Preparation method of metallographic specimen of CSP (Chip Scale Package) device
By employing a specially designed elastic thin-film clamp and double potting technology, the problems of internal structural damage and unclear grinding profiles in the preparation of metallographic samples for CSP devices were solved, achieving high-quality metallographic sample preparation and ensuring observation results.
Patent Information
- Application Number
- CN202511887391.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-15
- Publication Date
- 2026-02-03
AI Technical Summary
Existing technologies make it difficult to avoid damage to the internal structure when preparing metallographic specimens of CSP devices, and it is also difficult to obtain clear grinding profiles, especially for small-sized complex flip-chip structures and CSP devices with cavities.
Using a specially designed elastic thin sheet clamp and double potting technology, the CSP device is fixed by the elastic thin sheet clamp. The first and second inserts are used in combination for segmented grinding and adjustment. Combined with the grinding and polishing of the double-disc semi-automatic metallographic grinding and polishing machine, the stability of the device and the grinding and polishing effect are ensured.
This effectively avoids damage to the internal structure, enables the acquisition of a clear interface structure, improves the observation effect of metallographic samples, and ensures the integrity of the device and the accuracy of observation.
Smart Images
Figure CN121453486A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of CSP device manufacturing, in particular to a CSP device metallographic sample preparation method. BACKGROUND
[0002] Metallographic analysis is an important means of testing and analyzing materials, aiming to reveal the true structure of the material. In order to conduct metallographic analysis, a sample that can be used for microscopic observation and testing must be prepared - a metallographic sample. In metallographic analysis, the selection and preparation of representative samples are very important. Generally, the preparation of a metallographic sample includes sampling, grinding, polishing, etching and other steps, and the sample prepared must have a smooth grinding surface, clear structure, and no obvious scratches, watermarks, impurities and other defects in the field of view. In addition, during the preparation of the sample, improper operation may damage or deform the sample, affecting the testing results. Therefore, the selection of a reasonable preparation method is particularly important.
[0003] CSP (Chip Scale Package) refers to chip size packaging or chip level packaging. CSP is the latest generation of chip packaging technology based on flip-chip technology, which mainly reflects the total volume of the device after packaging being approximately equal to or not greater than 20% of the chip volume, with compact structure, small solder joint size, and internal cavity. At present, the diameter of the mainstream CSP flip-chip solder joint is as small as 50-100 μm (or even smaller), and product reliability analysis often requires observation of solder balls and pads and other structures. How to avoid damage to sensitive structures during sample preparation and how to prepare clear and accurate interface structures have become a difficult problem for the industry. SUMMARY
[0004] In view of the problems that the traditional metallographic sample preparation method cannot complete the preparation of high-quality small-size, complex flip-chip structure and CSP device with cavity, and is prone to damage to the internal structure of the device during sample preparation, grinding tilt and other problems, the present application provides a CSP device metallographic sample preparation method, which specifically includes the following steps:
[0005] The left and right ends of the CSP device are clamped by two elastic sheet clamps, so that they are fixed in the first inlay mold, and the first inlay material is filled in the first inlay mold. One end of the elastic sheet clamp gradually narrows towards the other end, and the wider end of the elastic sheet clamp is flush with one side of the CSP device.
[0006] The first inlay mold filled with the inlay material is fixed in the second inlay mold, and the grinding starts from the wider end of the elastic sheet clamp until the device housing end wall is removed to expose the chip of the CSP device.
[0007] Injecting the second inlay material into the shell of the CSP device, so that the second inlay material completely wraps the chip and the flip-chip solder joint of the CSP device;
[0008] Continuing to grind the CSP device, and judging whether the exposed lengths and angles of the two elastic sheet clamps are consistent after grinding, and if not, grinding in the direction to make them consistent.
[0009] Further, the two right-angled triangular sheets are connected at one of their acute corners, and the side between the acute corner and the right angle of the triangle serves as the bottom of the elastic sheet clamp; the clamping part is arranged between the other acute sides of the two triangular sheets, and matches the CSP device to clamp and fix the CSP device.
