Improved method to ensure high quality MEMS capping

Abstract

The present invention relates to an improved method for ensuring high-quality MEMS capping, comprising the following steps: a pressing block correction process: using a pressing block to press a substrate, and then baking the pressing block and substrate in a high-temperature environment; laser marking: using a high-precision laser printer to print laser marks around each product unit on the substrate; automatic glue application and automatic capping: using a glue application machine to apply glue to the edges of the product unit, and using an automatic capping machine to apply the cap to the glue; inspection and correction: using automatic optical inspection equipment to inspect semi-finished products; laser printing: laser printing on the product unit as required for easy identification; and cutting: using a cutting machine to cut the product unit into individual finished products. This method ensures that all products after capping are qualified and solves the problem of blade breakage during the cutting process.

Description

Technical Field

[0001] The present invention relates to a MEMS capping method, and in particular to an improved method for ensuring high-quality MEMS capping. Background Art

[0002] In the MEMS packaging process, metal capping is a common process due to the special space required for movement of MEMS micromechanics. MEMS packaging typically uses multi-chip assembly, which combines the MEMS chip and the signal conversion ASIC chip. This characteristic determines that MEMS packaging adopts a wiring substrate packaging format. Because the resin substrate integrates the multi-chip package, the multiple steps of high-temperature curing of silver paste and plastic resin curing are used, so the substrate often undergoes significant deformation during the packaging process.

[0003] Adding a metal cover is generally a back-end process after the MEMS chip is mounted and bonded. The typical system-level packaging process is as follows: primary mounting, silver paste curing and baking, plasma cleaning, primary bonding, optical inspection, plasma cleaning, plastic sealing, post-curing, secondary mounting, silver paste curing and baking, warp correction baking, secondary bonding, optical inspection, dehumidification baking, UV glue application, UV glue curing, automatic glue painting and automatic cover application, cover application and baking, laser printing, product cutting, optical inspection, automatic loading and shipment inspection. Before cover application, the substrate has undergone multiple high-temperature curing procedures and has undergone significant deformation. Although automatic detection and positioning functions are used in the capping process, when the thickness of the substrate and the resin reaches a relatively thick level (for example, more than 1 mm), the pressure plate correction of the equipment itself in the capping process cannot achieve true leveling, and the vacuum cannot be adsorbed. The cap often shifts, causing the cutting knife to break in the next cutting process and resulting in product defects. Summary of the Invention

[0004] In order to overcome the above-mentioned defects, the present invention provides an improved method for ensuring high-quality MEMS capping, which adds a block correction process, a laser marking process and an automatic detection process, thereby ensuring that all products after capping are qualified and solving the problem of knife breakage during the cutting process.

[0005] The technical solution adopted by the present invention to solve its technical problems is:

[0006] An improved method for ensuring high-quality MEMS capping includes the following steps:

[0007] Step 1: Pressing block correction process: Use a pressing block to press the substrate, and place the pressing block and the substrate in a high temperature environment for baking. The baking conditions are: baking temperature of 160-180℃, baking time of 15-30min, and the substrate includes several product units;

[0008] Step 2: Laser marking: Use a high-precision laser printer to print laser marks around each product unit on the substrate;

[0009] Step 3: Automatic glue application and automatic capping: Use a glue application machine to apply glue on the edge of the product unit, and use an automatic capping machine to stick the cap on the glue. The glue is cured at high temperature to combine the cap with the substrate to obtain a semi-finished product. The cap is located inside the laser marking.

[0010] Step 4: Inspection and Correction: Automated optical inspection equipment is used to inspect semi-finished products and identify product units with unqualified caps. The caps are then manually corrected to ensure 100% compliance.

[0011] Step 5: Laser printing: Laser print on the product unit as required for easy identification;

[0012] Step 6: Cutting: Use a cutting machine to cut the product unit into individual finished products.

