow will remain on the surface of the silicon photodiode 12, resulting in contamination of the silicon photodiode 12. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide a carrier system for preventing silicon wafer contamination in a reflow oven, thereby solving the problem of silicon wafer surface being contaminated by particulate matter in the airflow during the heating process of integrated chips, and at the same time avoiding the problem of uneven heating of the integrated chips on both sides due to the protection of silicon wafers.

[0005] To address the aforementioned technical problems, this invention provides a carrier system for preventing silicon photonics wafer contamination in a reflow oven. This system supports integrated chips with through-holes in the center, enabling them to be reflow soldered in a convection reflow oven. It includes a convection carrier and a silicon photonics wafer protection cover. The convection carrier has several linearly arranged chip support positions, avoiding the silicon photonics wafer. The silicon photonics wafer protection cover is U-shaped, clamping the integrated chip through the through-holes towards the silicon photonics wafer and housing the wafer within it. Corresponding to the upper surface of the integrated chip with the silicon photonics wafer, the upper arm of the silicon photonics wafer protection cover has an inclined upper air guide grille, with an air gap maintained between the bottom of the upper air guide grille and the silicon photonics wafer to allow airflow. Corresponding to the lower surface of the integrated chip without the silicon photonics wafer, the lower arm of the silicon photonics wafer protection cover has a lower air guide grille.

[0006] The upper support arm of the silicon wafer protective cover is provided with an air outlet at its end, which is used to guide the airflow that is blown toward the silicon wafer through the upper air guide grille; the air outlet also serves as the insertion port for the silicon wafer, and its height is higher than that of the silicon wafer, so as to avoid the silicon wafer during the insertion of the silicon wafer protective cover.

[0007] The upper support arms on both sides of the air guide outlet directly abut against the surface of the integrated chip to block the airflow from both sides, forcing the airflow to be discharged from the air guide outlet, while also providing a larger support area.

[0008] The upper air guide grille is sloping or curved.

[0009] The lower air guide grille is perpendicular to the surface of the integrated chip, and the direction of the lower air guide grille is arranged longitudinally.

[0010] The chip carrier positions on the convection carrier are arranged horizontally and have a concave design, with longitudinal connecting ribs formed between adjacent chip carrier positions.

[0011] Each chip carrier position has a horizontally arranged chip carrier platform in the middle, and on both sides of the chip carrier platform are airflow ports with edges extending beyond the outline of the integrated chip: an upper airflow port and a lower airflow port; the integrated chip is installed after the chip carrier position, and there is a vertical gap between the edge of the integrated chip and the upper and lower airflow ports to allow convective airflow to pass through.

[0012] The connection between the chip carrier and the connecting ribs on both sides is also provided with a recessed air guide groove to allow airflow between the upper and lower air outlets.

[0013] The upper air inlet has inwardly protruding upper support blocks on both sides; the lower air inlet has inwardly protruding lower support blocks on both sides.

[0014] The chip carrier platform is provided with a chip limiting protrusion. The size of the chip limiting protrusion is smaller than the size of the through hole, and the chip limiting protrusion avoids the silicon photodiode protective cover. That is, the chip limiting protrusion and the silicon photodiode are positioned with a gap to allow the chip limiting protrusion to not interfere with the silicon photodiode protective cover after it is installed.

[0015] This invention provides a silicon photocell protective cover that ensures convection and cleans the silicon photocell. The protective cover is U-shaped, and when placed horizontally, it forms a horizontal clamp in the middle. It includes an upper arm and a lower arm. The upper arm has an upper air guide grille arranged from top to bottom, and the lower arm has a lower air guide grille arranged vertically. The upper arm has an air outlet at the opening, and the upper air guide grille inside the air outlet forms a concave receiving space to accommodate the silicon photocell. The lower air guide grille of the lower arm is connected to a first air guide port near the opening and to a second air guide port away from the opening.

[0016] The upper air guide grille is arranged horizontally and tilted towards the air guide outlet so that the airflow can be guided to the air guide outlet; the lower air guide grille is arranged vertically.

[0017] The height of the air gap between the upper air guide grille and the silicon photosheet shall not exceed half the distance between the upper air guide grilles.

[0018] The upper support arms on both sides of the air guide outlet directly abut against the surface of the integrated chip to block the airflow from both sides, forcing the airflow to be discharged from the air guide outlet, while also providing a larger support area.

