Methods to reduce the risk of cold solder joints
By increasing the high-temperature heating chamber temperature and formic acid concentration in the reflow machine table, the surface roughness of the electroplating alloy ball caused by the reduction of chip size is solved, and the quality of reflow soldering and electrical connection performance are improved.
Patent Information
- Application Number
- CN202411963437.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-30
- Publication Date
- 2025-04-04
AI Technical Summary
As the chip size and interconnected solder joint size decrease, the roughness of the surface of the electroplated alloy ball affects the quality and conduction current performance of the reflow solder, and the prior art has high cost and long verification cycles when batch changes and material changes.
A reflux machine treatment method is adopted, including a preheating chamber, a high-temperature heating chamber, a first cooling chamber, a second cooling chamber and a cooling chamber, to increase the temperature of the high-temperature heating chamber to 280°C to 320°C, and to increase the formic acid concentration to 98% to remove oxides on the surface of the chip part.
By increasing the temperature of the high-temperature heating chamber and formic acid concentration, the surface of the chip can be smoother, the quality of reflow soldering is improved, the risk of dummy soldering is reduced, and the electrical connection performance can be enhanced.
Smart Images
Figure CN119747779A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of packaging preparation technology, and in particular to a method for reducing the risk of cold solder joints. Background Art
[0002] At present, as the chip size, interconnect solder joint size, and pitch become smaller and smaller, electroplated alloy balls are generally made first, and then flip-chip reflow soldering is performed to achieve interconnection. The influence of the alloy ball surface quality in the flip-chip soldering reflow soldering process in the back end of advanced packaging cannot be ignored. The packaging level will affect the quality of the alloy ball reflow soldering. In terms of electrical performance, the rough alloy ball surface will affect the on-current performance.
[0003] Optimizing the quality of electroplated alloy balls usually involves adjusting electroplating additives and the metal ratio of alloy balls. However, changes in batch size and materials have a certain impact on cost, verification and introduction cycle economy, efficiency, and process. Summary of the invention
[0004] In order to solve the above technical problem or at least partially solve the above technical problem, the present application provides a method for reducing the risk of cold solder joints.
[0005] The present application embodiment provides a method for reducing the risk of cold solder joints, including:
[0006] After the electroplating is completed, the chip parts are reflowed in a reflow machine, and the reflow machine includes a preheating chamber, a high-temperature heating chamber, a first cooling chamber, a second cooling chamber and a cooling chamber. The chip parts enter the preheating chamber, the high-temperature heating chamber, the first cooling chamber, the second cooling chamber and the cooling chamber in sequence for reflow treatment, and the temperature of the high-temperature heating chamber is increased to T2, 280℃≤T2≤320℃, and at the same time, the concentration of formic acid used to remove oxidation on the surface of the chip parts during the reflow treatment is increased.
[0007] In some embodiments, the step of increasing the concentration of formic acid used to remove oxidation on the surface of the chip during the reflow process is to increase the concentration of formic acid from 95% to 98%.
[0008] In some embodiments, the heating time t2 of the chip component in the high temperature heating chamber is shortened, 18s≤t2≤22s.
[0009] In some embodiments, the temperature of the preheating chamber is increased to T1, 190°C≤T1≤200°C.
[0010] In some embodiments, the heating time t1 of the chip component in the preheating chamber is shortened, 28s≤t1≤32s.
[0011] In some embodiments, the temperature of the first cooling chamber is increased to T3, 230°C≤T3≤250°C.
[0012] In some embodiments, the cooling time t3 of the chip component in the first cooling cavity is extended, 55s≤t3≤65s.
[0013] In some embodiments, the temperature of the second cooling chamber is increased to T4, 180°C≤T4≤200°C.
[0014] In some embodiments, the cooling time t4 of the chip component in the second cooling cavity is extended, 28s≤t4≤32s.
[0015] In some embodiments, the preheating chamber, the high-temperature heating chamber, the first cooling chamber, the second cooling chamber, and the cooling chamber are passed through N2 to maintain the temperature inside the corresponding chambers.