[0010] Preferably, the clamping part includes two left and right parts, each part being composed of two sheets in an L shape, one end of one sheet of each part being connected to the right-angled side of the two right-angled triangular sheets other than the bottom, and the other two sheets being used to clamp the CSP device.
[0011] Preferably, the clamping part is an arbitrary-shaped metallographic section clamp, which is connected to the right-angled side of the triangular sheet other than the bottom.
[0012] Further, during grinding, the bottom of the elastic sheet clamp is flush with one side of the CSP device, and grinding starts from the four bottoms of the elastic sheet clamp.
[0013] Further, the material of the elastic sheet clamp is PET plastic, epoxy resin or stainless steel.
[0014] Further, the first inlay material is denture powder and water.
[0015] Further, the second inlay material is a material that is hard, has good fluidity, expands and has small polymerization shrinkage when solidified.
[0016] Further, the second inlay material is a combination of self-curing or hot-curing denture powder and a curing liquid.
[0017] Further, a double-disc semi-automatic metallographic grinding and polishing machine loaded with sandpaper is used for grinding, and when the chip is completely exposed and the two ends of the elastic sheet clamp are flush, a double-disc semi-automatic metallographic grinding and polishing machine loaded with polishing cloth is used for polishing to obtain an ideal metallographic interface.
[0018] Further, the rotation speed of the double-disc semi-automatic metallographic grinding and polishing machine is set to 600-1200 r / min, and 320-mesh, 800-mesh and 1200-mesh water sandpaper are used in combination from coarse to fine.
[0019] Further, when polishing, the rotation speed of the double-disc semi-automatic metallographic polishing and grinding machine is set to 800-1000 r / min, and short velvet cloth is used to polish together with 2.5 mu m and W0.5 mu m particle size diamond spray polishing liquid.
[0020] Further, the CSP device is a cavity sealing structure, the internal chip is connected with the substrate by means of flip or bonding, and then the chip is covered on the substrate by the shell.
[0021] Compared with the prior art, the present application has the following advantages:
[0022] 1. The present application adopts double-time encapsulation sample preparation, which avoids damage to the internal structure;
[0023] 2. The present application adopts a specially-made elastic sheet clamp, which can effectively fix the device for inlaying sample preparation and detect and correct the tilt misalignment in the polishing of the device, and it is easier to obtain an ideal interface;
[0024] 3. The design and use of the elastic sheet clamp of the present application facilitate grinding operation and can segmentally grind or dynamically adjust the grinding angle. BRIEF DESCRIPTION OF DRAWINGS
[0025] Figure 1 It is a CSP device structure schematic diagram;
[0026] Figure 2 It is a schematic diagram of the elastic sheet clamp structure of the present application;
[0027] Figure 3 It is a schematic diagram of the assembly of the elastic sheet clamp and the CSP device of the present application;
[0028] Figure 4 It is a schematic diagram of the assembly of the first inlaying mold of the present application;
[0029] Figure 5 It is a schematic diagram of the structure of the second inlaying mold of the present application;
[0030] Figure 6 It is a schematic diagram of the baffle of the second inlaying mold of the present application;
[0031] Figure 7 It is a schematic diagram of the assembly of the second inlaying mold. DETAILED DESCRIPTION
[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.
[0033] The application provides a CSP device metallographic sample preparation method, and specifically comprises the following steps.
[0034] The left and right ends of the CSP device are clamped by two elastic sheet clamps, so that the CSP device is fixed in the first inlay mold, the first inlay material is filled into the first inlay mold, one end of the elastic sheet clamp gradually narrows to the other end, and the wider end of the elastic sheet clamp is flush with one side of the CSP device;
[0035] The first inlay mold filled with the inlay resin is fixed in the second inlay mold, and the grinding starts from the wider end of the elastic sheet clamp until the end wall of the device shell is removed to expose the chip of the CSP device;
[0036] The second inlay material is injected into the shell of the CSP device, so that the second inlay material completely wraps the chip and the flip-chip of the CSP device;
[0037] The grinding of the CSP device is continued, and whether the exposed length and angle of the two elastic sheet clamps after grinding are consistent is judged, and if not, the grinding is carried out in the direction of making them consistent.
