Lead frame

Abstract

A lead frame which can be used for semiconductor package manufacturing, has a plurality of external connection terminals, a surface which is exposed to a side where the lead frame and an external device are connected, and a side surface, a region of the external connection terminals which becomes a lead in the surface side is provided with a recess, the depth of the recess is half or more of the thickness of the lead, and a side edge is provided at a predetermined position between the center in the thickness direction of the lead and the surface of the lead on the side surface of the lead in the portion where the recess is formed. Thereby, the opening area of the door shape which is a part where the solder connection part of the semiconductor package can be visually recognized can be maximized, while deformation caused by a decrease in the strength of the lead can be prevented.

Description

Technical Field

[0001] The present invention relates to a lead frame that can be used in semiconductor packaging, wherein the semiconductor package is a surface-connected semiconductor package in which external connection terminals on the back side of the semiconductor package are connected to external devices such as printed circuit boards. Background Technology

[0002] When assembling semiconductor packages to external devices, visual inspection of the solder joints between the semiconductor package and the external device is required to determine their quality.

[0003] In the past, semiconductor packages without external leads, such as QFN (Quad-Flat No-leaded) type, had external connection terminals arranged on the back side of the semiconductor package. This resulted in a structure that connected multiple external connection terminals exposed on the back side of the semiconductor package to external devices such as printed circuit boards. Therefore, it was difficult to visually inspect whether solder joints had been made.

[0004] However, if visual inspection of the solder joints is not possible, inherent connection defects during the soldering process may be missed, and the costs of discovering these defects only during subsequent power-on checks will be significantly higher. Furthermore, while X-rays can be used to inspect solder joints, this increases the cost of the X-ray equipment.

[0005] Therefore, Patent Document 1 discloses the following technology: a recess is provided inside a predetermined area on one side (back side) of the lead frame, which includes the area of ​​the external connection terminal that becomes the lead, and the boundary line of the cut area is crossed. After the front side is sealed with resin, a cutting process is performed at the position where the cross section of the recess is exposed, thereby forming a solder connection portion that can be visually viewed from the external connection terminal exposed on the side of the semiconductor package.

[0006] [Background Technical Documents]

[0007] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-200994 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] According to the technology described in Patent Document 1, which makes the exposed surface of the external connection terminal into a door shape, although a space where the solder connection part can be visually viewed can be obtained, in recent years, it has been desired to further increase the opening area of ​​the side that becomes a door shape in order to make it as easy as possible to visually view the solder connection part.

[0011] If the opening area of ​​the external connection terminal in the form of a door is maximized in order to facilitate visual inspection of the solder joint, the following concerns arise: because the lead wire is locally thinned, its strength may be insufficient, and it may deform during lead frame manufacturing or semiconductor package assembly.

[0012] The present invention was developed in view of the aforementioned prior art problems, and its purpose is to provide a lead frame that can maximize the opening area of ​​the solder joint portion of the semiconductor package that is configured to be visible, i.e., the door-shaped opening, while preventing deformation caused by a decrease in lead strength.

[0013] [Methods used to solve problems]

[0014] To achieve the above objectives, the lead frame of the present invention can be used in semiconductor packaging manufacturing, having a plurality of external connection terminals exposed on a side surface and a side surface on which the lead frame is connected to an external device, and the area of ​​the external connection terminal that becomes a lead on one side of the lead frame having a recess, the depth of which is more than half the thickness of the lead, and a side edge having a predetermined position between the center of the lead in the thickness direction and one side surface of the lead on the side surface where the recess is formed.

[0015] [The effects of the invention]

[0016] According to the lead frame of the present invention, the lead side surface of the portion of the recess formed with a depth of more than half the thickness of the lead has a side edge at a predetermined position between the center of the lead in the thickness direction and one side of the lead, thereby reinforcing the portion that is thinned due to the formation of the recess and preventing deformation of the lead during the manufacturing process.

[0017] Therefore, according to the lead frame of the present invention, a lead frame can be provided that can maximize the opening area of ​​the door shape at the part where the solder connection portion of the semiconductor package can be visually viewed, while preventing deformation caused by a decrease in the strength of the lead. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view showing an example of a lead wire in a recessed position of a lead frame according to an embodiment of the present invention.

[0019] Figure 2 This is an explanatory diagram showing the sample preparation steps in the pre-lead formation stage of the lead frame of the embodiments and comparative examples of the present invention.

[0020] Figure 3 Is it for display use Figure 2An explanatory diagram illustrating the steps of using the prepared sample to form the lead frame of Example 1.

[0021] Figure 4 Is it for display use Figure 2 An explanatory diagram illustrating the steps of using the prepared sample to form the leads of the lead frame in Example 2.

[0022] Figure 5 Is it for display use Figure 2 A diagram illustrating the steps of using the prepared sample to form the lead wires of the lead frame in Comparative Example 1.

