Silver plating dot design method, design system, lead frame, and semiconductor package

Abstract

The application provides a silver-plated dot design method, a design system, a lead frame and a semiconductor package, and relates to the technical field of semiconductor packaging. The volume of a soldering end cap is obtained, the shape of a silver-plated dot cross section is set, the size parameters of the silver-plated dot cross section are calculated according to a preset soldering thickness, the cross section size of the silver-plated dot can be reasonably designed, the surface of the lead frame in the soldering area is prevented from being oxidized, the soldering spreading area is prevented from being too large, the soldering thickness is prevented from being too low, the tensile strength of the soldering point position is ensured, the packaging soldering yield is improved, and the reliability of the product is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, and in particular to a silver plating point design method, design system, lead frame, and semiconductor package. Background Technology

[0002] Wire bonding (WB) uses metal wires to electrically connect the I / O solder joints on the wafer to the external pins on the leadframe, achieving electrical interconnection. Flip chip (FC), on the other hand, deposits copper pillars and solder caps on the I / O solder joints of the wafer, then flips the chip and heats it to bond the molten solder caps to the leadframe. This technology has replaced conventional wire bonding. The FC type QFN package, unlike traditional wire bonding packaging, uses a flip-chip method to solder the chip to the leadframe, thereby enabling the I / O signals to be brought out.

[0003] The QFN package of the FC type does not require bonding on the lead frame surface, so it does not need to be electroplated. There is only a transparent anti-tarnish protective film to prevent surface oxidation. This protective film is prone to cracking and volatilization after being affected by temperature. The exposed lead frame surface is easily contaminated and oxidized, which makes the subsequent flip-chip soldering difficult. The main problems are as follows: First, when solder caps are soldered to leadframes, poor wetting occurs due to copper oxidation on the leadframe surface, leading to poor soldering after reflow soldering, or even cold soldering, which seriously affects product functionality. Because of current limitations in testing equipment, this soldering failure cannot be inspected after the reflow soldering station ends, posing a significant risk of defective products being shipped out, which has a major impact on the yield and quality of the packaging plant. Second, when traditional leadframes with ring-shaped silver plating or full-surface nickel-palladium-gold plating are flip-chip soldered to solder caps on flip-chips, the area of ​​solder spread after melting cannot be controlled, resulting in insufficient solder thickness at the solder joint. This leads to insufficient solder joint strength during tensile testing, seriously affecting product reliability. Summary of the Invention

[0004] The purpose of this invention is to provide a silver plating point design method, design system, lead frame, and semiconductor package to alleviate the technical problems of lead frame surface oxidation in the soldering area, as well as excessively large spread area and insufficient soldering thickness.

[0005] In a first aspect, the silver plating dot design method provided by the present invention includes the following steps:

[0006] Determine the volume of the welded end cap;

[0007] Define the shape of the cross-section of the silver plating point;

[0008] Calculate the dimensional parameters of the cross-section of the silver plating point based on the preset welding thickness.

[0009] In conjunction with the first aspect, the present invention provides a first possible implementation of the first aspect, wherein the step of setting the shape of the cross-section of the silver plating point includes: setting the shape of the cross-section of the silver plating point to be circular.

[0010] In conjunction with the first aspect, the present invention provides a second possible implementation of the first aspect, wherein the step of setting the shape of the cross-section of the silver plating point includes: pre-setting the cross-section of the silver plating point to include: a first semicircular portion, a rectangular portion and a second semicircular portion, wherein one side of the rectangular portion coincides with the straight side of the first semicircular portion, and the opposite side of the rectangular portion coincides with the straight side of the second semicircular portion.

[0011] In conjunction with the second possible implementation of the first aspect, the present invention provides a third possible implementation of the first aspect, wherein the step of calculating the dimensional parameters of the cross-section of the silver plating point includes:

[0012] Establish the formula for the volume of the end cap: Wherein, H is the preset welding thickness, R is the radius of the first semicircle and the second semicircle, gap is the difference between the upper and lower base radii of the column formed after the welding cap melts and solidifies, and L is the length of the rectangular part;

[0013] The radii of the first semicircle and the second semicircle are calculated.

[0014] In a second aspect, the design system provided by the present invention includes: an interactive device and a processor connected to the interactive device, the processor being configured to execute a computer program corresponding to the silver plating point design method described in the first aspect.