[0019] The protective cover is made of the same material as the PCB board.

[0020] The first guide port is horizontally arranged and connected to the clamp.

[0021] The second flow inlet is arranged horizontally or inclined upwards, and the outlet flows out from the side of the protective cover.

[0022] The second air guide extends upward along the bottom of the clamp to connect with the receiving space, so as to guide the airflow into the receiving space and work together with the airflow from the upper air guide grille on the surface of the silicon wafer.

[0023] The upper left corner of the protective cover is set as an inclined surface, and an upper air guide grille is also formed on the inclined surface.

[0024] This invention provides a carrier system for preventing silicon wafer contamination in a reflow oven. Through the design of double-sided air guide grids in the silicon wafer protective cover, convective airflow can simultaneously heat both sides of the integrated chip. The upper air guide grid adopts an inclined structure, which guides the airflow to be blown obliquely toward the surface of the silicon wafer, so that no particles remain on the surface of the silicon wafer. Even if there are particles, they will be blown away by the oblique airflow. In other words, using the silicon wafer protective cover structure provided by this invention can make the silicon wafer cleaner than before reflow soldering. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the integrated chip described in the background art.

[0026] Figure 2 This is a schematic diagram of a structure in which an integrated chip is carried by a convection carrier.

[0027] Figure 3 This is a three-dimensional structural diagram of a convection vehicle.

[0028] Figure 4 This is a schematic diagram of the three-dimensional structure of the silicon photocell protective cover.

[0029] Figure 5This is a cross-sectional view of the silicon photomask protective cover.

[0030] Figure 6 A side view for protecting silicon photocells.

[0031] Figure 7 A schematic diagram of a structure for holding an integrated chip in place by a protective cover for a silicon photonics wafer.

[0032] Figure 8 A schematic diagram of a structure for holding an integrated chip in place by a protective cover for a silicon photonics wafer.

[0033] Figure 9 This is a schematic diagram of another structure for a silicon photocell protective cover.

[0034] Figure 10 for Figure 9 The image shows a cross-sectional view of a silicon photocell protective cover.

[0035] Figure 11 for Figure 9 Another cross-sectional view of the silicon photomask protective cover shown.

[0036] Figure 12 This is another structural schematic diagram of a silicon photocell protective cover.

[0037] Figure 13 for Figure 12 The cross-sectional view of the silicon photocell protective cover shown.

[0038] Figure 14 This is a schematic diagram of the airflow direction when a silicon photocell protective cover is used.

[0039] In the picture:

[0040] 10. Integrated circuit chip; 11. Through-hole; 12. Silicon photocell;

[0041] 20. Convection carrier; 201. Chip carrier position; 202. Connecting rib; 203. Chip carrier platform; 204. Upper airflow inlet; 205. Lower airflow inlet; 206. Air guide groove; 207. Upper support block; 208. Lower support block; 209. Chip limiting boss;

[0042] 30. Silicon wafer protective cover; 301. Upper support arm; 311. Upper air guide grille; 312. Air guide outlet; 302. Lower support arm; 321. Lower air guide grille; 322. First air guide port; 323. Second air guide port. Detailed Implementation

[0043] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0044] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] Comparative analysis of the implementation examples shows that when using an existing open reflow oven to directly blow airflow onto the surface of the silicon wafer 12, a direct blowing method is used (oblique blowing can cause the chip to be lifted and easily move the molten solder joints). Therefore, the airflow velocity on the surface of the silicon wafer 12 is almost zero. Once particles land on the surface of the silicon wafer 12, they are difficult to blow away, and over time, the particles on the surface of the silicon wafer will only accumulate. This is the root cause of silicon wafer contamination.

