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To understand BGA assembly, we need to know what is BGA first. And BGA assembly means soldering of BGA chips on printed circuit boards. 

In the first half of the 1990s, a second IC packaging technology appeared in America representing surface assembly technology –BGA (ball grid array packaging), and its further small packaging (CSP (chip scale packaging), which became the focus of attention in the late 1990s.

The typical ball grid arrays package (BGA) is very durable and can be assembled once it has been dropped to the floor. This is somewhat impossible for PQFP packaging. The form of the area array characterizes the BGA providing more I/O per area than QFP. The number of I/O can always exceed 250. Under this circumstance, BGA takes up less space than QFP. The course of the BGA assembly is easier to be carried out and thus generates outstanding production efficiency.

If package-related defects are measured before assembly, the assembly efficiency of this area array package can approach less than 1ppm/ line level for the first pass. There is no doubt that the following conditions will happen in the process of the BGA assembly including the loss of balls, the sensitivity of humidity, the damage during the shipping, etc. Under these conditions, package-related defects could be the result. There is a very large variation in ball size, about two to three times the volume difference from ball to ball. Double ball at a spot location and defects associated with metallization such as poor solder between the ball and component pads.
Due to process issues, the strongest manufacturing process for BGA assembly provides the lowest defects. However, the assembly problem is still plaguing the area of the array packaging manufacturing industry. This is not surprising since the normal maturation cycle of BGA packaging has not yet been completed.

Different from the QFP, the BGA package should be carried out with a shorter lead length and better electrical performance is required. Yet the high cost must be taken into consideration as one of the outstanding disadvantages of constructing BGA components. To draw a comparison, there are more expensive raw ingredients contained in BT resin, ceramic, and polyimide resin carriers while QFPs are made of materials like low-cost molded resins and sheet metal lead frames.

Area array carriers are very expensive to produce because of thin wire circuits and chemical treatment processes. In addition, compared with the BGA packaging process, QFPs can use silicon packaging materials, and its process steps require less high-output finishing die and multi-cavity die pressure. Once the high volume is achieved, the cost of area-array packaging will fall, but perhaps not to the QFP cost profile.

So BGA PCB assembly means solder ball grid array components on the surface of a printed circuit board. NOmraly we need high-accuracy pick and palace equipment to put the BGAs on the PCB currently, and then solder the BGAs by running through the SMT reflow oven. And the whole process is BGA assembly process. 

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    Features & Trends of BGA Packaging

    However, when QFP is applied, it is considered that BGA will be justified in terms of economic value only under the following conditions. Below 200I/Os, QFPs are applicable and relatively easy to assemble. But above 200I/Os, the opposite is true. When QFP is not available, this situation will lead to the widespread use of BGA. And most likely a high-lead element, using a BGA package higher than 200I/Os.

    The inspection and repair of BGA circuits becomes increasingly mature. Although inspection of finished products is possible, sophisticated equipment such as X-ray imaging systems or ultrasound microscopy systems is required. As the entire BGA packaging production cycle and experience continue to mature, the statistical sampling inspection will find fewer problems, resulting in a gradual increase in production efficiency.

    Rework is also an issue worth considering. The rework of BGA is mainly due to various defects related to the components, so it is important to complete the good BGA assembly process. Because the connector is located under the package, BGA assembly packages is much more difficult to repair than a connector with a peripheral lead device.

    The issues to be considered for repair include CHIP temperature, the temperature distribution on the component during the repair cycle, and the temperature distribution on the plate. If all the equipment needed is purchased, the cost of BGA components repair will be very expensive.

    A disadvantage of BGA packaging is the inability to properly wash flux waste off the surface of the plate at the bottom of the array package. At present, the size of the top foot number of face array packages is close to 45mm, so the cleaning problem becomes quite critical. The various fluxes and pastes required for cleaning can result in electrical failure and leakage of the grounding code in high-power applications.

    To reduce the problem of residual flux waste at the bottom of the package, the use of no-wash flux/solder paste is required for large-area array packaging applications. Cleaning systems with various solvents can properly clean the bottom of the BGA package, but face various environmental limitations and high-cost problems.

    Several specifications of BGA package types currently available include plastic over-mold BGA (PBGA), organic belt carrier BGA (TBGA), ceramic BGA (CBGA), ceramic cylindrical array (CGA), cavity type BGA, including heat reinforced and chip cavity down type, metal body BGA (MBGA). It is generally believed that TBGA, CGA, and CBGA packages use high melt solder alloy (10Sn/90Pb), while most other BGAs use low melt eutectic solder 63Sn/37Pb or close to low eutectic 62Sn/36Pb/2Ag solder alloy.

