The spread of 5th generation mobile communication systems (5G) has led to semiconductor devices becoming smaller and more integrated, and has also increased demand for product inspection and analysis.
This section introduces examples of observation and measurement of the bumps of BGAs, which are common observation targets for digital microscopes.
- Typical IC Packages
- Typical Bonding for IC Chip Mounting
- Bump Making Methods for Flip-chip Bonding
- Examples of Observation and Measurement of BGAs (Bumps) Using a Digital Microscope
As ICs become more integrated ICs, surface mount technology (SMT) has become mainstream. Matrix type (BGA
type) packages are used for highly integrated ICs.
This section introduces the following typical IC packages.
These are SMT packages with no leads. Electrode pads are used as connection terminals. SON are two-way type packages used for small numbers of pins.
QFN (quad flat no-leaded) packageThese are SMT packages with no leads. Electrode pads are used as connection terminals. QFN are four-way type packages.
Solder balls (sphere shaped) are arrayed on the bottom of the package to use as terminals.
PGA (pin grid array)Pins are arrayed on the bottom of the package to use as terminals.
LGA (land grid array)Electrode pads (incl. copper pads) are arrayed on the bottom of the package to use as terminals.
Wire bonding is used to connect semiconductor chip electrodes to the electric conductors of lead frames or boards with thin wires of gold, aluminum, or copper.
The method where IC chips are attached directly to a PCB is called FC-BGA (Flip Chip-BGA). Bumps are made on the electrodes of an IC chip and then connected to the electrodes of a PCB. This saves space, compared to wire bonding.
- Left: IC chip
- Right: Flip (face down)
The latest examples of observation and measurement images of BGAs (bumps) using KEYENCE’s VHX Series 4K Digital Microscope are introduced below.
Tilted observation of BGA bumps
100×, ring illumination
Tilted observation allows observation of BGA balls through a clearance on a PCB.
3D measurement of BGA bumps300×, mixed illumination (glare removal image)
Mixed illumination and the glare removal function allow for observation without glare.
Cross-section observation of BGA bumps
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BGA, short for ball grid array, contains arrays of tin balls arranged in grid and its solder balls play a role as connection interface between packaging ICs and PCBs. Their connection is acquired through the application of SMT (surface mount technology). The definition of BGA has been released for almost 10 years and BGA package will be accepted by increasingly wider application fields due to its excellent thermal dissipation capability, electrical property and its compatibility with high-efficiency system products as a result of its high number of pins, which is actually inevitable.
BGA packages have developed into different classifications after upgrading and research carried out by numerous companies. This article will bring forward a brief introduction of their overall categories in the remaining section, which will be a designer-friendly reference as optimal BGA is considered being picked up for perfect balance between performance and cost.
• PBGA
PBGA, short for plastic ball grid array, was invented by Motorola and now has received the widest focus and applications. With BT (bismaleimide triazine) resin used as substrate material, together with the application of sealant technologies of OMPAC (over molded pad array carrier) or GTPAC (glob to pad array carrier), the reliability of PBGA has been verified by JEDEC Level-3. Up to now, PBGA packages containing 200 to 500 solder balls are widely applied, working best for double-side PCBs.
Image Cited from electronics COOLING
• CBGA
As is its name defined, CBGA (ceramic ball grid array) packages take advantage of ceramic as substrate material and tin balls (ratio between tin and lead: 10:90) with high melting point. Internal chip depends on C4 (Controlled Collapse Chip Connection) for perfect connection between BGA and PCB. This type of connection features excellent thermal conductivity and electrical performance. Furthermore, CBGA holds excellent reliability but with high cost. Therefore, CBGA packages are more suitable for automotives or high efficiency chips.
Image Cited from Test and Measurement World
• TBGA
TBGA, short for tape ball grid array, is capable of effectively shrinking package thickness and providing excellent electrical performance. Moreover, excellent thermal dissipation effect can be obtained when heat sink and chip face down design are applied. Thus, TBGA works suitably for high-efficiency products with thin packages. For chips facing down, flip chip technology should be selected while for chips facing up, wire bond should be selected. Generally speaking, TBGA features higher cost than PBGA.
Image Cited from Test and Measurement World
• EBGA
EBGA (thermal enhanced ball grid array) is another form of PBGA with the only difference in terms of structure that is heat sink is added. Chip is directly stuck to heat sink with face down and the electrical connection between chip and PCB is achieved in wire bond. Its sealant method goes like this: dam is built on substrate that is around chip and then liquid compound is used. The cited image below is a good sample of EBGA.
Image Cited from Practical components
• FC-BGA
FC-BGA is short for flip chip ball grid array. Similar with CBGA in terms of structure but with BT resin used to replace ceramic substrate, FC-BGA saves more cost. Moreover, flip chip is capable of shortening internal circuit pathways, effectively improving electrical performance. Material used by metal bump leveraged by flip chip most takes advantage of tin and lead ratio that is 63:37 so that this type of material will perform large surface tension in melting state. As a result, chips can be pulled to the correction positions without the application of accurate flip chip alignment machine.
Image Cited from Shipco Circuits
• MBGA
MBGA, short for metal ball grid array, is developed by Olin with metal ceramic applied as substrate. Circuits on substrate are manufactured through sputtering coating with chip side facing down and wire bonding as internal connection. MBGA can also provide excellent electrical performance and thermal dissipation effect.
• Micro BGA
Micro BGA is a type of package form with equivalent size with chips, developed by Tessera. Micro BGA performs with chip side facing down and with packaging tape as substrate. A layer of elastomer is carried between chip and tape to release the stress caused by thermal expansion. Connection between tape and chip takes advantage of special silver pins with gold plated on while connection between main board and external environment is achieved through BGA. The essential advantage of micro BGA lies in its miniaturization and light weight that lead to its wide applications in products limited by space. Moreover, it works suitably for storage products with a low number of pins.
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Helpful Resources
• Four Steps to Know BGA
• An Introduction of BGA Packaging Technology
•
Factors Affecting the Quality of BGA Assembly
• Requirements on Design Files to Ensure Efficient BGA Assembly
• How to Get Precise Quote for Your BGA Assembly Demands