[0047] Example 1

[0048] like Figure 2-8As shown, the present invention provides a carrier system for preventing silicon photonics wafer contamination in a reflow oven, used to support an integrated chip 10 with a through-hole in the center, enabling it to be reflow soldered in a convection reflow oven. The system includes a convection carrier 20 and a silicon photonics wafer protective cover 30. The convection carrier 20 has several linearly arranged chip support positions 201, avoiding the position of the silicon photonics wafer 12. The silicon photonics wafer protective cover 30 is U-shaped, clamping the integrated chip 10 through through-holes 11 towards the silicon photonics wafer 12, and housing the silicon photonics wafer 12 within it. Corresponding to the upper surface of the integrated chip 10 with the silicon photonics wafer 12, the upper support arm 301 of the silicon photonics wafer protective cover 30... An inclined upper air guide grille 311 is provided, and a flow channel structure is formed between the upper air guide grilles 311 to guide the airflow and blow it obliquely toward the surface of the silicon photo wafer 12 (the inclination angle is preferably about 45 degrees). An air gap is maintained between the bottom of the upper air guide grille 311 and the silicon photo wafer 12 to allow airflow to pass through. The height of the air gap between the upper air guide grille 311 and the silicon photo wafer 12 should be less than the distance between the upper air guide grilles 311, so that the airflow velocity will increase when the airflow of the upper air guide grille 311 reaches the surface of the silicon photo wafer 12. Corresponding to the side of the integrated chip 10 without the silicon photo wafer 12, the lower support arm 302 of the silicon photo wafer protective cover 30 is provided with a lower air guide grille 321.

[0049] In the technical solution of this invention, an upper air guide grille 311 and a lower air guide grille 321 are simultaneously provided. The upper air guide grille 311 mainly blows air to heat the upper surface of the integrated chip, while the lower air guide grille 321 mainly blows air to heat the lower surface of the integrated chip.

[0050] Preferably, the height of the air gap between the upper air guide grille 311 and the silicon wafer 12 does not exceed half the distance between the upper air guide grilles 311, thereby creating a multiplied airflow velocity on the surface of the silicon wafer 12, which is more conducive to blowing away residues on the surface of the silicon wafer 12. This design is particularly important for the reflow oven environment where the airflow velocity is relatively low, because even if the airflow velocity forms an angle with the surface of the silicon wafer 12, the residual particles on the surface of the silicon wafer 12 are still not blown away due to the low airflow velocity; this technical problem can be solved by adjusting the height of the air gap between the upper air guide grille and the silicon wafer.

[0051] The convection carrier 20 and the silicon photonics protective cover 30 are used together. The integrated chip 10 is placed on the chip carrier position 201 of the convection carrier 20, while the silicon photonics protective cover 30 is clamped on the integrated chip 10 and covers the silicon photonics 12 inside it.

[0052] The upper support arm 301 of the silicon photocell protective cover 30 is provided with an air outlet 312 at its end, which is used to guide the airflow blown toward the silicon photocell 12 through the upper air guide grille 311; the air outlet 312 is also used as the insertion port of the silicon photocell, and its height is higher than that of the silicon photocell 12, so as to avoid the silicon photocell 12 during the insertion of the silicon photocell protective cover 30.

[0053] The upper support arms on both sides of the air guide outlet 312 directly abut against the surface of the integrated chip 10 to block the airflow from both sides, forcing the airflow to be discharged from the air guide outlet 312, while also providing a larger support area.

[0054] The upper air guide grille 311 is sloping or arc-shaped, and the distance between the upper air guide grilles gradually decreases from top to bottom, forming a constricted shape. This is more conducive to further increasing the airflow speed, thereby helping to blow away the residue on the surface of the silicon photo wafer 12.

[0055] The lower air guide grille 321 is perpendicular to the surface of the integrated chip 10, and the lower air guide grille 321 is arranged longitudinally.

[0056] The chip carrier positions 201 on the convection carrier 20 are arranged horizontally and have a concave design, with a longitudinal connecting rib 202 formed between two adjacent chip carrier positions 201. The convection carrier 20 is usually installed on a track or transmission chain, so the convection carrier 20 also needs to be designed with corresponding connection structures at both ends, such as positioning holes, positioning grooves, and slots, to connect and position with the track or transmission chain.

[0057] Each chip carrier position 201 has a horizontally arranged chip carrier platform 203 in the middle. On either side of the chip carrier platform 203 are airflow ports with edges extending beyond the contour of the integrated chip 10: an upper airflow port 204 and a lower airflow port 205. After the integrated chip is installed in the chip carrier position, there are vertical gaps between the edge of the integrated chip and the upper and lower airflow ports to allow convective airflow to pass through. This allows the vertically convecting air, after encountering the obstruction of the integrated chip 10, to continue flowing through the gaps between the integrated chip 10 and the upper and lower airflow ports, thus improving the convection effect.

[0058] At the connection between the chip carrier platform 203 and the connecting ribs on both sides, there is also a recessed air guide groove 206 to allow airflow to pass between the upper and lower air outlets.