    In summary, the larger than 208 pins with 0.5mm spacing that have become common over the past few years are not widely used, nor are the higher pins with 256 pins with 0.4mm spacing and 304 pins with 0.4mm spacing. Most QFPs are plastic and ceramic shell models, and generally, various plastic-type devices are suitable for higher lead numbers. In addition, two less commonly used QFP types are the sealed TAB type and the metal shell type (high heat loss).

    With the increase in the number of QFP package leads, the shell size increases sharply. Instead of increasing the package size, the lead spacing can be further reduced. Some commercially available 0.3mm spacing devices have been successful, but limited packaging effectiveness and very compact assembly processes have prevented large-scale device assembly. Generic QFPs products come from many sources, including IBM, Intel, Shinko, Seiko, Olin, Swire, IPAC, and Motorola.

    BGAs are universal in a wide variety of types above the 200I/O number level. In plastic BGAs, the universal package specifications include 225, 256, 313, 352, 361, and 400I/O number of various components. A variety of thermally enhanced surface array packages include 479 and 503 pin types. Cavity-down type BGAs are currently available in 204, 208, 240, 256, 312, 352, 432, 479, 560, and 596, etc. The types of TBGAs available are 240, 342, 432, 647, and 736 pins and can be fitted with heat sinks or a metal plate attached to the rear back of the package.

    CBGAs are typically used in applications with very high pin counts, over 1000I/O counts. To solve the problem of high heat loss, two kinds of metal shell-type BGAs have been tried in recent years. The suppliers of generic BGAs packaging products mainly include IBM, Motorola, Citizen, LSI Logic, Amkor, Anam, Cassia, SAT, AT&T, National Semiconductor, Olin, and ASE, among others.

    PQFP with less than 200 leads is expected to be the dominant packaging technology for some time to come. When the lead count is higher than 350, QFPs can’t be widely used. Between 200 and 300I/O devices, there will continue to be competition between the two areas of packaging technology. Therefore, the less than 0.5mm QFP packaging process will be replaced by the very attractive BGAs packaging process. However, compared with the more modest 8% annual growth of PQFPs, BGA will increase by 25% annually.

    We consider BGA (ball grid array) as the typical packing style now that the technology of chip packaging gains ground. A BGA chip is a chip with hundreds of pins, and the application of a BGA package brings great advantages.

    In terms of the shape of the BGA package, the BGA chip has more advantages, power performance, and practicability than QFP (square flat package) chip. The BGA package greatly reduces the physical size of the chip. The pins of the BGA chip can directly replace the peripheral leads of the QFP chip, which is especially obvious when multiple I/O pins are used. As the number of I/O pins changes, the area of BGA increases linearly with the increase of the number of I/O pins, while the area of QFP increases with the increase of the number of I/O pins. Thus, the BGA package provides higher manufacturability than QFP for devices with multiple pins.

    In general, I/O pins range from 250 to 1089, depending on package type and size. In terms of manufacturability, BGA chips also outperform QFP chips. The pins of the BGA package chip are spherical and distributed in a 2D array. In addition, I/O pins have greater spacing than QFP and can act as hard balls that do not deform due to contact. For chipmakers, another advantage of BGA chips is their high volume. It should also be noted that the package defect rate of BGA chips is usually 0.3 PPM to 5ppm per pin, which can be regarded as equivalent defect free.

    Based on the above advantages, BGA package chips are widely used by electronic assemblers. However, we need to use some important layout techniques at the design stage for high-speed design, otherwise, the special shape of the BGA package will lead to an increased risk of welding short circuits. Therefore, the following mainly explain some important layout specifications of ball grid array chips, to achieve the best welding effect in the SMT patch processing devices, avoid the phenomenon of short circuits, and improve the yield.

    1. lead bonding PBGA packaging method

    1. Preparation of PBGA substrate

    Before the steps of drilling and through-hole metallization, we should make extremely thin (12 to 18μm thick) copper foils laminated on two sides of the BT resin or glass core plate, with the means of conventional PCB plus 3232 techniques to fabricate graphics on the substrate as regards guide tape, electrodes, and weld zone arrays for mounting solder balls. Particularly, a single substrate composed of several multiple PBG substrates does well in improving production efficiency.

    2. Packaging course

    Wafer thinning → wafer cutting → chip bonding → Plasma cleaning → lead bonding → plasma cleaning → molding packaging → solder ball assembly → reflow soldering → surface marking → separation → final inspection → test bucket packaging

    • In the course of chip bonding, we bond IC chips to the substrate by adding a silver-filled epoxy binder first. Next, gold wire bonding is needed to connect the chip and the substrate. Afterward, the chip, welding wire, and solder pad should be protected by molding encapsulation or liquid glue potting which can ensure they can function well.
    • Finally, balls will be soldered at the high temperature of 183℃ and placed on the pad by a kind of pick-up tool.
    • What’s more, the reflow welding process will be unfolded. After going through a reflow furnace at the maxi temperature of 230℃, the substrate is decoupled by a CFC inorganic cleaner.
    • Thus, the solder and fiber particles can be removed and won’t be left on the package. Then a series of steps including marking, separation, final inspection, testing, and packaging for storage has to be carried out.