[0013] Preferably, in step one, the pressing blocks include large pressing blocks and small pressing blocks made of steel, and a plurality of small pressing blocks and a plurality of substrates are stacked together at intervals to form a substrate stack. A large pressing block is pressed on the top substrate of each substrate stack, and the weight of each large pressing block is 3-4 kg, and the weight of each small pressing block is 0.5-1.5 kg.

[0014] Preferably, in step 1, the flatness of the pressing block is ≤0.1 mm, the weight of each large pressing block is 3±0.2 kg, and the weight of each small pressing block is 1±0.2 kg. During baking, the entire substrate stack is placed in a high temperature environment, and the baking conditions are: baking temperature is 175° C., and baking time is 20 min.

[0015] Preferably, in step 2, the laser mark is printed within a tolerance range of the capping position, and the laser mark is distributed all around the product unit or is arranged at the four corners of the product unit.

[0016] Preferably, in step four, the detection standard of the center point deviation value of the product unit is set to ±60μm in advance in the automatic optical inspection equipment, and then the automatic optical inspection system is used to inspect the cover of the product unit according to the detection standard, and the detection results are displayed through images, and unqualified products are marked in the image.

[0017] The beneficial effects of the present invention are:

[0018] 1) The present invention adds a flattening correction process before capping, which reduces the warping of the substrate from more than 1.5mm before correction to less than 0.5mm after correction, resulting in a relatively flat substrate and improving the accuracy of the capping position of the substrate. In other words, the capping operation is more convenient on a flat substrate;

[0019] 2) The present invention utilizes a laser printer from the outset to accurately determine the capping range during the capping process, eliminating the need for complex and time-consuming microscopic measurements of each batch of products to determine the capping range. Furthermore, after capping, defective products can be quickly identified manually using an ordinary microscope based on the laser marking, eliminating the need for repeated use of a microscopic measurement to determine capping accuracy.

[0020] 3) The present invention introduces a universal fully automatic optical inspection device to quickly inspect each product unit after capping. Using a preset offset value, all products can be inspected. Defective products can be manually corrected to ensure that each capping unit is within the set range, thus achieving 100% product quality.

[0021] 4) The laser printer and fully automatic optical inspection system used in the present invention are both traditional equipment, which only requires the equipment supplier to develop specific usage functions. Therefore, the equipment cost is almost not increased and the scope of use of the equipment is expanded. The equipment used in the present invention is simple and easy to operate. It completely solves the problem of broken knife in cutting products caused by cover deviation without increasing costs, and has very strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a simplified diagram of a substrate stack in the present invention;

[0023] Figure 2 is a simplified diagram of the substrate in the present invention;

[0024] Figure 3 A simplified diagram of a product unit in the present invention;

[0025] Figure 4 This is a warping diagram of the substrate before the pressing block is corrected in the present invention;

[0026] Figure 5 This is a picture of the substrate warping after the pressing block in the present invention has been corrected;

[0027] In the figure: 10-substrate, 11-product unit, 12-laser mark, 21-large pressing block, 22-small pressing block. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0030] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0031] An improved method for ensuring high-quality MEMS capping includes the following steps:

[0032] Step 1: Briquetting and correction process: Figure 1 As shown, the substrate 10 is pressed by a pressing block, and the pressing block and the substrate are placed in a high temperature environment for baking. The baking conditions are: baking temperature is 160-180°C, and baking time is 15-30 minutes. The substrate 10 includes several product units 11, such as Figure 2As shown; the present invention adds a substrate correction process before the cover is attached, by pressing the substrate with a pressing block and baking the substrate at a high temperature, the high temperature reaches the temperature for plastic sealing and curing, thereby improving the correction effect, which can greatly reduce the warping of the substrate, so that the warping of the substrate 10 is greater than 1.5mm (as shown in FIG. Figure 4 as shown) down to 0.5mm after correction (as shown) Figure 5 As shown), a flat substrate is provided for the subsequent capping process.