[0016] Compared with the prior art, the technical solution provided by the embodiments of the present application has the following advantages:
[0017] The method for reducing the risk of cold solder joints provided in the embodiment of the present application is that the chip parts after electroplating are reflowed through a reflow machine, and the reflow machine includes a preheating chamber, a high-temperature heating chamber, a first cooling chamber, a second cooling chamber and a cooling chamber. The chip parts enter the preheating chamber, the high-temperature heating chamber, the first cooling chamber, the second cooling chamber and the cooling chamber in sequence for reflow treatment, and the temperature of the high-temperature heating chamber is increased to T2, 280℃≤T2≤320℃, and at the same time, the concentration of formic acid used to remove oxidation on the surface of the chip parts during the reflow treatment is increased.
[0018] By increasing the temperature T2 of the high-temperature heating chamber of the reflow machine, it is beneficial to volatilize the metal crystals on the surface of the chip (SnAg metal layer), and to increase the concentration of formic acid used to remove oxidation on the surface of the chip during the reflow process, so as to better treat the metal crystals on the surface of the chip. It can make the surface of the chip smoother after electroplating, thereby improving the quality of reflow soldering, reducing the risk of cold soldering in the back-end flip-chip reflow soldering, and enhancing the electrical performance of the connection. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.
[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0021] Figure 1 A schematic diagram of the distribution of various cavities of the reflow machine described in an embodiment of the present application;
[0022] Figure 2 A schematic diagram of the SnAg metal layer of a chip component after the chip component electroplating is completed and before reflow as described in an embodiment of the present application;
[0023] Figure 3 Schematic diagram of the SnAg metal layer of the chip after reflow treatment in Experiment 1;
[0024] Figure 4 Schematic diagram of the SnAg metal layer of the chip component after reflow treatment in Experiment 2.
[0025] Among them, S1, preheating cavity; S2, high temperature heating cavity; S3, first cooling cavity; S4, second cooling cavity; S5, cooling cavity; 1-1, SnAg metal layer; 2, metal crystals. DETAILED DESCRIPTION
[0026] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the scheme of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.
[0027] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only part of the embodiments of the present application, rather than all of the embodiments.
[0028] At present, as the chip size, interconnect solder joint size, and pitch become smaller and smaller, electroplated alloy balls are generally made first, and then flip-chip reflow soldering is performed to achieve interconnection. The influence of the alloy ball surface quality in the flip-chip soldering reflow soldering process in the back end of advanced packaging cannot be ignored. The packaging level will affect the quality of the alloy ball reflow soldering. In terms of electrical performance, the rough alloy ball surface will affect the on-current performance.
[0029] Optimizing the quality of electroplated alloy balls usually involves adjusting electroplating additives and the metal ratio of alloy balls. However, changes in batch size and materials have a certain impact on cost, verification and introduction cycle economy, efficiency, and process.
[0030] In view of this, if Figure 1As shown, the embodiment of the present application provides a method for reducing the risk of cold solder joints, including: the chip component after electroplating includes a SnAg metal layer 1, and is reflowed through a reflow machine, the reflow machine includes a preheating chamber S1, a high temperature heating chamber S2, a first cooling chamber S3, a second cooling chamber S4 and a cooling chamber S5, the chip component sequentially enters the preheating chamber S1, the high temperature heating chamber S2, the first cooling chamber S3, the second cooling chamber S4 and the cooling chamber S5 for reflow treatment, and the temperature of the high temperature heating chamber S2 is increased to T2, 280°C≤T2≤320°C, preferably T2 is 300°C, the melting temperature is high, which is conducive to the volatilization of the metal crystals 2 on the surface of the chip component (SnAg metal layer 1). At the same time, the concentration of formic acid used to remove oxidation on the surface of the chip component during the reflow treatment is increased.