    2. Packaging method of FC-CBGA

    1. Ceramic substrate

    As is known to us, the substrate of FC-CBGA, belonging to a multilayer ceramic substrate, really takes time and high cost to make. Just take a glimpse at the following issues: the high wiring density of the substrate, the narrow spacing, the higher requirements of the substrate, etc.
    However, we should note that sometimes the CBGA products may fail to perform well due to the mismatch between the CTE and the substrate, chip, and PCB board. Consequently, we may use another type of ceramic substrate —HITCE ceramic substrate to avoid such failure.

    2. The Packaging steps

    Preparation of wafer bump; Wafer cutting; Chip flip and reflow bonding; Bottom filling thermal grease; protection solder distribution; Block; Assembly solder ball; Reflow bonding; Marking; Separation; Final review check ]; packaging
     


    3. lead bonding TBGA packaging method

    Above all, the polyimide is the core material to fabricate the band carrying TBGA.

    In the manufacturing process, both sides of the band are coated with copper, followed by nickel and gold plating. The next steps are punching and through-hole metallization and fabrication of graphics. Concerning this lead-bonded TBGA, the encapsulated heat sink is the solid added to the package and the carrier band is bonded to the heat sink with a pressure-sensitive adhesive before encapsulation.

    Wafer thinning → wafer cutting → chip bonding → cleaning → lead bonding → plasma cleaning → liquid sealant potting → Solder ball assembly → reflow soldering → surface marking → separation → final inspection → testing → packaging

    There are unit 2 main interconnect modes between chip and substrate in the BGA package structure: lead bonding and reverse bonding. The number of I/ OS of a BGA ranges from 100 to 1000. Cost, performance, and workability are the main considerations when choosing which approach to use. The I/O number of BGA using lead bonding is usually 50~540, and the I/O number of BGA using backloading welding is often & GT; 540.

    In addition, the choice of interconnect mode depends on the physical characteristics of the package substrate material used and the application conditions of the device. PBGA interconnect is commonly used by lead bonding, CBGA is commonly used by backward welding, and TBGA is used in both interconnection modes.

    When the number of I/O & lt; At 600, the cost of lead bonding is lower than that of backloading welding. However, the backloading method is more suitable for mass production, and if the wafer yield is increased, the cost of each device can be reduced. And backward welding can reduce the volume of the package.

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    Advantages of PCB BGA Packaging

    With the increase in the density of programmable devices and the number of I/O pins, the ball grid arrays (BGA) package can interconnect I/O inside the device to improve the number of pins and the area ratio of the circuit board, which is an ideal package scheme. So, what are the advantages of PCB BGA packaging?
    1

    The pin is not easy to be damaged. BGA components pins are sturdy solder balls that are not susceptible to damage during operation.

    2

    The number of pins per unit area is more. The ball is closer to the edge of the package, and the pin spacing of the BGA components for backloading is reduced to 1.0mm, thereby increasing the number of pins.

    3

    Cheaper surface sticking equipment. The BGA package can withstand minor device misalignments during assembly and can be used with less expensive surface mount devices.

    4

    Smaller contacts. BGA packages are generally 20% to 50% smaller than QFP packages and are more suitable for applications requiring high performance and small contacts.

    5

    Integrated circuit rate advantage. BGA package uses a ground plane, ground loop, and power loop in its structure, which has good electrical performance.

    6

    Improve the heat dissipation performance. The core is located in the center of the BGA package, while most of the GND and V CC pins are located in the center of the package so that heat generated by the device can be dispersed to the surrounding environment through the GND and V CC pins.

    How to Ensure Good Soldering in the BGA Assembly?

    1. Preheat the Ball Grid Array (BGA) style circuit boards and chip to remove moisture and bake the BGA in a tray package at 120℃ for 4 to 6 hours before soldering.

    2. Clean the pads and clean off the flux and solder paste left on the PCB surface.
    3. Fresh auxiliary materials must be used when solder paste and flux are applied. And the solder paste must be stirred well. The solder paste viscosity and the amount of solder paste applied must be appropriate.

    4. Each solder ball on the BGA components must be aligned with each corresponding solder joint on the PCB when mounting components in BGA assembly process. To ensure good quality of BGA assembly board.