[0033] Step 2: Laser marking: Use a high-precision laser printer to print laser markings 12 around each product unit 11 on the substrate 10; Figure 3 As shown, in order to more easily identify the offset of the cover, a high-precision laser printer is used to print a laser mark in advance within the tolerance range of the product unit cover position. The position offset of each product unit can be controlled within the range of 50μm. Since the next process is to apply the glue and then apply the cover, according to the process requirements, the edge glue will be squeezed out. Therefore, optionally, the laser mark 12 is printed on the four corners of the product unit. The subsequent cover process only needs to stick the cover within the laser mark 12. If the cover is offset, it is also easy to identify. The traditional laser printer only marks the specifications and models of the device on the substrate. The present invention uses a laser printer to print a laser mark on the product, which can guide the debugging and placement operation of the offset placement machine, and is conducive to the preliminary and rapid identification of defective products after the cover is applied, and has strong operability.

[0034] Step 3: Automatic glue application and automatic lid application: Use a glue application machine to apply glue on the edge of the product unit, use an automatic lid application machine to apply the lid on the glue, and cure the glue at high temperature to combine the lid with the substrate 10 to obtain a semi-finished product. The lid is located inside the laser mark 12. After the lid is applied, a preliminary inspection is performed using an ordinary microscope to quickly identify the lid that is not within the laser mark and correct it. Due to the presence of the laser mark, the deflected lid is clearly visible, so it can be seen using an ordinary microscope, without the need for traditional measuring microscopes to perform complex measurements, which is time-consuming and labor-intensive.

[0035] Step 4: Inspection and Correction: Automated optical inspection equipment is used to inspect semi-finished products and identify any unqualified caps. Manual corrections are then performed to ensure 100% compliance. Traditional processes use manual inspection for cap offset, which requires significant manpower and time, and cannot guarantee 100% accuracy. This invention introduces fully automated optical inspection equipment to detect cap offset. Using preset offset values, the entire product can be inspected, and any unqualified units can be manually corrected, ensuring 100% product compliance. Traditional optical inspection equipment for packaging is generally used to detect functional issues such as desoldering of bond balls, product contamination, and regional chip scratches. This invention overcomes the limitations of automated optical inspection equipment.

[0036] Step 5: Laser printing: Laser print on the product unit as required for easy identification;

[0037] Step 6: Cutting: A cutting machine is used to cut the product unit into individual finished products. This invention incorporates a high-temperature flattening process before capping, reducing the warpage of the substrate from approximately 1.5mm to approximately 0.5mm. A laser printer is then used to precisely mark the perimeter of the product unit. After capping, laser marking is used for a quick preliminary inspection to correct any cap deviations. Finally, a fully automated optical inspection system is introduced to fully test cap deviation accuracy, ensuring that the deviation is within 260-380µm from the center point, ensuring a 100% pass rate for the capping process.

[0038] Preferably, in step 1, the pressing blocks include a large pressing block 21 and a small pressing block 22 made of steel. Several small pressing blocks 22 are stacked together with several substrates 10 at intervals to form a substrate stack. A large pressing block 21 is pressed on the top substrate of each substrate stack. The weight of each large pressing block 21 is 3-4 kg, and the weight of each small pressing block 22 is 0.5-1.5 kg. After many experiments, it was found that Figure 1 As shown, small pressing blocks are arranged at intervals with the substrate, and a large pressing block is pressed on the top substrate, wherein the weight of the small pressing block is about 1 kg, and the weight of the large pressing block is about 3.5 kg. Under such conditions, the flatness of the substrate obtained is high. If the weight of the large pressing block and the small pressing block is too light, the flattening effect is not good; if the weight of the large pressing block and the small pressing block is too heavy, the flattening effect will not be further improved, and the substrate will be easily damaged.

