Introduction of Plastic Ball Grid Array-PBGA
PBGA or Plastic Ball Grid Array packaging is used to provide the high-level PCB assembly process and design at reasonable prices. It is the main type of BGA that is commonly used for double-side PCB construction. The first time it was created by MOTOROLA company and now almost every PCBA manufacturer is using this material in products. Its substrate material is created through bismaleimide triazine. Through the use of this advanced IC packaging technology, engineers can optimize innovations by enhancing the working operation features of semiconductors components.
These packagings are created for low inductance, well SMT assembly technique, and improved thermal operation. These techniques come with ground and power plans that are demanded by advanced electronics. This packaging provides a flexible design structure since uses industry-proven semiconductors grade materials. PBGA helps to mount components permanently like microprocessors. This packaging provides a larger number of pinouts that helps to make a connection with dual in-line or flat packaging. Its structure is such that we can use its complete lower area instead of only the perimeter.
Features of PBGAs
Due to the continuous improvement of IC chip functions and clock speeds, Chinese PCBA manufacturers are really looking for efficient ways to assemble them. After trying more new ways, plastic ball grid array (PBGA) technology stands out, it is considered to be the first choice for high I/O devices and less pins applications, customers make projects more profitable through this BGA assembly. Drivers include the density advantage of area arrays, rapid Six Sigma assembly yields with existing assembly equipment, the potential for excellent electrical and thermal performance, and the traditional low cost of plastic packaging. Next, we will describe the characteristics of plastic ball grid arrays:
- Some major characteristics of PFBA are explained here
- There are 1521 customs ball counts for this packaging.
- Normally standard ball pitch is 1.00 mm, 1.27 mm, and 1.50 mm but for some high-level projects other values can be created.
- Normal dimensions of the packaging are about 17 mm to 40 mm.
- It is more compatible with copper and gold than wire.
- It comes in a chip-on-chip structure.
- There is a larger mod cap exit to provide the high quality.
- It is low-weight packaging.
- It provides good thermal and electrical.
- Through the use of this technology, HDI design can create.
- It is the best substrate for MCM and integrated SMT designs.
- It is compatible with Automotive AEC-Q100.
- 63 Sn/37 Pb or lead-free solder balls used.
- It provides highly reliable operations.
- It can have 2-layer or 4-layer substrates.
- Mature strip-based manufacturing process with high yields.
SMD and NSMD PCB Pads for PBGA
There are two types of PCB pads used for plastic ball grid arrays. One is Solder Mask Defined Land (SMD) and the other is Non-Solder Mask Defined Land (NSMD). At the industrial level, copper-defined pads are mostly used in PCBA boards. Next we will compare the advantages and disadvantages of SMD components and NSMD in PBGA assembly.
SMD advantages and disadvantages
Electronic manufacturers use SMD components because it can provide better mechanical strength and make the assembled PCBA board more heat-resistant. This technique uses larger copper and spread heat in the proper way all over board.
While SMD is an excellent assembly strategy, when soldering for SMT assembly, foreign objects may appear on the pads and there are potential pressure points on the circuit board. Possibly worse dimensional tolerance on solderable diameter versus NSMD.
NSMD advantages and disadvantages
This is a commonly used pad type, which makes soldering more selective. It has high copper to copper trace to route traces among pads. It does not have any point of stress concentration on the board.
It reduces pad-to-PCB adhesion strength. There may be a weak link in another mechanical device testing, i.e. board beding, mechanical shock, and vibration. Unsymmetrical joint fails in package interface first in term cycling.
PCB Pad Design Parameters
PCB Pad Dimensions
- The diameter of the solderable pad must be equal to packaging dia
- The dia of small size PCB board pad is about ten percent can help for easy routing and also have good reliability
- For NSMD pad soldering opening parameter must be 0.125 mm > pad diameter
- SMD pads must be 0.125 mm > solder mask opening
- For PCB surface finishing use OSP, HASl, immersion silver, or electroless
Solder Paste Printing for PBGA
The solder paste stencil thickness for PBGA has values of 0.10 to 0.20mm. The thickness of the stencil is normally defined by other components existing on the board like good pitch leaded and small components. There is no minimum value for solder paste volume for PBGA as solder material completely melted and diminish during the reflow process.
To get good gasketing apertures must be the same as the PCB pad diameter. In some situations like larger size PBGA thick stencil can provide well assembly robustness ± 0.025 mm solder paste print to PCB board is commonly used and past must not touch any surrounding exposed metallization.
PCB Routing Vias
For pitches of 1.27, 1.0, and 0.8 mm, through the interstitial between BGA pads
- Via Cu retaining pad adjusted according to the size of the via drill
- The capture pad is usually provided with a solder mask
- The trace between the pad and the capture pad must be covered through a solder mask the smaller layer of solder mask can cause the solder mask to lift from the trace
- For pitches of 0.8, 0.65, and 0.50 mm, via-in-pad construction
- Via is configured with the BGA pad
- Via must bed filled completely to minimize voids in the final solder joint
Considering Plastic Ball Grid Array Assembly?
Advantages of PBGA Assembly
This technique is the finest option to make miniature packaging for ICs that have a larger number of pinouts. In the older technique pin grid array and dual inline surface, mount packaging also had more pins and fewer areas among the pins but it was very difficult to solder these pins. When packaging pins are positioned close to each other the result of their PCB short circuit increases.
Its other benefit is that low thermal resistance among packaging and board than other packaging having discrete leads. Their structure is such configured that heat produced through ICs in packaging moves easily to the board that helps the chip to save from overheating.
Small electrical conductors cause less undesired inductance, it is an advantageous PBGA technique since in high-speed signal circuits that feature causes undesired distortion for signal. PBGA some with a small distance between packaging and board and also have less value of lead inductances that results in high electrical operation to pinned devices.
Disadvantages of PBGA Assembly
The disadvantage of BGA is that the solder balls cannot bend the way longer wires can, so they are not mechanically compatible. In the case of SMD components bending due to the difference in thermal expansion coefficient among PCB substrate and PBGA or flexing and mechanical stress results in fracture of solder joints. Thermal expansion issues can be decreased by relating the mechanical and thermal features of the board with the packaging. Normally PBGA devices match their thermal features more than ceramic components.
The other drawback of this technology is that when you soldered the packaging then it is not easy to find faults existing in the packaging. To resolve this issue X-RAY machines, Industrial CT scan machines, and microscopes are used. If the soldering of PBGA is not good, it can be removed at the rework station which is a fixture equipped with an infrared lamp, a thermocouple, and a vacuum device to lift the package. PBGA will be changed or recreated and then positioned on the PCB board. Already mad solder balls same to an array pattern can connect to repackage BGAs when only one or a few need to be reworked.
When PCB manufacturing is in progress it is not good to solder BGA into the structure and sockets can be used in place of it which looks like an unreliable technique. Two main types of sockets but the reliable type has spring-loaded pins that push up under the balls though it does not help PBGA to use without balls since spring-loaded pins are small. The less reliable socket is ZIF which has spring pinchers that grab balls. It does not properly operate especially for small balls.
The instrument used for Plastic Ball Grid packaging is expensive and hand-soldering PBGA packing is very difficult and unreliable and used for small packaging. However, as more and more integrated circuits became available only in lead free PCB assembly or PBGA, various proprietary reflow methods were developed using less costly heat sources like heat guns, home toasters, and electric pans.
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