    5. In the BGA soldering process, the heating temperature and time of each zone should be correctly selected, and attention should be paid to the speed of temperature rise. In general, before the temperature reaches 100 ℃, the maximum heating speed does not exceed 6 ℃ / s. After the temperature reaches 100 ℃, the maximum heating speed does not exceed 3 ℃ / s. In the cooling zone, the maximum cooling speed does not exceed 6 ℃ / s. Because too fast heating and cooling speed may damage the PCB and chip. This damage is sometimes not observable to the naked eye. At the same time, for different chips and different kinds of solder paste, we should choose a different heating temperature and time.

    6. When designing the PCB, the pads of all the solder joints of the BGA on the PCB should be designed to be the same size. If some through-holes must be designed under the pads, the appropriate PCB manufacturer should be found to ensure that the size of all pads is the same and the amount of the solder paste on the pads is the same and the height is the same. So the PCB designer should check the details in BGA datasheet in advance. 

    7. To ensure the soldering quality in BGA PCB assembly, more and more manufacturers are choosing to inspect components with hidden solder joints by the way of X-ray inspection.

    How to Check Solder Joint Quality in a BGA?

    To check the quality of solder joints in a BGA PCB assembly, we need to observe the geometry of the solder joint, and then check mainly the brightness and luster of the solder joint with the help of X-ray inspection. Moreover, the appearance characteristics of a typical solder joint are described below.
    1. The shape is centered on the welded wire and is drawn evenly and in a skirt shape.
    2. The joint surface of the brazing material looks like semi-bowed concave, the junction of the brazing material and the solder is smooth, and the contact angle is as small as possible.
    3. The amount of solder paste is moderate, and the surface is shiny and smooth.

    4. No cracks, pinholes, slag, pulling tips, floating welding, or other welding defects during BGA assembly process.

    In short, a good solder joint should be bright and smooth. The filler metal layer should be applied evenly with a thin coating. The coating ratio of the filler metal layer matches the size of the pads. The solder joint is in a skirt shape without cracks, pinholes, or flux residue.

    The Benefits and Applications of the BGA Assembly Benefits:

    1. It improves the finishing rate of mounting and potentially reduces the cost.
    2. The contact surface between the solder balls of BGA and the substrate is large and short, which is conducive to heat dissipation.
    3. The pins of BGA array solder balls are short, which shortens the signal transmission path and reduces the inductance and resistance of the lead wire, thus improving the performance of the circuit.

    4. It improves the coplanarity of the I/O side, which greatly reduces the loss caused by poor coplanarity during the BGA assembly process.

    5. BGA circuits is suitable for the MCM package and can realize high density and high performance of MCM.

    6. BGA assembly board is more robust and reliable than ICs in foot-shaped packages with a detailed pitch.

    Applications:

    BGA PCB assemblies are increasingly accepted in a wide range of applications due to their excellent heat dissipation, electrical characteristics, and compatibility with high-efficiency system products, and the majority of BGA packages are used in high-end consumer markets such as cell phones, networks, and communication devices, digital cameras, microcomputers, notebook computers, PADs, and various flat panel displays.

    Why Go for Viasion?

    If you are struggling to find the right BGA assembly supplier, you can choose to trust Viasion as your trusted BGA (Ball Grid Array) Assembly Manufacturer. For 16 years, we have successfully handled different types of BGA assembly, and as a result, we are recognized by our customers as one of the best and most reliable ball grid array assembly suppliers. There is no doubt that we will serve you most efficiently. Our professional BGA assembly services will ensure that your boards will perform at their best in the various appliances in use. In addition, to provide you with a high-quality service to the best of our ability, we perform various tests and a series of inspections to prevent any problems with the assembled boards. Of course, checking the BGA assembly for leaks and cracks after BGA assembly process is also an important part, and our experts take this extremely seriously.

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    Frequently Asked Questions

    BGA, also known as Ball Grid Array, is a high-density surface-mount packaging technology. At the bottom of the package, the pins are ball-shaped and arranged in a lattice-like pattern, which explains its name.
    The BGA assembly process is the same as SMT assembly, firstly apply solder paste on the BGA pads, then place the BGA chips on the PCB board surface, and lastly run through reflow oven to stabilize the BGA chips.
    The normal types of BGA components are CBGA (Ceramic Ball Grid Array), PBGA (Plastic Ball Grid Array) and TBGA (Tape Ball Grid Array).
    BGA is the right package for the devices like the packaging of the chipset for motherboard control, PC chip sets, microprocessors/controllers, ASIC, gate arrays, memories, DSP, PDA, PLD, etc.
    The normal solder ball pitch sizes of the BGA components range from 0.5 mm to 1.0 mm, but can be as small as 0.3 mm.