Novel BDMP packaging method for DiFEM radio frequency module

Abstract

A novel BDMP packaging method for a DiFEM radio frequency module comprises the following steps: step S1, planting a gold ball: fixing a wafer to be processed on a carrier to form a tiny gold ball welding spot, welding the gold ball on a bonding pad, cutting off a gold wire, and leaving a complete gold ball welding spot on the bonding pad; step S2, wafer cutting: using a scribing machine to cut the wafer into independent chips along a predetermined cutting channel; s3, chip and switch inversion: inversely installing the SAW chip and the switch on the PCB substrate of the radio frequency module by using an inversion machine through a gold-gold bonding principle; step S4, film covering: a film is attached to the PCB substrate on which the SAW chip and the switch are attached; s5, covering a protective film: attaching the protective film on the surface of the covering film in the step S4, and curing the protective film; and step S6, cutting the PCB substrate: cutting and braiding the cured PCB along the cutting channel to obtain a DiFEM module.

Description

Technical Field

[0001] The invention discloses a BDMP packaging method, in particular to a novel BDMP packaging method for a DiFEM radio frequency module. Background Art

[0002] Domestic RF front-end module manufacturers usually use BDMP packaging to realize RF module packaging. The full name of "BDMP" is "Bare Die Molded Package". This packaging method is to grow solder balls (Bump) on the bare SAW chip, then directly flip it on the substrate, and then injection mold it into a module.

[0003] The process flow for forming solder bumps on SAW wafers is as follows: ① First, the wafer is cleaned to remove surface contaminants and oxide layers. Nickel, palladium, and gold are deposited on the wafer pads (PADs) by chemical plating. These metal layers are very important to ensure good solder joints and prevent tin from diffusing into the solder.

[0004] ②Use specialized equipment (such as screen printing) to precisely apply solder paste on the gold layer. This step is to establish physical and electrical connection points on the wafer to prepare for the subsequent reflow process. Solder paste usually consists of tin solder and flux. Tin solder: usually composed of alloys of tin (Sn) and other metals (such as lead, silver, and copper). The composition of the alloy is selected depending on the required melting point and mechanical properties. The flux is to help remove oxides from the metal surface, reduce surface tension, and enable the solder to flow and adhere better.

[0005] ③Put the wafer into the reflow oven and gradually heat it to above the melting point of the solder paste. During this process, the solder paste melts and forms a dome-shaped solder ball on the metal pad. As the furnace temperature drops, the tin solidifies to form a solid solder joint.

[0006] ④ Use an appropriate solvent or cleaning fluid to clean the wafer to remove flux residue. Dry the wafer thoroughly to ensure that there is no residual cleaning fluid.

[0007] ⑤ Cut the wafer and pack it into tape.

[0008] The main disadvantages of this process are: Ⅰ. Chemical plating is required, which requires high temperature. However, SAW wafers are very thin and are prone to cracking under huge temperature differences. Ⅱ. When implanting solder balls, different steel meshes need to be customized for different types of wafers because solder paste needs to be applied. The production cost is expensive and it is not easy to change the implantation plan. Ⅲ. Some chemical solutions are needed when cleaning the flux, which can easily corrode the Saw filter.

[0009] The process flow of SIP packaging the balled chip into a module is as follows: ① Use the SMT machine to accurately place the SAW filter chip and switch on the PCB substrate. The PCB substrate is brushed with solder paste and then reflow soldered in a reflow oven to fix the filter chip and switch on the substrate.

[0010] ② Attach a 50μm thick TSA film on the PCB substrate to protect the SAW filter to prevent the epoxy resin from entering the cavity in the subsequent Cmolding process.

[0011] ③ Use epoxy resin to extrude and inject the PCB substrate, filter, and switch under pressure.

[0012] ④After curing, use a dicing machine to cut the packaged PCB substrate to obtain individual DiFEM RF modules.

[0013] The main disadvantages of this process are: in the SMT process, the chip after ball implantation needs to be flipped on the substrate. During this process, many process problems will occur when the solder ball is flipped on the substrate, such as voids. Summary of the invention

[0014] In view of the above-mentioned disadvantages of the prior art that BDMP packaging method is usually adopted to realize the packaging of RF modules, and many process problems will occur when the solder balls are flipped onto the substrate, the present invention provides a novel BDMP packaging method for DiFEM RF modules, which uses a ball welding machine to implant gold balls on the wafer instead of a method of implanting solder balls by printing solder paste, and adopts a flip-chip machine for packaging, thereby solving the above-mentioned problems.