[0015] Thirdly, the lead frame provided by the present invention has a plurality of silver-plated dots on its surface, the plurality of silver-plated dots being spaced apart and corresponding one-to-one with a plurality of solder end caps;

[0016] The cross-sectional shape of the silver plating point is circular;

[0017] Alternatively, the cross-section of the silver-plated point includes: a first semicircular portion, a rectangular portion, and a second semicircular portion, wherein one side of the rectangular portion coincides with the straight side of the first semicircular portion, and the opposite side of the rectangular portion coincides with the straight side of the second semicircular portion.

[0018] In conjunction with the third aspect, the present invention provides one possible implementation of the third aspect, wherein the cross-sectional dimensions of the silver-plated point satisfy the following formula:

[0019] Wherein, H is the preset welding thickness, R is the radius of the first semicircle and the second semicircle, gap is the difference between the upper and lower base radii of the column formed after the welding cap melts and solidifies, and L is the length of the rectangular part.

[0020] Fourthly, the semiconductor package provided by the present invention includes: a wafer, copper pillars, solder caps, and the lead frame described in the third aspect;

[0021] The wafer surface is connected to a plurality of copper pillars, which are spaced apart, and each copper pillar has a solder cap at the end away from the wafer.

[0022] The multiple welding end caps are fused one-to-one with the multiple silver-plated points.

[0023] In conjunction with the fourth aspect, the present invention provides a first possible implementation of the fourth aspect, wherein the cross-sectional shape of the end of the copper pillar that engages the welding cap is the same as the cross-sectional shape of the silver plating point.

[0024] In conjunction with the first possible implementation of the fourth aspect, the present invention provides a second possible implementation of the fourth aspect, wherein the cross-sectional area of ​​the end of the copper pillar that engages with the welding end cap is smaller than the cross-sectional area of ​​the silver plating point.

[0025] The embodiments of the present invention bring the following beneficial effects: by knowing the volume of the welding end cap and setting the shape of the cross-section of the silver plating point, the size parameters of the cross-section of the silver plating point are calculated according to the preset welding thickness. Thus, the cross-sectional size of the silver plating point can be reasonably designed. On the one hand, oxidation of the lead frame surface in the welding area can be avoided, and on the other hand, the welding spread area can be avoided to avoid the welding thickness to be too low, thereby ensuring the tensile strength of the welding point.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of the present invention, the drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the lead frame provided in an embodiment of the present invention;

[0029] Figure 2This is a schematic diagram of a semiconductor package before soldering, provided in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the semiconductor package in the initial contact between the solder cap and the silver plating point, as provided in an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of a semiconductor package after soldering is completed, provided in an embodiment of the present invention.

[0032] Figure 5 A schematic diagram of a silver plating point provided in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of another silver plating point provided in an embodiment of the present invention.

[0034] Icons: 100 - Solder cap; 200 - Silver plating point; 210 - First semicircle; 220 - Rectangular section; 230 - Second semicircle; 300 - Lead frame; 400 - Wafer; 500 - Copper pillar; 600 - Pin; 700 - Bare copper. Detailed Implementation

[0035] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Physical quantities in formulas, unless otherwise specified, should be understood as basic quantities in the International System of Units (SI), or derived quantities derived from basic quantities through mathematical operations such as multiplication, division, differentiation, or integration.

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the silver plating point design method provided in this embodiment of the invention includes the following steps:

[0039] The volume of the welding end cap 100 is known;

[0040] Define the shape of the cross-section of the silver plating point 200;

[0041] Calculate the dimensional parameters of the cross-section of the silver plating point 200 based on the preset welding thickness.

[0042] The silver plating point design method described in this embodiment utilizes the principle that the volume of the welding end cap 100 remains unchanged before and after welding. By setting the shape of the cross-section of the silver plating point 200, the area of ​​the joint surface to be joined to the silver plating point 200 after welding is determined. The dimensional parameters of the cross-section of the silver plating point 200 are simulated and calculated based on the preset welding thickness. Therefore, during flip-chip welding, there is no need to blindly design the cross-section of the silver plating point 200. This avoids oxidation of the lead frame 300 surface in the welding area and prevents the welding spread area from being too large, thus avoiding an excessively thin solidified structure after the welding end cap 100 melts, thereby ensuring the tensile strength of the weld joint.