[0031] The method for reducing the risk of cold solder joints provided in the embodiment of the present application increases the temperature T2 of the high temperature heating chamber S2 of the reflow machine, and 280°C≤T2≤320°C, which is conducive to the volatilization of the metal crystals 2 on the surface of the chip (SnAg metal layer 1), and increases the concentration of formic acid used to remove oxidation on the surface of the chip during the reflow process, so as to better treat the metal crystals 2 on the surface of the chip. The surface of the chip after electroplating can be made smoother, thereby improving the quality of reflow soldering, reducing the risk of cold solder joints in the back-end flip-chip reflow soldering, and enhancing the electrical performance of the connection. The metal crystals 2 on the surface of the SnAg metal layer 1 are also an oxide layer.
[0032] In some embodiments, increasing the concentration of formic acid used to remove surface oxidation of chip components during the reflow process is to increase the concentration of formic acid from 95% to 98%, so as to better remove surface oxidation of chip components.
[0033] In some embodiments, the heating time t2 of the chip in the high temperature heating chamber S2 is shortened, 18s≤t2≤22s, and t2 is preferably 20s, to ensure a smooth surface of the chip while improving the efficiency of the entire reflow process.
[0034] In some embodiments, the temperature of the preheating chamber S1 is increased to T1, 190° C. ≤ T1 ≤ 200° C. T1 is preferably 195° C. This allows the temperature of the chip to rise rapidly during the reflow process, facilitating the reflow process in each subsequent chamber.
[0035] In some embodiments, the heating time t1 of the chip in the preheating chamber S1 is shortened to 28s≤t1≤32s, and t1 is preferably 30s, so that the chip is quickly heated up and then enters the high-temperature heating chamber S2.
[0036] In some embodiments, the temperature of the first cooling chamber S3 is increased to T3, 230°C≤T3≤250°C, T3 is preferably 240°C, and a high melting temperature is conducive to the volatilization of the metal crystals 2 (surface oxide layer) of the chip component.
[0037] In some embodiments, the cooling time t3 of the chip in the first cooling chamber S3 is extended, 55s≤t3≤65s, and t3 is preferably 60s. A longer time is beneficial to the volatilization of the metal crystals 2 of the chip.
[0038] In some embodiments, the temperature of the second cooling chamber S4 is increased to T4, 180° C. ≤ T4 ≤ 200° C., and T4 is preferably 190° C. A high melting temperature is conducive to the volatilization of the metal crystals 2 of the chip components.
[0039] In some embodiments, the cooling time t4 of the chip in the second cooling chamber S4 is extended, 28s≤t4≤32s, and t4 is preferably 30s. A longer time is beneficial to the volatilization of the metal crystals 2 of the chip.
[0040] In some embodiments, the preheating chamber S1, the high temperature heating chamber S2, the first cooling chamber S3, the second cooling chamber S4 and the cooling chamber S5 are maintained at the corresponding chamber temperatures by passing N2. The cost is low and N2 is stable, which will not affect the chemical reaction during the chip reflow process.
[0041] Experimental comparison
[0042] Figure 2 The diagram in FIG. 1 is a schematic diagram of the SnAg metal layer 1-1 after the chip is electroplated but before reflow. Next, the chip is reflowed by the reflow machine. The distribution of each cavity platform (such as Figure 1 shown).
[0043] Experiment 1: Reflow process of chip components in related technologies
[0044] The steps of the reflow treatment process are: enter the cavity → S1 (preheating cavity) preheating at 165℃ for 45s → S2 (high temperature heating cavity) 235℃ for 26s → S3 (first cooling cavity) 200℃ for 25s → S4 (second cooling cavity) 165℃ for 25s → S5 (cooling cavity) 20℃ for cooling → exit the cavity. The temperature of each cavity is ensured by passing N2 to the cavity environment temperature, and formic acid is passed to remove surface oxidation. The formic acid concentration is 95%. The SnAg metal layer 1-2 morphology of the chip after reflow (such as Figure 3 As shown in the figure, due to the inadequate reaction during the reflow process, metal crystals exist on the surface of the SnAg metal layer, which causes the surface to be rough. This results in the phenomenon of false soldering and poor overcurrent capability in the subsequent flip-chip reflow soldering.