[0015] The technical solution adopted by the present invention to solve the technical problem is: a new BDMP packaging method for DiFEM radio frequency module, the packaging method comprising the following steps: Step S1, implanting a gold ball: fix the wafer to be processed on a carrier, heat the gold wire with a torch, melt the end of the gold wire to form a ball, then align the gold ball to a specific pad on the wafer, gently press the gold ball on the pad, and apply ultrasonic vibration at the same time. The ultrasonic vibration and pressure work together to weld the gold ball and the pad together to form a tiny gold ball solder joint. The gold ball is soldered to the pad, and the gold wire is cut off, leaving a complete gold ball solder joint on the pad; Step S2, wafer cutting: using a dicing machine to cut the wafer into individual chips along predetermined cutting paths; Step S3, flip-chipping of the chip and the switch: using a flip-chip machine to flip-chip the SAW chip and the switch onto the PCB substrate of the RF module through the principle of gold-gold bonding; Step S4, laminating: attaching the film to the PCB substrate with the SAW chip and the switch; Step S5, coating with a protective film: attaching a protective film to the coating surface in step S4, and curing the protective film; Step S6, cutting the PCB substrate: cutting and taping the cured PCB along the cutting paths of the PCB to obtain a DiFEM module.

[0016] The technical solution adopted by the present invention to solve the technical problem further includes: In the step S2, a protective layer is applied on the surface of the wafer before the wafer is cut.

[0017] In the step S2, the protective layer on the surface of the wafer is removed after the wafer is cut to obtain the cut chips.

[0018] In the step S1, when implanting the gold balls, two gold balls are implanted continuously at the same position.

[0019] In the step S4, TSA film or epoxy resin film is used for lamination.

[0020] The TSA film or epoxy resin film has a thickness of 50 μm.

[0021] The protective film is made of epoxy resin film or plastic film.

[0022] When the protective film is an epoxy resin film, an oven is used for curing, and the curing temperature of the oven is 150°C to 250°C.

[0023] The beneficial effects of the present invention are as follows: the present invention greatly simplifies the process steps of BDMP packaging and improves production efficiency; reduces the material and energy consumption required in production, and also reduces labor and maintenance costs; reduces the probability of process problems, thereby improving the overall quality and consistency of the product.

[0024] The present invention will be further described below in conjunction with specific implementation modes. DETAILED DESCRIPTION

[0025] This embodiment is a preferred implementation mode of the present invention. Other embodiments whose principles and basic structures are the same or similar to those of this embodiment are within the protection scope of the present invention.

[0026] The present invention mainly protects a novel BDMP packaging method for a DiFEM radio frequency module, which mainly includes the following steps: Step S1, gold ball implantation: Fix the wafer to be processed on the carrier, heat the gold wire with a torch, melt the end of the gold wire to form a ball, then accurately align the gold ball to a specific pad on the wafer, gently press the gold ball on the pad, and apply ultrasonic energy at the same time. The ultrasonic vibration and pressure work together to firmly weld the gold ball to the pad, forming a tiny gold ball solder joint. Once the gold ball is successfully soldered to the pad, the gold wire will be cut off, leaving a complete gold ball solder joint on the pad.

[0027] Ball bonding machines in the prior art generally have the function of planting double balls. In this embodiment, if you want to increase the cavity height of the SAW chip, you can plant double balls, that is, plant two gold balls continuously at the same position, so that the total height of the gold balls is greatly increased.

[0028] Step S2, wafer cutting: In order to protect the wafer surface and the gold balls, a protective layer is usually applied to the wafer surface before dicing. The wafer is cut into individual chips along the predetermined cutting path using a dicing machine. After dicing, the protective layer on the surface is removed to obtain the cut chips.

[0029] Step S3, flip-chip and switch: Use a flip-chip machine to flip-chip the SAW chip and switch onto the PCB substrate of the RF module through the principle of gold-gold bonding.

[0030] Step S4, coating with TSA film: attaching the TSA film to the PCB substrate with the SAW chip and the switch. In this embodiment, the TSA film is a TSA film with a thickness of 50 μm.