[0059] The upper air inlet 204 has upper support blocks 207 protruding inward on both sides; the lower air inlet 205 has lower support blocks 208 protruding inward on both sides.

[0060] The chip carrier stage 203 is provided with a chip limiting protrusion 209. The size of the chip limiting protrusion 209 is smaller than the size of the through hole, and the chip limiting protrusion 209 avoids the silicon photocell protective cover 30. That is, the chip limiting protrusion and the silicon photocell are positioned with a gap so that after the silicon photocell protective cover 30 is installed, the chip limiting protrusion 209 will not interfere with the silicon photocell protective cover.

[0061] This invention provides a carrier system for preventing silicon wafer contamination in a reflow oven. Through the design of double-sided air guide grids in the silicon wafer protective cover, convective airflow can simultaneously heat both sides of the integrated chip. The upper air guide grid adopts an inclined structure, which guides the airflow to be blown obliquely toward the surface of the silicon wafer, so that no particles remain on the surface of the silicon wafer. Even if there are particles, they will be blown away by the oblique airflow. In other words, using the silicon wafer protective cover structure provided by this invention can make the silicon wafer cleaner than before reflow soldering.

[0062] Example 2

[0063] like Figure 9-14 As shown, the present invention provides a silicon photocell protective cover that ensures convection and cleans the silicon photocell. The protective cover is U-shaped, and when placed horizontally, a horizontal clamp is formed in the middle, with the clamp facing to the right as shown in the figure. The protective cover provided in this embodiment includes an upper support arm 301 and a lower support arm 302. The upper support arm 301 is provided with an upper air guide grille 311 arranged from top to bottom, and the lower support arm 302 is provided with a lower air guide grille 321 arranged vertically. The upper support arm 301 has an air guide outlet 312 at its opening, and the upper air guide grille 311 inside the air guide outlet 312 forms a concave receiving space to accommodate the silicon photocell 12. The lower air guide grille 321 of the lower support arm 302 is connected to a first air guide port 322 near the opening and to a second air guide port 323 away from the opening.

[0064] The upper air guide grille is arranged horizontally 311 and tilted towards the air guide outlet 312 so that the airflow can be guided to the air guide outlet 312; the lower air guide grille 321 is arranged vertically; in this embodiment, the horizontal and vertical directions are relative to the clamping and installation direction of the protective cover, that is, if it is the same as the clamping and installation direction of the protective cover, it is the vertical direction, and if it is perpendicular to the clamping and installation direction of the protective cover, it is the horizontal direction.

[0065] The height of the air gap between the upper air guide grille 311 and the silicon photo wafer 12 shall not exceed half the distance between the upper air guide grilles (so that those skilled in the art can observe it clearly). Figure 14 The air gap has been enlarged; please refer to the instruction manual for details.

[0066] The upper support arms on both sides of the air guide outlet 312 directly abut against the surface of the integrated chip 10 to block the airflow from both sides, forcing the airflow to be discharged from the air guide outlet, while also providing a larger support area.

[0067] The protective cover is made of the same material as the PCB board.

[0068] The first guide port 322 is horizontally arranged and connected to the clamp.

[0069] The second guide port 323 is horizontally arranged (see reference). Figure 10 ) or tilted upwards (reference) Figure 11 The arrangement is such that the outlet flows out from the side of the protective cover.

[0070] refer to Figure 13 The optimal choice is to design the second air guide port 323 to extend upwards along the bottom of the clamp to communicate with the receiving space, so as to guide the airflow into the receiving space and work together with the airflow from the upper air guide grille on the surface of the silicon wafer. The advantage of this design is that even when blowing towards the back of the integrated chip 10 without the silicon wafer 12, the airflow can still be guided to the side with the silicon wafer 12 through the second air guide port 323, thus utilizing the airflow from the back to treat the silicon wafer surface. In practical applications, the design of the second air guide port 323 perfectly guides the airflow from both sides of the integrated chip 10 to the surface of the silicon wafer 12, thereby achieving efficient purging of the silicon wafer surface and making its treatment effect more effective. This structure is best suited for reflow oven applications with low airflow velocities.

