SMT (surface mount technology) is presented relative to traditional THT (through hole technology). Compared with THT assembly, SMT assembly saves space by 60% to 70% and reduces weight by 70% to 80% because it makes electronic components directly soldered onto both sides of PCB (printed circuit board) without the need of drilling. Thus, SMT assembly plays a significant role in accelerating miniaturization, light weight and thinness of electronic products, which especially derives from fine pitch SMT (pitch is less than 0.65mm). The development trend mentioned above can be clearly captured by cell phone, PC and video cameras. SMDs (surface mount devices) are a type of components with no leads or short leads such as SOP (small outline package), LCC (leadless chip carrier), PLCC (plastic leadless chip carrier), SOJ (small outline j-lead) package, SOIC (small outline integrated circuit) and QFP (quad flat package) among which QFP accounts for majority of applications.
With the development of IC (integrated circuit), however, it is striving for increasingly more functions and I/O pins. Plus, people stick to increasingly higher requirement of electronic products in terms of miniaturization. Therefore, the application of traditional SMT packaging technology doesn’t work any longer such as by using QFP technology, improving I/O pins and reducing pitch. Leads of QFP are linearly distributed and the lead pitch reduction has already come close to a limit. With I/O pin number constantly increasing, it’s not an easy task to maintain electronic products improving functionally and decreasing volume and to make them electronically reasonable and effective. To solve this issue, another type of package, that is, BGA (ball grid array) packaging technology, is capable of getting the issue successfully solved and has won breakthroughs in manufacturing and application.
Comparison between BGA Packaging Technology and Traditional SMT/SMD
Comparison between BGA packaging technology and traditional SMT/SMD can be implemented from the following perspectives.
• Comparison on Lead Structure
Comparison between BGA packaging technology and traditional SMT/SMD in terms of lead structure can be summarized into the following table.
| Items | Gull wing | J lead | I lead | BGA |
| Capability to adapt multi-lead package | Good | Ordinary | Ordinary | Excellent |
| Package thickness | Good | Ordinary | Ordinary | Excellent |
| Lead rigidity | Ordinary | Good | Ordinary | Excellent |
| Capability to adapt multi-soldering | Excellent | Ordinary | Ordinary | Ordinary |
| Self-alignment capability in reflow soldering | Good | Ordinary | Ordinary | Excellent |
| Capability to be inspected after soldering | Ordinary | Good | Ordinary | Ordinary |
| Cleaning difficulty | Ordinary | Good | Excellent | Ordinary |
| Effective area utilization | Ordinary | Good | Ordinary | Excellent |
• Comparison on Package Size
Three types of packages are used as comparison examples with their parameters displayed in Table 2 below.
| Package | Lead Count | Pitch(mm) | Package Size(mm) |
| BGA | 625 | 1.27 | 32*32 |
| TAB | 608 | 0.25 | 44*49 |
| PQFP | 304 | 0.5 | 46*46 |
Based on the parameter comparison indicated in the above table, it’s obvious that BGA features the largest number of leads and the smallest package size.
• Assembly Density Comparison between All Types of Package Structures
Assembly density comparison between all types of package structures is summarized into Table 3 below.
| Package | Pitch (mm) | Size (mm) | I/O Pin Count |
| BGA | 1.27 | 32.5*32.5 | 625 |
| FPD | 0.50 | 32.5*32.5 | 240 |
| UFPD | 0.40 | 32.5*32.5 | 296 |
| UFPD | 0.30 | 32.5*32.5 | 408 |
| TCP | 0.25 | 32.5*32.5 | 480 |
| TCP | 0.20 | 32.5*32.5 | 600 |
• Assembly Procedure
BGA packaging technology makes traditional SMT package expand with advantages of SMT strengthened. As far as fine pitch components or BGA package components are concerned, they share similar assembly procedures that are depicted by the following figure.
• Assembly Defect Rate
When it comes to assembly defect rate of BGA and QFP, more than 10 years’ assembly experience accumulated along PCBHERO’s manufacturing line, it can be concluded that BGA features lower defect rate and better manufacturability than QFP.
• Final Inspection
Compared with BGA solder paste inspection, fine pitch QFP brings forward added cost due to its reliability inspection. In accordance with characteristics of defects, an automatic system inspecting short circuits or open circuits should be generally applied, which adds the manufacturing of QFP. Because BGA packages feature high manufacturing efficiency and low defect rate, their inspection only centers on alignment and positioning.
• Rework
Rework cost of BGA packages is much higher than that of QFP due to the following reasons:
a. Because it’s almost impossible to carry out modifications to defeat single short circuit or open circuit, all the assembly defects elimination concerning BGA packages have to depend on rework.
b. BGA package rework is more difficult than that of QFP and rework perhaps calls for more equipment and higher cost adding.
c. BGA components after rework always don’t work while some QFP components can still be applied as long as they are carefully disassembled.
When it comes to comparison between BGA and traditional SMT in terms of rework technology, it can be concluded that BGA package rework has to be done with total complete preheating implemented. BGA components share similar preheating temperature with other types of SMDs but call for different preheating temperature rise speed. BGA components need to be gradually heated with a smooth preheating curve.
Furthermore, all the solder balls under BGA packages have to be simultaneously heated. Solder paste for BGA packages has to be strictly applied and modifications are not allowed to be carried out on solder joints. Plus, BGA package components can be conveniently applied owing to their large pitch.
• Reserved Soldering Positions
The leading difference between BGA and QFP in terms of reserved soldering positions lies in that between hidden array and hidden leads. In terms of PCB design capability enhancement, all kinds of packages feature their own advantages but the most fundamental issue lies in tracing density, tracing activity and comprehensive performance.
Because BGA packages feature good thermal dissipation performance, even if PCB design file regulates small spacing between thermal components, BGA packages can provide operating environment with good thermal dissipation capability.
• Soldering Joint Reliability
Soldering joint reliability and assembly rate are influenced by four elements: board solderability, component soldering performance, component coplanarity and solder paste volume, all of which determine final products’ quality.
As a type of new microelectronic packaging technology, BGA will definitely replace QFP to be compatible with new requirement of multiple functions and high I/O pin count.
PCBHERO Specializing in BGA and Other Types of SMD Assembly
As a professional PCB assembler with more than 10 years' experience, PCBHERO is capable of dealing with electronic component assembly with different types of packages including BGA, QFN, QFP, CSP, WLCSP etc. SMDs that can be assembled in PCBHERO workshop start from 01005 and minimum pitch of BGA can be 0.4mm while that of WLCSP 0.35mm to be compatible with miniaturization trend of modern electronics. Feel free to reach us for more details about our Advanced PCB Assembly service. Quotation is always free and welcomed!