[0039] In step one, the flatness of the pressing blocks is ≤0.1mm, the weight of each large pressing block 21 is 3±0.2kg, and the weight of each small pressing block 22 is 1±0.2kg. During baking, the entire substrate stack is placed in a high-temperature environment under the following baking conditions: baking temperature is 175°C and baking time is 20 minutes. During the correction process, the flatness of the pressing blocks themselves is also critical. If the flatness of the pressing blocks is greater than 0.1mm, the contact area between the pressing blocks and the substrate is small, and the final correction effect of the substrate is poor. The baking temperature is maintained at the temperature of the previous plastic sealing process, which not only ensures the plastic sealing effect of the substrate but also improves the correction effect.

[0040] In step 2, the laser mark 12 is printed within the tolerance range of the cover attachment position. The laser mark 12 is distributed all around the product unit 11 or is arranged at the four corners of the product unit 11. That is, as long as the cover is attached within the range of the laser mark 12, the cover can meet the preset tolerance range, ensuring that the obtained product is a qualified product. Figure 3 As shown, just print the laser mark on the four corners of the product.

[0041] In step 4, the automated optical inspection system (AOI) pre-sets a standard of ±60μm deviation for the center point of product unit 11. The AOI system then inspects the lid of product unit 11 according to this standard, displays the inspection results in an image, and identifies defective products in the image. The inspection results are displayed on a monitor, with all qualified products displayed in green and defective products in red. This allows operators to easily identify and correct defective products, achieving a 100% product pass rate.

[0042] It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. An improved method for ensuring high-quality MEMS capping, characterized by: The following steps are involved: Step 1: Pressing block correction process: using a pressing block to press the substrate (10), and placing the pressing block and the substrate in a high temperature environment for baking, the baking conditions are: baking temperature of 160-180° C., baking time of 15-30 minutes, and the substrate (10) includes a plurality of product units (11); Step 2: Laser marking: using a high-precision laser printer to print laser markings (12) around each product unit (11) on the substrate (10); Step 3: Automatic glue application and automatic cap application: Glue is applied to the edge of the product unit using a glue application machine, the cap is attached to the glue by an automatic cap application machine, and the glue is cured at high temperature to combine the cap with the substrate (10) to obtain a semi-finished product, wherein the cap is located inside the laser marker (12); Step 4: Inspection and Correction: Automated optical inspection equipment is used to inspect semi-finished products and identify product units with unqualified caps. The caps are then manually corrected to ensure 100% compliance. Step 5: Laser printing: Laser print on the product unit as required for easy identification; Step 6: Cutting: Use a cutting machine to cut the product unit into individual finished products.

2. The improved method for ensuring high-quality MEMS capping according to claim 1, characterized in that: In step 1, the pressing blocks include a large pressing block (21) and a small pressing block (22) made of steel. A plurality of small pressing blocks (22) and a plurality of substrates (10) are stacked together at intervals to form a substrate stack. A large pressing block (21) is pressed on the top substrate of each substrate stack. The weight of each large pressing block (21) is 3-4 kg, and the weight of each small pressing block (22) is 0.5-1.5 kg.

3. The improved method for ensuring high-quality MEMS capping according to claim 2, characterized in that: In step 1, the flatness of the pressing block is ≤0.1 mm, the weight of each large pressing block (21) is 3±0.2 kg, and the weight of each small pressing block (22) is 1±0.2 kg. During baking, the entire substrate stack is placed in a high-temperature environment, and the baking conditions are: baking temperature is 175° C., and baking time is 20 minutes.

4. The improved method for ensuring high-quality MEMS capping according to claim 1, characterized in that: In step 2, the laser mark (12) is printed within the tolerance range of the capping position, and the laser mark (12) is distributed all around the product unit (11) or the laser mark is arranged at the four corner ends of the product unit (11).

5. The improved method for ensuring high-quality MEMS capping according to claim 1, characterized in that: In step 4, a detection standard of a center point deviation value of ±60 μm of the product unit (11) is set in advance in the automatic optical inspection equipment, and then the automatic optical inspection system is used to inspect the cover of the product unit (11) according to the detection standard, and the detection result is displayed through an image, and unqualified products are marked in the image.

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