[0038] As shown in Figure 1 , the CSP device is a flip-chip structure, that is, the chip 2 is inverted and mounted on the substrate 4 through the solder ball 3, and then the shell 1 is packaged; the solder ball can be a gold ball, a copper column and a tin-containing solder bump, and the height is 30-200 μm; the substrate and the shell are made of any material, such as resin, metal, ceramic, etc. The chip is made of Si, SiC, LiNbO3, GaAs, etc. The chip and the shell, the substrate are a cavity structure, and no other material is filled.
[0039] The elastic sheet clamp used in the application is a triangular symmetric stable structure, comprising two right-angled triangular sheets and a clamping part, wherein one acute corner of the two right-angled triangular sheets is connected together, and the side between the acute corner and the right angle of the triangle serves as the bottom of the elastic sheet clamp; the clamping part is arranged between the other acute sides of the two triangular sheets, and the clamping part is matched with the CSP device and used for clamping and fixing the CSP device, Figure 2 (a) is a side view of the elastic sheet clamp, Figure 2 (b) is a top view of the elastic sheet clamp, the size of which is set according to the size of the device, so that the end surface parallel region can clamp and fix the device, and the device can be kept fixed and upright during the filling and curing of the inlay material. In the embodiment, the clamping part comprises left and right two parts, each part is composed of two sheets to form an L-shaped structure, the right end of the elastic sheet clamp is parallel, that is, one sheet of the L-shaped structure is used for clamping and fixing the device, and the spacing between the two sheets used for clamping of the two L-shaped sheets is slightly smaller than the thickness of the device, so that the clamping state is maintained, and the shape can be made according to the shape of the device.
[0040] As Figure 3 , in use, two elastic sheets are used to clamp the two ends of the CSP device respectively, so that the device is stable during inlaying. In addition, during subsequent sample grinding and polishing, it can play a role in leveling the ruler. During normal grinding, the elastic sheet clamp will be removed at the same height as the inlay and the device is ground, and when the device is ground skewed, the length and angle of the left and right triangular clamps will also change, causing asymmetric conditions to occur, prompting the operator to make real-time adjustments to level and ensure that the ideal cross-section is obtained.
[0041] The material of the elastic sheet clamp is not limited and can be PET plastic, epoxy resin, stainless steel, etc. and should not react with the CSP device inlay.
[0042] In addition, the present application can not be limited to the part for fixing the CSP device, and any existing metallographic section clamp can be selected as the clamping part, which is arranged between two right-angled triangular sheets and fixedly connected with the right-angled triangular sheets, so that the right-angled edges of the right-angled triangular sheets are flush with the bottom of the clamp and the downward end of the clamped CSP device, facilitating adjustment of the grinding direction and whether further grinding is needed during metallographic sample preparation.
[0043] As an optional embodiment, Figure 4 , the elastic sheet clamp clamps the left and right ends of the CSP device respectively and is placed at the bottom of the first inlay mold. The first inlay mold should be as small as possible on the basis of being able to accommodate the CSP device clamped by the elastic sheet clamp, saving the encapsulation inlay material. To prevent leakage at the bottom of the mold during inlay pouring, the mold can be fixed with the triangular clamp and the device on a horizontal glass plate or steel plate with double-sided tape, and then poured in sections combined with the above method.
[0044] Preferably, the first inlay mold should be a cylindrical thin-walled hard alloy or plastic that is not easy to deform, and whether it is removed or not does not affect the sample preparation result.