[0031] In this embodiment, a thinner epoxy resin film may be used to replace the TSA film. The thickness of the epoxy resin film is 50 μm.

[0032] Step S5, coating with epoxy resin film: attaching a semi-solid epoxy resin film to the surface of the TSA film, and curing the TSA film and the epoxy resin film in an oven. In this embodiment, the curing temperature of the oven is 150°C to 250°C.

[0033] In this embodiment, when an epoxy resin film is used in step S4, an extrusion injection molding process can be performed after the epoxy resin film is cured to form a protective film.

[0034] Step S6, cutting the PCB substrate: cutting and taping the cured PCB along the cutting paths of the PCB to obtain a DiFEM module.

[0035] The present invention mainly simplifies the ball implantation process and SMT process of the RF module, and uses the common ball welding machine, flip chip machine, laminating machine, etc. in the SAW packaging production line to package the RF front-end DiFEM module. The original process is mainly innovated in the following aspects: 1. Use a ball welder to plant gold balls on the wafer instead of using printed solder paste to plant solder balls.

[0036] 2. Replace SMT equipment with existing flip-chip machines.

[0037] Before the improvement, conductive solder balls were mainly made through chemical plating, printing solder paste, reflow, etc. This method requires repeated switching of dry and wet processes, and the process flow is cumbersome and costly. The SMT process requires printing solder paste, making steel mesh, etc.

[0038] After the improvement, it is only necessary to use a ball soldering machine to implant gold balls on the surface of the wafer, which is a simple process; and the flip-chip gold-gold bonding principle replaces the SMT process, and the process principles and methods are innovative to a certain extent.

[0039] The present invention greatly simplifies the process steps of BDMP packaging and improves production efficiency; reduces the material and energy consumption required in production, and also reduces labor and maintenance costs; reduces the probability of process problems, thereby improving the overall quality and consistency of the product.

Claims

1. A novel BDMP packaging method for DiFEM radio frequency module, characterized by: The packaging method comprises the following steps: Step S1, implanting a gold ball: fix the wafer to be processed on a carrier, heat the gold wire with a torch, melt the end of the gold wire to form a ball, then align the gold ball to a specific pad on the wafer, gently press the gold ball on the pad, and apply ultrasonic vibration at the same time. The ultrasonic vibration and pressure work together to weld the gold ball and the pad together to form a tiny gold ball solder joint. The gold ball is soldered to the pad, and the gold wire is cut off, leaving a complete gold ball solder joint on the pad; Step S2, wafer cutting: using a dicing machine to cut the wafer into individual chips along predetermined cutting paths; Step S3, flip-chipping of the chip and the switch: using a flip-chip machine to flip-chip the SAW chip and the switch onto the PCB substrate of the RF module through the principle of gold-gold bonding; Step S4, laminating: attaching the film to the PCB substrate with the SAW chip and the switch; Step S5, coating with a protective film: attaching a protective film to the coating surface in step S4, and curing the protective film; Step S6, cutting the PCB substrate: cutting and taping the cured PCB along the cutting paths of the PCB to obtain a DiFEM module.

2. The novel BDMP packaging method for DiFEM radio frequency module according to claim 1 is characterized in that: In the step S2, a protective layer is applied on the surface of the wafer before the wafer is cut.

3. The novel BDMP packaging method for DiFEM radio frequency module according to claim 2 is characterized in that: In the step S2, the protective layer on the surface of the wafer is removed after the wafer is cut to obtain the cut chips.

4. The novel BDMP packaging method for DiFEM radio frequency module according to claim 1 is characterized in that: In the step S1, when implanting the gold balls, two gold balls are implanted continuously at the same position.

5. The novel BDMP packaging method for DiFEM radio frequency module according to claim 1 is characterized in that: In the step S4, TSA film or epoxy resin film is used for lamination.

6. The novel BDMP packaging method for DiFEM radio frequency module according to claim 5 is characterized in that: The TSA film or epoxy resin film has a thickness of 50 μm.

7. The novel BDMP packaging method for DiFEM radio frequency module according to claim 1 is characterized in that: The protective film is made of epoxy resin film or plastic film.

8. The novel BDMP packaging method for DiFEM radio frequency module according to claim 1 is characterized in that: When the protective film is an epoxy resin film, an oven is used for curing, and the curing temperature of the oven is 150°C to 250°C.