BGA process has become one of the best choices for IC packaging. Up to now, more and more kinds of BGA packaging technology, different kinds have different characteristics, and the process flow is not the same. At the same time, with the development of BGA technology and the IC industry, domestic sealing test manufacturers gradually stepped onto the historical stage.
In the 1990s, BGA (Ball Grid Array, Ball grid array, or solder Ball array) packaging technology developed rapidly and became one of the mainstream packaging technology. It is a high-density surface assembly package technology, at the bottom of the package, the pins are spherical and arranged in a lattice-like pattern, hence the name BGA.
At present, the main board control chipset mostly adopts such packaging technology, and the material is mostly ceramic. Using BGA technology to package the memory, the memory capacity can be increased by two to three times without changing the size of the memory.
The main contents of this paper are the main classification and characteristics of BGA packaging, the BGA packaging process, and domestic sealing and testing manufacturers.
BGA packaging technology classification and characteristics
There are many packaging types of BGA, which can be divided into peripheral type, staggered type, and full array type according to the arrangement of solder balls.
According to the different substrates, it is mainly divided into PBGA (Plastic BGA), CBGA (Ceramic BGA), FCBGA (Filpchip BGA, flip BGA), and TBGA (Tape BGA, carrying BGA).
PBGA is the most common form of BGA packaging, made of plastic materials and plastic processes. The substrate type used is PCB substrate material (BT resin/glass laminate). After the bare chip is connected to the top of the substrate and the pin frame by bonding and WB technology, the overall plastic mold is achieved by injection molding (epoxy film plastic mixture). Intel series CPUs use this encapsulation mode for Pentium II, III, and IV CPUs.
The ball material is a low melting point eutectic alloy 63Sn37Pb, with a diameter of about 1mm and a spacing range of 1.27-2.54mm. No additional solder is required for the connection between the ball and the bottom of the package. When assembled, the ball melts and joins together with the PCB surface, presenting a barrel shape.
PBGA packaging features are mainly shown in the following four aspects:
- Low production cost, cost-effective.
- The ball participates in the formation of a reflow welding spot, and the coplanar degree is required to be loose.
- Good thermal matching with epoxy resin substrate, high quality, and good performance when assembling to PCB.
- Sensitive to moisture, the PoPCorn effect is serious, causing potential reliability problems, and the high QFP of packaging height is also a technical challenge.
CBGA is formed by installing the bare chip on the top surface of the ceramic multilayer substrate carrier. The metal cover plate is welded on the substrate with sealed solder to protect the chip, lead, and pad. The connected package body is treated with air tightness to improve its reliability and physical protection performance. The Pentium I, II, and Pentium Pro processors have all been packaged in this way.
CBGA uses a multilayer ceramic wiring substrate, and the solder ball material is eutectic solder with a high melting point of 90Pb10Sn. The connection between the solder ball and the package body uses low-temperature eutectic solder 63Sn37Pb and adopts a cover + glass gas seal, which belongs to the category of gas-tight packaging.
CBGA packaging features are mainly shown in the following six aspects:
- Not sensitive to moisture, good reliability, and excellent electrical and thermal performance.
- Good matching with the CTE of the ceramic substrate.
- Good repairability of connected chips and components.
- The bare chip adopts THE FCB technology to achieve higher interconnection density.
- High packaging cost.
- Poor matching with epoxy resin substrate CTE.
FCBGA is currently the most important packaging format for graphics acceleration chips. This packaging technology began in the 1960s when IBM developed the so-called Controlled Collapse Chip Connection (C4) technology for the assembly of large computers. Subsequently, the surface tension of the molten bump can be used to support the weight of the chip and control the height of the bump, and become the development direction of flip technology.
The package uses a ball instead of a needle to connect the processor. A total of 479 balls, each 0.78mm in diameter, are required to provide the shortest external connection distance. FCBGA is connected to the substrate through FCB technology. The difference between FCBGA and PBGA is that the bare chip faces down.
FCBGA packaging features are mainly shown in the following three aspects:
- Excellent electrical performance, at the same time, can reduce the component interconnection loss and inductance, reduce the electromagnetic interference problem, and withstand high frequency.
- Improve I/O density, improve efficiency, and effectively reduce the substrate area by 30% to 60%.
- Good heat dissipation can improve the stability of the chip at high speed.
TBGA, also known as array load automatic bonding, is a relatively new FORM of BGA packaging. The substrate type used is PI multilayer wiring substrate, solder ball material is high melting point solder alloy, welding using low melting point solder alloy.
TBGA packaging features are mainly shown in the following five aspects:
- Good thermal matching with epoxy PCB substrate.
- The thinnest BGA package form is conducive to chip thinness.
- Compared with CBGA, the cost is lower.
- More sensitive to heat and humidity.
- The chip is light and small and has a large self-calibration deviation compared with other BGA types.