[0043] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5As shown, in this embodiment of the invention, the step of setting the shape of the cross-section of the silver-plated point 200 includes setting the shape of the cross-section of the silver-plated point 200 to be circular. Preferably, the cross-section of the silver-plated point 200 is the same as the cross-section of the end of the welding cap 100 of the copper pillar 500. Under the condition that both are set to be circular, during welding, the multiple copper pillars 500 and the multiple silver-plated points 200 are coaxially arranged in a one-to-one correspondence. During the welding process, the welding cap 100 is heated to a molten state, and the molten welding cap 100 diffuses and joins the surface of the silver-plated point 200. The area of ​​the welding cap 100 that is wetted and spread is limited to the range of the silver-plated point 200, thereby avoiding the molten welding cap 100 spreading too large an area, and thus avoiding welding defects such as skewing, cold welding, or incomplete welding at the weld point position.

[0044] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 6 As shown, the steps for setting the shape of the cross-section of the silver plating point 200 include: the cross-section of the silver plating point 200 includes: a first semicircular portion 210, a rectangular portion 220 and a second semicircular portion 230, one side of the rectangular portion 220 coincides with the straight side of the first semicircular portion 210, and the opposite side of the rectangular portion 220 coincides with the straight side of the second semicircular portion 230.

[0045] Specifically, the diameters of the first semicircular portion 210 and the second semicircular portion 230 are equal to the width of the rectangular portion 220. During welding, the molten welding end cap 100 is immersed in the surface of the silver-plated point 200. When the length of the rectangular portion 220 is shortened to near zero, the first semicircular portion 210 and the second semicircular portion 230 are spliced ​​together to form an approximately circular structure.

[0046] In this embodiment, the steps for calculating the dimensional parameters of the cross-section of the silver plating point 200 include:

[0047] Establish the formula for the volume of the end cap: Wherein, H is the preset welding thickness, R is the radius of the first semicircular part 210 and the second semicircular part 230, gap is the difference between the upper and lower base radii of the column formed by the melting and solidification of the welding end cap 100, and L is the length dimension of the rectangular part 220.

[0048] The radii of the first semicircle 210 and the second semicircle 230 are calculated.

[0049] In the calculation process, the preset weld thickness H is selected within a range that matches the weld strength, thus preventing the structure thickness from being too thin after the weld cap 100 melts and solidifies. Tin is typically used as the welding material for the weld cap 100. The molten weld cap 100 will not cause oxidation of the silver plating points 200, thereby protecting the copper lead frame 300.

[0050] The design system provided in this embodiment of the invention includes: an interactive unit and a processor connected to the interactive unit, the processor being used to execute a computer program corresponding to the above-described silver plating point design method.

[0051] Furthermore, the design system also includes a memory that stores a computer program corresponding to the above-mentioned silver plating point design method. The memory is connected to a processor. The preset welding thickness is input through an interactive interface, and the shape of the cross-section of the silver plating point 200 is selected. The volume of the welding end cap 100 and the preset welding thickness are substituted into the above-mentioned end cap volume formula, thereby calculating the length of the rectangular part 220, the radius of the first semicircular part 210, and the radius of the second semicircular part 230.

[0052] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the lead frame provided in this embodiment of the invention has a plurality of silver-plated dots 200 on its surface. The plurality of silver-plated dots 200 are spaced apart and correspond one-to-one with a plurality of solder caps 100. The cross-sectional shape of the silver-plated dots 200 is circular. Alternatively, the cross-section of the silver-plated dots 200 includes: a first semicircular portion 210, a rectangular portion 220 and a second semicircular portion 230. One side of the rectangular portion 220 coincides with the straight side of the first semicircular portion 210, and the opposite side of the rectangular portion 220 coincides with the straight side of the second semicircular portion 230.

[0053] In this embodiment of the invention, the dimensions of the cross-section of the silver plating point 200 satisfy the following formula:

[0054] Wherein, H is the preset welding thickness, R is the radius of the first semicircle 210 and the second semicircle 230, gap is the difference between the upper and lower base radii of the column formed by the melting and solidification of the welding end cap 100, and L is the length of the rectangular part 220. The silver plating point 200 designed accordingly ensures that the structural thickness formed by the melting and solidification of the welding end cap 100 reaches the preset welding thickness, avoiding the technical problem of the welding end cap 100 spreading out too large after melting, thereby preventing insufficient tensile strength at the weld point due to excessively thin welding thickness.