[0023] Figure 6 This is a cross-sectional view showing an example of a lead wire in a recessed position of a conventional lead frame. Detailed Implementation

[0024] Implementation Form 1

[0025] The lead frame of this embodiment is a lead frame that can be used in semiconductor packaging manufacturing. It has multiple external connection terminals exposed on the surface and side of the lead frame where it connects to external devices, such as... Figure 1 As shown, on one side (in) Figure 1 The area in the lower part of the paper (the middle part) that serves as the external connection terminal for the lead wire 11 has a recess 12.

[0026] The recess 12 has a width of about half the width of the lead wire 11 and a depth of about half the thickness (t) of the lead wire 11 (t / 2).

[0027] On the side of the lead 11 where the recess 12 is formed, at the center in the thickness direction of the lead 11 (that is, Figure 1 A side edge A is provided at a predetermined position between the position (which is half the thickness (t) of the lead 11, i.e., at the position between the position of the lead 11 and one side of the lead 11) and a predetermined position (in other words, at the position between the position of the lead 11 and the position of the lead 11) and a predetermined position between the position of the lead 11 and one side of the lead 11. Figure 1 When the distance from the vertex of the side edge A to one side of the lead 11 is set to LA, a side edge A will be formed at a position where LA≦t / 2.

[0028] When a lead frame is manufactured by etching a metal plate, a chemical solution is used to etch both sides of the metal plate to dissolve and remove unwanted parts of the metal plate, thereby forming the shape of the lead frame.

[0029] This etching process is performed by studying the processing conditions to make the sides of the resulting lead frame nearly straight (the lead cross-section is rectangular). Furthermore, by etching from both sides of the metal plate, small protrusions known as side edges can be formed on the sides of the lead frame at approximately the center of the plate thickness.

[0030] In previous lead frames, such as Figure 6 As shown, the side edge A formed on the side surface of the portion forming the recess 12 in the lead 11 is formed at the central position in the lead thickness direction (in other words, when from...). Figure 6 When the distance from the vertex of the side edge A to one side of the lead 11 is set to LA', the side edge A will be formed at the position LA' = t / 2.

[0031] However, the side of the portion in lead 11 where the recess 12 is formed becomes a thin wall. Therefore, in such a case... Figure 6 In the conventional leadframe shown, if the opening of the recess 12 is increased in the width direction of the lead 11 in order to facilitate visual inspection of the solder joint, the following concerns arise: the side strength of the portion of the lead 11 in which the recess 12 is formed is insufficient, and deformation occurs during leadframe manufacturing or semiconductor package assembly.

[0032] The lead frame of the present invention enhances the strength of the side of the portion where the recess 12 is formed by setting the protrusion to a predetermined position between the center of the lead thickness and one side of the lead.

[0033] According to the lead frame of this embodiment, since the side of the lead 11 in the portion of the recess 12 formed with a depth of more than half (t / 2) of the thickness (t) of the lead 11, from the center in the thickness direction of the lead 11 (that is, Figure 1 The predetermined position between half (t / 2) of the thickness (t) of the middle lead 11 and one side of the lead 11 is provided with a side edge A, so that the part that is thinned by forming the recess 12 can be reinforced, and even if the opening area of ​​the recess is increased in the width direction of the lead 11 in order to facilitate visual inspection of the solder joint, deformation of the lead 11 during the manufacturing process can still be prevented.

[0034] Therefore, according to the lead frame of this embodiment, a lead frame can be obtained that can maximize the opening area of ​​the door shape of the part that is a part of the solder connection of the semiconductor package that can be visually viewed, while preventing deformation caused by the reduction of lead strength.

[0035] [Example]

[0036] <Sample Preparation>

[0037] Use a copper strip metal plate 10 with a thickness of 0.2 mm (refer to...) Figure 2 (a)), and an anti-corrosion layer is formed on both sides.

[0038] Next, exposure and development are performed to form an etching resist mask 31, which covers the entire surface on one side and forms a recess at a predetermined position on one side (see reference). Figure 2 (b)).

[0039] Next, an etching process is performed to form a recess 12 at a predetermined position on one side, the recess 12 being half the width of the lead wire (see reference). Figure 2 (c) The depth of the recess 12 is set to half the thickness of the plate (0.1 mm).

[0040] Next, remove the etching resist mask 31 (see reference). Figure 2 (d)).

[0041] Next, an anti-corrosion layer is formed on both sides of the strip metal plate 10 with recesses.

[0042] Furthermore, exposure and development are performed to form a resist mask 32 for forming the plating layer at predetermined positions on both sides (see reference). Figure 2 (e). Furthermore, in Figure 2 (e) For convenience, the opening for forming the plating layer is shown only on one side of the plating resist mask 32.

[0043] Next, a plating layer 13 of predetermined thickness is formed on the surface of the strip metal plate 10 exposed from the opening of the plating resist mask 32, in the order of Ni (nickel), Pd (palladium), and Au (gold).