[0071] The upper left corner of the protective cover is designed with an inclined surface, and an upper air guide grille is also machined onto this inclined surface. This significantly shortens the airflow time at the upper right corner, reduces the obstruction effect of the flow channel on the airflow, and thus improves the treatment effect on the silicon wafer surface at the upper left corner. The airflow velocity on the silicon wafer surface is higher closer to the air guide outlet, and the velocity is lowest near the bottom of the clamp (i.e., the silicon wafer surface corresponding to the bottom of the upper air guide grille in the upper right corner). Therefore, the inclined surface design of the protective cover can improve the purging treatment of the blind area (low-speed area) on the silicon wafer surface. This design further... Figure 13 The combination of the second guide port 323 shown can significantly increase the purging effect on the left side surface of the silicon wafer.

[0072] The silicon wafer protective cover provided in this embodiment makes full use of the convective airflow on the upper and lower surfaces, guiding the convective airflow on both sides to the silicon wafer surface, thereby solving the problem of silicon wafer surface contamination caused by low-speed, vertical airflow in the reflow oven.

[0073] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A carrier system for preventing silicon wafer contamination in a reflow oven, used to support integrated chips with through-holes in the center, enabling them to be reflow soldered in a convection reflow oven, characterized in that, The device includes a convection carrier and a silicon photonics wafer protective cover. The convection carrier has several linearly arranged chip carrier positions that avoid the position of the silicon photonics wafer. The silicon photonics wafer protective cover is U-shaped and clamps the integrated chip through a through-hole towards the silicon photonics wafer, and houses the silicon photonics wafer therein. Corresponding to the side of the integrated chip with silicon photodiode, the upper arm of the silicon photodiode protective cover is provided with an inclined upper air guide grille, and an air gap is maintained between the bottom of the upper air guide grille and the silicon photodiode to allow airflow to pass through; corresponding to the side of the integrated chip without silicon photodiode, the lower arm of the silicon photodiode protective cover is provided with a lower air guide grille.

2. The vehicle system according to claim 1, characterized in that, The upper support arm of the silicon wafer protective cover is provided with an air outlet at its end, which is used to guide the airflow that is blown toward the silicon wafer through the upper air guide grille; the air outlet also serves as the insertion port for the silicon wafer, and its height is higher than that of the silicon wafer, so as to avoid the silicon wafer during the insertion of the silicon wafer protective cover.

3. The vehicle system according to claim 2, characterized in that, The upper support arms on both sides of the air outlet directly abut against the surface of the integrated chip to block the airflow from both sides, forcing the airflow to be discharged from the air outlet, while also providing a larger support area. The height of the air gap between the upper air guide grille and the silicon photosheet shall not exceed half the distance between the upper air guide grilles.

4. The vehicle system according to claim 2, characterized in that, The upper air guide grille is sloping or curved, and the distance between the upper air guide grilles gradually decreases from top to bottom, forming a constricted shape.

5. The vehicle system according to claim 2, characterized in that, The lower air guide grille is perpendicular to the surface of the integrated chip, and the direction of the lower air guide grille is arranged longitudinally.

6. The vehicle system according to claim 1, characterized in that, The chip carrier positions on the convection carrier are arranged horizontally and have a concave design, with longitudinal connecting ribs formed between adjacent chip carrier positions.

7. The vehicle system according to claim 6, characterized in that, Each chip carrier position has a horizontally arranged chip carrier platform in the middle, and on both sides of the chip carrier platform are airflow ports with edges extending beyond the outline of the integrated chip: an upper airflow port and a lower airflow port; the integrated chip is installed after the chip carrier position, and there is a vertical gap between the edge of the integrated chip and the upper and lower airflow ports to allow convective airflow to pass through.

8. The vehicle system according to claim 7, characterized in that, The connection between the chip carrier and the connecting ribs on both sides is also provided with a recessed air guide groove to allow airflow between the upper and lower air outlets.

9. The vehicle system according to claim 7, characterized in that, The upper air inlet has inwardly protruding upper support blocks on both sides; the lower air inlet has inwardly protruding lower support blocks on both sides.

10. The vehicle system according to claim 7, characterized in that, The chip carrier platform is provided with a chip limiting protrusion. The size of the chip limiting protrusion is smaller than the size of the through hole, and the chip limiting protrusion avoids the silicon photodiode protective cover. That is, the chip limiting protrusion and the silicon photodiode are positioned with a gap to allow the chip limiting protrusion to not interfere with the silicon photodiode protective cover after it is installed.

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