[0045] Experiment 2: Reflow Process of the Embodiment of the Present Application
[0046] The steps of the reflux treatment process are: entering the cavity → S1 (preheating cavity) preheating at 195°C for 30s → S2 (high temperature heating cavity) 300°C for 20s → S3 (first cooling cavity) 240°C for 60s → S4 (second cooling cavity) 190°C for 30s → S5 (cooling cavity) 20°C for cooling → exiting the cavity. The temperature of each cavity is ensured by passing N2 to the cavity environment temperature. The preheating cavity and the high temperature heating cavity quickly heat the chip parts, and the temperature of the first cooling cavity and the second cooling cavity is also relatively high, the melting temperature is high, and the time is maintained for a long time, which is conducive to the volatilization of oxides. Formic acid is used to remove surface oxidation. The formic acid concentration is 98%, 2HCOOH+O2→2CO2+2H2O, thereby forming Figure 4 The smooth SnAg metal layer spherical surface 1-3 optimizes the parameters of the package electroplating reflow process without changing the original machine and materials or the process flow, which has low cost and good effect.
[0047] The reflow ball of the chip after optimized electroplating has a smoother surface, a higher tolerance for the back-end board, and is suitable for all advanced packaging processes of electroplating reflow.
[0048] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.
[0049] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for reducing the risk of cold solder joints, characterized in that: include: After the electroplating is completed, the chip parts are reflowed in a reflow machine, and the reflow machine includes a preheating chamber (S1), a high-temperature heating chamber (S2), a first cooling chamber (S3), a second cooling chamber (S4) and a cooling chamber (S5). The chip parts enter the preheating chamber (S1), the high-temperature heating chamber (S2), the first cooling chamber (S3), the second cooling chamber (S4) and the cooling chamber (S5) in sequence for reflow treatment, and the temperature of the high-temperature heating chamber (S2) is increased to T2, 280°C≤T2≤320°C, and at the same time, the concentration of formic acid used to remove oxidation on the surface of the chip parts during the reflow treatment is increased.
2. The method for reducing the risk of cold solder joints according to claim 1, characterized in that: The concentration of formic acid used to remove oxidation on the surface of the chip during the reflow treatment is increased from 95% to 98%.
3. The method for reducing the risk of cold solder joints according to claim 1, characterized in that: The heating time t2 of the chip component in the high-temperature heating chamber (S2) is shortened, 18s≤t2≤22s.
4. The method for reducing the risk of cold solder joints according to claim 1, characterized in that: The temperature of the preheating chamber (S1) is increased to T1, 190°C≤T1≤200°C.
5. The method for reducing the risk of cold solder joints according to claim 4, characterized in that: The heating time t1 of the chip component in the preheating chamber (S1) is shortened, 28s≤t1≤32s.
6. The method for reducing the risk of cold solder joints according to claim 1, characterized in that: The temperature of the first cooling chamber (S3) is increased to T3, 230°C≤T3≤250°C.
7. The method for reducing the risk of cold solder joints according to claim 6, characterized in that: The cooling time t3 of the chip component in the first cooling cavity (S3) is extended, 55s≤t3≤65s.
8. The method for reducing the risk of cold solder joints according to claim 1, characterized in that: The temperature of the second cooling chamber (S4) is increased to T4, 180°C≤T4≤200°C.
9. The method for reducing the risk of cold solder joints according to claim 8, characterized in that: The cooling time t4 of the chip component in the second cooling chamber (S4) is extended, 28s≤t4≤32s.
10. The method for reducing the risk of cold solder joints according to claim 1, characterized in that: The preheating chamber (S1), the high-temperature heating chamber (S2), the first cooling chamber (S3), the second cooling chamber (S4) and the cooling chamber (S5) are connected to maintain the corresponding chamber temperatures by passing N2.