[0044] Subsequently, a strip metal plate sample S was prepared by removing the anti-corrosion mask 32 used for plating.

[0045] <Example 1>

[0046] Anti-corrosion layers are formed on both sides of the strip metal sample S.

[0047] Next, exposure and development are performed to form an etching resist mask 33 on both sides for forming the lead frame.

[0048] At this time, a correction portion 33a is provided on one side of the etching resist mask 33. The correction is a correction to suppress etching on the side of the lead 11 where the recess 12 is formed (see reference). Figure 3 (a)).

[0049] Next, an etching process is performed to form the predetermined lead frame shape (see reference). Figure 3 (b)).

[0050] Subsequently, by removing the etching resist mask 33, the lead frame of Example 1 is obtained (see Figure 1). Figure 3 (c)).

[0051] On the side of the lead frame of the obtained embodiment 1, the side edge exists at approximately the center position in the overall thickness direction of the lead frame, wherein, on the side of the portion of the lead 11 where the recess 12 is formed, the side edge A exists at approximately 0.055 to 0.075 mm from one side.

[0052] Prepare 1600 lead wires 11 with side edges A formed on the side of the portion with recess 12 in the lead frame of Embodiment 1, and visually inspect for deformation.

[0053] In the lead frame of Example 1, the lead deformation rate was 0% (out of 1600 leads, the number of deformed leads was 0).

[0054] <Example 2>

[0055] Anti-corrosion layers are formed on both sides of the strip metal sample S.

[0056] Next, exposure and development are performed, and etching resist masks 33 for forming lead frames are formed on both sides.

[0057] At this point, the etching resist mask 33 on the other side is configured such that the opening area is smaller than that of the etching resist mask 33 on one side (see reference). Figure 4 (a)).

[0058] Next, a chemical solution was sprayed onto the other side only, and etching was performed to a depth of 0.065 mm (see reference). Figure 4 (b)) and then perform etching on both sides to form the predetermined lead frame shape (see reference). Figure 4 (c)).

[0059] Subsequently, the lead frame of Example 2 is obtained by removing the etching resist mask (see Figure 2). Figure 4 (d)).

[0060] On the side of the lead frame of the obtained embodiment 2, the side edge A is formed on the side of the portion of the lead 11 in which the recess 12 is formed, and the side edge generally exists at a distance of about 0.06 to 0.08 mm from one side.

[0061] Prepare 1600 lead wires 11 with side edges A formed on the side of the portion with recess 12 in the lead frame of embodiment 2, and visually inspect for deformation.

[0062] The visual inspection results showed that the lead deformation rate in the lead frame of Example 2 was 0% (out of 1600 leads, the number of deformed leads was 0).

[0063] <Comparative Example 1>

[0064] Anti-corrosion layers are formed on both sides of the strip metal sample S.

[0065] Next, exposure and development are performed, and as with conventional products, etching resist masks 33 for forming the lead frame are formed on both sides (see reference). Figure 5 (a)).

[0066] Next, an etching process is performed to form the predetermined lead frame shape (see reference). Figure 5 (b)).

[0067] Subsequently, by removing the etching resist mask 33, the lead frame of Comparative Example 1 (see reference) is obtained. Figure 5 (c)).

[0068] The side of the lead frame of Comparative Example 1 is included in the side edge A formed by the side of the portion of the lead 11' where the recess 12 is formed, and the side edge is located at approximately the center in the overall thickness direction of the lead frame.

[0069] Prepare 1600 leads 11' with side edges A formed on the side of the portion with recess 12 in the lead frame of Comparative Example 1, and visually inspect for deformation.

[0070] In the lead frame of Comparative Example 1, the lead deformation rate was 1.75% (out of 1600 leads, the number of deformed leads was 28).

[0071] The preferred embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments and examples, and various modifications and substitutions can be made to the above embodiments and examples without departing from the scope of the present invention.

[0072] For example, the lead frame of the embodiment of the present invention can also be obtained by the following manufacturing method: a semi-etching process is performed on the other side of the strip metal plate 10 to thin a predetermined area on the outside of the part corresponding to the lead frame, and an etching process is performed on the strip metal plate sample S, which has been etched on one side to form a recess 12, to form the lead frame from both sides.

[0073] [Industrial Applicability]

[0074] The lead frame of the present invention is useful in fields where visualization of solder joints is required.

Claims

1. A lead frame for semiconductor packaging manufacturing, having a plurality of external connection terminals exposed on the side where the lead frame connects to external devices, characterized in that: Each terminal has a side surface connected to the outside, a top side opposite to the side surface, a recess forming an opening from the side surface toward the top side, a side surface connecting the top side and the side surface, located outside the recess and surrounding the recess, and a side edge protruding from the side surface toward the opening, wherein the thickness from the side surface to the top side is t, the depth of the recess is not less than t / 2, and the distance from the vertex of the side edge to the top side is less than t / 2.

Images