BGA and QFN packages
BGA and QFN packages are surface-mount IC packages whose solder joints sit underneath the component body. A BGA (ball grid array) connects through an array of solder balls on its underside, while a QFN (quad flat no-leads) has flat pads along its edges and usually a large exposed thermal pad, so joints cannot be fully inspected visually.
BGA and QFN packages explained
A BGA replaces the leads of older packages with a grid of solder balls on the bottom of the package. This allows many connections in a small area and short electrical paths, which suits processors, FPGAs and memory. During reflow, the balls melt and form joints with the pads on the PCB. Escape routing from the inner rows of a BGA often requires extra layers, via-in-pad or HDI microvias, depending on pitch and ball count.
A QFN is a leadless package: its terminations are flat pads on the edge of the underside, and most QFNs have a large exposed pad in the centre that is soldered to the PCB for heat dissipation and grounding. QFNs are small, thin and have good thermal and electrical performance, which makes them common for power ICs, RF parts and microcontrollers. DFN packages follow the same principle with terminals on two sides only.
Both package types are assembled by reflow soldering with printed solder paste. For QFNs, the stencil aperture on the thermal pad is usually divided into several smaller openings to control solder volume, which limits voiding and stops the package floating. Vias in the thermal pad are often used for heat transfer and need to be tented, plugged or filled to avoid solder wicking away.
Because their joints are hidden, both packages are inspected with X-ray inspection. AOI can check placement and the visible edge fillets of a QFN, but cannot see BGA balls or the thermal pad joint. Moisture sensitivity also matters: many of these packages must be stored dry and baked before reflow if exposed too long.
When BGA and QFN packages matter
BGA and QFN packages matter as soon as a design uses them, because they affect the stack-up, routing, stencil design and inspection plan. Pitch and ball count determine whether standard through-hole vias are enough for fan-out or whether via-in-pad or microvias are needed, which affects the bare board cost.
Typical defects include voids in BGA joints and under QFN thermal pads, head-in-pillow joints where a ball does not fully merge with the paste, bridging between balls or pads, open joints caused by board or package warpage, and insufficient solder on QFN edge terminals. Excessive voiding under a thermal pad reduces heat dissipation.
Rework is more difficult than for leaded packages. Removing and replacing a BGA requires a rework station: the part is removed, the pads are cleaned and a new or reballed component is fitted — reballing is only needed when a removed BGA is to be reused. QFNs need careful heating and new paste. Design choices such as solder mask defined versus non-solder mask defined pads, thermal pad vias and the copper balance around the package all influence yield.
BGA vs QFN vs QFP
QFPs are the most forgiving to assemble and inspect but take more board area. QFNs give compact size and good thermal performance. BGAs give the highest connection density but place the most demands on PCB design and inspection.
BGA and QFN packages in your quote request
In your quote request, list the BGA and QFN parts in the BOM with their exact MPNs, and state if X-ray inspection is required for all boards or as a sample. Include any via-in-pad or filled-via requirements in your fabrication notes, and mention if you have special stencil or thermal pad requirements. Our free DFM check flags footprint, solder mask and via issues around these packages before the files go to a manufacturer.
Need boards assembled? Send your Gerber files and BOM for a free turnkey quote from the right assembly partner.
PCB assembly →FAQ about BGA and QFN packages
What is QFN packaging?
QFN, or quad flat no-leads, is a surface-mount IC package with flat terminals on the underside along all four edges instead of protruding leads. Most QFNs also have a large exposed pad in the centre that is soldered to the PCB for heat dissipation and grounding. The package is small, thin and has good thermal and electrical performance.
What are the key differences between BGA and QFN packages?
A BGA connects through an array of solder balls across its underside, giving very high pin counts in a small area. A QFN has a single row of flat pads at its edges and usually a central thermal pad, so it suits lower pin counts. BGAs need X-ray inspection and often more PCB layers; QFN edge joints can be partly inspected visually.
What is the difference between QFN and DFN?
QFN and DFN are both leadless surface-mount packages with flat terminals on the underside. QFN, quad flat no-leads, has terminals on all four sides. DFN, dual flat no-leads, has terminals on two opposite sides only. DFNs are typically used for parts with fewer connections, such as small regulators, MOSFETs and sensors.
Why do BGAs need X-ray inspection?
BGAs need X-ray inspection because their solder joints are hidden under the package body, so they cannot be checked visually or by AOI. X-ray shows the shape and alignment of each ball and reveals defects such as bridging, missing balls, voids and some open joints. Head-in-pillow defects can be harder to detect and may require angled X-ray views.
Related terms
- X-ray inspection
X-ray inspection is a non-destructive testing method that penetrates the PCB to reveal hidden solder joints under BGAs, QFNs, and other bottom-terminated packages. It detects voids, head-in-pillow defects, bridging, and missing joints that AOI cannot see. Available in 2D (top-down) and 3D CT (full volumetric) variants.
- Reflow soldering
Reflow soldering is the process used to solder surface-mount components to a PCB. Solder paste is printed onto the pads, components are placed on the paste, and the board passes through an oven that follows a controlled temperature profile. The paste melts, wets the pads and leads, and forms solder joints as it cools.
- Stencil
A stencil is a thin laser-cut steel sheet with apertures matching the SMT pads on the PCB, used to apply solder paste precisely before component placement. Typical thickness is 100-150 µm. Stencil aperture design affects solder paste volume and is critical for fine-pitch BGAs and QFNs to prevent insufficient solder or bridging.
- HDI
HDI (High Density Interconnect) describes PCBs with significantly higher routing density than conventional boards, achieved through microvias, thinner traces, and sequential lamination. HDI is essential for high pin-count BGAs, compact electronics, and applications in smartphones, medical devices, automotive ECUs, and aerospace systems.
- Microvia
A microvia is a small laser-drilled blind via, typically 150 µm or less in diameter (per IPC-T-50M definition), used to connect adjacent layers in HDI boards. Microvias enable routing for high pin-count BGAs and densely packed components that conventional mechanical vias cannot support.
- SMT
SMT (Surface Mount Technology) is the dominant PCB assembly method where components are placed directly onto the surface of the board and soldered using reflow ovens. It enables smaller, denser, double-sided boards and supports nearly all modern component packages including BGAs, QFNs, and 0402 passives.