[0045] Preferably, the first inlay material can be composed of a metallographic curing agent and a metallographic glue powder, and the first inlay material should be poured in small doses in sections (multiple times) to fully wet and fill the pores between the chip and the triangular spring clamp, avoiding air bubbles that affect subsequent grinding and polishing.
[0046] As Figure 5 , the second inlay mold is composed of two baffles and two fastening screws, and the baffles are provided with a strip-shaped sliding groove. The size of the sliding groove should be larger than that of the screw and smaller than that of the end cap, as shown in Figure 6 . The assembly of the first inlay mold and the second inlay mold is as shown in Figure 7Put the first inlay mold into the second inlay mold, and fasten the screw according to the size of the device, and the baffle and the screw should be in contact with the first inlay mold and remain clamped. The bottom of the second inlay mold should be above the expected device grinding section, that is, the part to be removed by grinding at the lower end of the first inlay mold should be exposed. When the grinding removal amount is small, the method of segmented clamping and grinding removal can also be used, that is, under the premise of horizontal clamping, the small amount of exposed first inlay mold is completely removed, and then the clamp is loosened and clamped again, which avoids the occurrence of grinding tilt from the grinding method.
[0047] When assembling, the contact between the first inlay mold and the clamp baffle should be a line, and the point contact with the screw, at this time, the left and right elastic sheet clamps used for clamping should be parallel or perpendicular to the baffle, and when the grinding and polishing are tilted, the adjustment function can be more directly realized by relying on the clamp.
[0048] Further, during the grinding process, the flip-chip structure is relatively complex and relatively fragile. Therefore, in order to avoid damage to the chip and the solder structure caused by sandpaper or polishing cloth during grinding and polishing, the cavity is filled when the device shell end wall is ground to expose the chip, and the second metallographic inlay material is used to wrap the chip and the flip-chip solder joint. When filling, a small size rubber tube should be used for slow dripping, and air in the cavity should be fully discharged to make the inlay liquid fully wrap the solder joint and the chip.
[0049] The second metallographic inlay material should be a material with hard and small expansion and polymerization shrinkage after solidification, so as to avoid damage to the flip-chip structure during solidification. The material selection is not limited, and the recommended preferred is: self-coagulation / thermal coagulation denture powder + denture water combination, and the powder / liquid ratio is recommended to be 2:1. The ratio of denture powder and denture water can be adjusted according to the filling size of the exposed cavity of the device to change the concentration of the filling colloid, so as to realize complete filling and wrapping. The solidification conditions of the glue after pouring are set according to the selected material, and sufficient solidification should be ensured.
[0050] The parameters of the grinding and polishing process itself should be set according to the grinding machine and the properties of the CSP device itself to realize non-damage and fast and efficient grinding and polishing. The recommended parameters are as follows:
[0051] Grinding and polishing machine: double-disc semi-automatic metallographic grinding and polishing machine, one disc loaded with sandpaper for grinding, and the other disc loaded with polishing cloth for metallographic polishing to obtain an ideal metallographic interface; recommended 320 mesh, 800 mesh and 1200 mesh water sandpaper is used from coarse to fine, and the grinding and polishing machine speed is 600~1200r / min, which can balance the efficiency while realizing higher grinding quality; the recommended polishing disc speed is 800~1000r / min, the short pile polishing cloth is used, and 2.5μm and W0.5μm particle size diamond spray polishing liquid is used for polishing to remove scratches and micro-deformation layer generated by the device during grinding interface, so as to obtain the best metallographic observation effect.
[0052] The polishing process is dynamically rinsed with deionized water, and the polishing interface is observed under a stereomicroscope with magnification of not less than 50X, and then the polishing surface is briefly rinsed with anhydrous ethanol to completely remove the water stains on the metallographic interface, and after drying, the subsequent observation and detection process can be performed.
[0053] In the description of the present application, it should be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "outer", "front", "central", "both ends" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.