[0055] like Figure 1 , Figure 2 , Figure 3 and Figure 4As shown, the semiconductor package provided in this embodiment of the invention includes: a wafer 400, copper pillars 500, solder caps 100, and the aforementioned lead frame 300; multiple copper pillars 500 are connected to the surface of the wafer 400, and the multiple copper pillars 500 are spaced apart, with a solder cap 100 provided at the end of each copper pillar 500 facing away from the wafer 400; the multiple solder caps 100 are fused one-to-one with multiple silver-plated points 200. The lead frame 300 has multiple independent and unconnected pins 600, each pin 600 including bare copper 700 and a silver-plated point 200 plated on the surface of the bare copper 700. The cross-section of the silver-plated point 200 is designed according to the above embodiment so that the thickness of the solder cap 100 when it is immersed and joined to the silver-plated point 200 meets the set requirements, thereby avoiding excessively low solder joint thickness and ensuring that the solder joint strength meets the design requirements during tensile testing, thus improving the product reliability of the semiconductor package.

[0056] Furthermore, the cross-sectional shape of the end of the copper pillar 500 and the welding cap 100 is the same as the cross-sectional shape of the silver plating point 200. The molten welding cap 100 extends from the copper pillar 500 and wets and joins the silver plating point 200. The cross-sectional shape of the end of the copper pillar 500 is the same as the cross-sectional shape of the silver plating point 200. This can prevent the welding cap 100 from solidifying after melting and forming a twisted or skewed structure, thereby reducing the welding defect rate.

[0057] Furthermore, the cross-sectional area of ​​the end of the copper pillar 500 joined to the welding cap 100 is smaller than the cross-sectional area of ​​the silver plating point 200. The molten welding cap 100 extends from the copper pillar 500 and wets and joins the silver plating point 200. After melting, the welding cap 100 solidifies to form a frustum structure, resulting in higher welding strength and improved welding quality and reliability.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing silver-plated dots, characterized in that, Includes the following steps: The volume of the welded end cap (100) is known; Define the shape of the cross-section of the silver plating point (200); Calculate the dimensional parameters of the cross-section of the silver plating point (200) based on the preset welding thickness; The step of setting the shape of the cross-section of the silver plating point (200) includes: presetting the cross-section of the silver plating point (200) to include: a first semicircular part (210), a rectangular part (220) and a second semicircular part (230), wherein one side of the rectangular part (220) coincides with the straight side of the first semicircular part (210), and the opposite side of the rectangular part (220) coincides with the straight side of the second semicircular part (230); The step of calculating the dimensional parameters of the cross-section of the silver plating point (200) includes: Establish the formula for the volume of the end cap: Wherein, H is the preset welding thickness, R is the radius of the first semicircular part (210) and the second semicircular part (230), gap is the difference between the upper and lower base radii of the column formed by the melting and solidification of the welding end cap (100), and L is the preset length dimension of the rectangular part (220); The radii of the first semicircular portion (210) and the second semicircular portion (230) are calculated.

2. A design system, characterized in that, include: An interactive device and a processor connected to the interactive device, the processor being configured to execute a computer program corresponding to the silver plating dot design method of claim 1.

3. A lead frame, characterized in that, The surface of the lead frame (300) is provided with a plurality of silver-plated dots (200), which are spaced apart and correspond one-to-one with a plurality of solder caps (100); The cross-section of the silver-plated point (200) includes: a first semicircular portion (210), a rectangular portion (220) and a second semicircular portion (230), wherein one side of the rectangular portion (220) coincides with the straight side of the first semicircular portion (210), and the opposite side of the rectangular portion (220) coincides with the straight side of the second semicircular portion (230); The dimensions of the cross-section of the silver-plated point (200) satisfy the following formula: Wherein, H is the preset welding thickness, R is the radius of the first semicircular part (210) and the second semicircular part (230), gap is the difference between the upper and lower base radii of the column formed by the melting and solidification of the welding end cap (100), and L is the preset length dimension of the rectangular part (220).

4. A semiconductor package, characterized in that, include: The wafer (400), copper pillar (500), solder cap (100), and lead frame as described in claim 3; The wafer (400) has multiple copper pillars (500) connected to its surface. The copper pillars (500) are spaced apart, and each copper pillar (500) has a solder cap (100) at its end away from the wafer (400). The multiple welding end caps (100) are fused one-to-one with the multiple silver-plated points (200).

5. The semiconductor package according to claim 4, characterized in that, The cross-section of the end of the copper pillar (500) that joins the welding end cap (100) has the same cross-sectional shape as the silver plating point (200).

6. The semiconductor package according to claim 5, characterized in that, The cross-sectional area of ​​the end of the copper pillar (500) that is joined to the welding end cap (100) is smaller than the cross-sectional area of ​​the silver plating point (200).

Images