BGA packaging process
At present, many chip packages are BGA type, the biggest advantage of this type of package is to save space on the board. The most common is the upward structure of the chip, the high heat treatment requirements of the smooth are the use of the cavity downward structure.
Most packages use chip bonding technology to connect the chip and the substrate and realize the electrical connection between the chip and the substrate. BGA is the same, but with more flip-chip interconnect technology. The flip-chip design can connect the heat sink directly with the chip to achieve better heat dissipation.
➡️PBGA packaging process
a. Preparation of PBGA substrate
In BT resin/glass core plate on both sides of the pressure very thin (12-18um thick) copper foil, and then drilling and through the hole metallization, through the hole is generally located around the substrate; The graphics (guide band, electrode and solder zone array for ball mounting) are then fabricated on both sides of the substrate using conventional PWB processes (pressure film, exposure, development, etching, etc.); Finally, the formation of dielectric resistance welding film and graphics, exposed electrode and welding area.
b. Packaging Process
Wafer thinning → Wafer cutting → chip bonding → cleaning → lead bonding → cleaning → molding packaging → solder ball assembly → reflow soldering → marking → separation → inspection and testing → packaging
Chip bonding: Silver-filled epoxy resin binder (conductive adhesive) is used to bond the IC chip to the substrate coated with Ni-Au thin layer
Lead bonding: after bonding and curing, the welding area on the IC chip and the ni-Au plating welding area on the substrate are connected by gold wire with a gold wire ball welder
Molded package: epoxy resin molded with quartz powder to protect the chip, welding line, and pad.
Reflow soldering: After curing, a solder ball Sn62Pb36Ag2 or Sn63Pb37 with a melting point of 183℃ and a diameter of 30mil (0.75mm) is placed on the pad using a specially designed pickup tool (automatic ball pickup). Reflow welding is carried out in a conventional reflow furnace in an N2 atmosphere (maximum working temperature does not exceed 230℃), and the balls are welded to the ni-Au plated substrate welding zone.
➡️TBGA Packaging Process
a. TBGA tape production
TBGA carrier tape is made of polyimide PI material. During production, copper is first covered on both sides of the carrier tape, and then through holes are punched and metalized and graphics are made. Then nickel and gold are plated, and the carrier bands with metalized through holes and redistribution patterns are divided into monomers.
The packaging heat sink is also packaging solid and is also the core cavity base of the shell, so before packaging, the pressure-sensitive binder should be used to bond the carrier to the heat sink.
TBGA is a package for high I/O applications with I/O numbers ranging from 200 to 1000. The chip connection can be refluxed by flip-chip or hot-pressed bonding.
b. TBGA Packaging Process
Wafer thinning → wafer cutting → chip bonding → cleaning → lead bonding → plasma cleaning → liquid sealant filling → solder ball assembly → reflow soldering → marking → final inspection → test → packaging
Chip bonding: full array chip, using C4 process; Peripheral type gold bump chip, hot pressing bonding.
Assembly solder ball: micro-welding technology welding ball (10Sn90Pb) to the load belt, the top of the ball into the electroplating through-hole, after welding with epoxy resin chip encapsulation.
➡️FCBGA Packaging Process
a. FCBGA substrate production
FCGBA substrate production is the multi-layer ceramic sheet high temperature co-firing multi-layer ceramic metalized substrate, and then making multi-layer metal wiring on the substrate, and then electroplating, etc.
b. FCBGA Packaging Process
Wafer convex preparation → wafer cutting → chip flip and reflow soldering → bottom filling → distribution of thermal grease and sealing solder → capping → solder ball assembly → reflow soldering → marking → separation final inspection → test → encapsulation
Flip welding: it overcomes the limit of center distance of lead bonding pad, provides more convenience in the design of power supply/ground wire distribution, and provides a more perfect signal for high-frequency, high-power devices.
Substrate selection: the key factors are the coefficient of thermal expansion (CTE), dielectric constant, dielectric loss, resistivity, and thermal conductivity of the material.
Bump technology: commonly used bump material is a gold bump, 95Pb5Sn, 90Pb10Sn solder ball (reflow welding temperature is about 350℃). The trick is to keep the size of the bump constant as the pitch shrinks. The consistency and coplanar of solder bump size have a great influence on the pass rate of reverse welding.
➡️CBGA Packaging Process
Compared with PBGA and TBGA, CBGA is slightly different in three aspects:
- CBGA substrate is a multilayer ceramic substrate, PBGA substrate is BT multilayer wiring substrate, and TBGA substrate is a polyimide (PI) multilayer Cu wiring substrate.
- The balls below the CBGA substrate are 90%Pb-10Sn% or 95% PB-5Sn % high-temperature balls, while the solder for welding with the substrate and PWB is 37%Pb-63Sn% eutectic low-temperature balls
- The cover of CBGA is ceramic, making it an air-tight package; PBGA and TBGA are plastic packaging, non-airtight packaging.