[0054] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "setting", "connecting", "fixing", "rotating" and the like should be understood broadly, for example, can be fixedly connected, can also be detachably connected, or can be integrated; can be mechanically connected, can also be electrically connected; can be directly connected, can also be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited, the above-mentioned terms in the present application can be understood according to the specific meaning in the present application by the person skilled in the art according to the specific circumstances.
[0055] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.
Claims
1. A method for preparing metallographic specimens for CSP devices, characterized in that, Specifically, the following steps are included: Two symmetrical triangular elastic thin film clips are used to clamp the left and right ends of the CSP device respectively, so as to fix it in the first inlay mold. The first inlay material is used to fill the first inlay mold. One end of the elastic thin film clip gradually narrows to the other end, and the wider end of the elastic thin film clip is flush with one side of the CSP device. The top of the first inlay mold filled with resin inlay material is clamped and fixed in the second inlay mold. Grinding begins from the wider end of the elastic sheet clamp until the end wall of the device housing is removed to expose the chip of the CSP device. A second insert is injected into the housing cavity of the CSP device through the exposed port, so that the second insert completely covers the chip of the CSP device and its flip-chip solder joints; Continue grinding the CSP device. During the grinding process, determine whether the exposed length and angle of the two elastic thin sheet clamps are consistent after grinding. If they are consistent, it proves that the grinding profile of the CSP device is horizontal. If they are inconsistent, adjust the clamping angle of the CSP device in the second inlay mold to grind it in the same direction.
2. The method for preparing a metallographic sample for a CSP device according to claim 1, characterized in that, The elastic sheet clip has a symmetrical structure, including two right-angled triangular sheets and a clamping part. One acute vertex of each of the two right-angled triangular sheets is connected together, and the side between the acute angle and the right angle of the triangle serves as the bottom of the elastic sheet clip. The clamping part is provided between the other right-angled sides of the two triangular sheets. The clamping part matches the CSP device and is used to clamp and fix the CSP device to keep it upright and stable during the first inlay pouring and solidification process.
3. The method for preparing a metallographic sample for a CSP device according to claim 2, characterized in that, During grinding, the bottom of the elastic sheet clamp is flush with the side of the CSP device to be ground, and grinding begins from the bottom of the elastic sheet clamp.
4. The method for preparing a metallographic sample for a CSP device according to claim 2, characterized in that, The flexible sheet clip is made of PET plastic, epoxy resin, or stainless steel.
5. The method for preparing a metallographic sample for a CSP device according to claim 1, characterized in that, The first inlay material is a mixture of denture powder and curing liquid.
6. The method for preparing a metallographic sample for a CSP device according to claim 1, characterized in that, The second insert is a hard material with good fluidity and low expansion and polymerization shrinkage during curing.
7. The method for preparing a metallographic sample for a CSP device according to claim 1, characterized in that, Grinding was performed using a double-disc semi-automatic metallographic grinding and polishing machine loaded with sandpaper. When the chip was fully exposed and the two ends of the elastic thin sheet clamp were flush, polishing was performed using a double-disc semi-automatic metallographic grinding and polishing machine loaded with polishing cloth to obtain an ideal metallographic interface.
8. The method for preparing a metallographic sample for a CSP device according to claim 8, characterized in that, When grinding, the speed of the double-disc semi-automatic metallographic polishing machine is set to 600~1200r / min, and it is used in combination with 320 mesh, 800 mesh and 1200 mesh wet sandpaper from coarse to fine.
9. The method for preparing a metallographic sample for a CSP device according to claim 8, characterized in that, During polishing, the speed of the dual-disc semi-automatic metallographic polishing machine is set to 800~1000 r / min, and short-pile cloth is used in conjunction with diamond spray polishing liquid with particle sizes of 2.5μm and 0.5μm.
10. The method for preparing a metallographic sample for a CSP device according to claim 1, characterized in that, The CSP device has a cavity-sealed structure. The internal chip is connected to the substrate by flip-chip or bonding, and then the chip is covered on the substrate by a shell.