LGA Assembly Without Solder Balls

What an LGA Package Is

A land grid array package has a grid of flat pads on its underside instead of solder balls. The connection is formed entirely by the paste printed on the board, which melts, wets the package pads, and forms the joint. There is no ball to provide standoff, and no ball to collapse and absorb a difference in height.

That difference from a ball grid array is the source of everything that makes LGA assembly demanding. A BGA arrives with a defined standoff created by the balls, and the joint forms as the balls collapse. An LGA has no such feature, so the joint height and the contact between the package pad and the paste depend entirely on the paste volume and on the flatness of both surfaces.

LGAs are used where the package must be very thin, where a socket will hold it, or where the ball height is not acceptable for the application. Some socketed processors are land grid arrays, and some sensors and modules use the same construction.

Why Land Grid Arrays Are Used

The first reason is height. Removing the balls reduces the stack height of the package, which matters in thin products. The second is that a flat land pattern is easier to socket, because the socket contacts can press directly on the pads without the alignment problems that balls present.

The third is electrical. A shorter connection path reduces inductance, and the flat land pattern can support a finer pitch than a ball array, which allows more connections in the same area. For high pin count devices, that density is valuable.

The trade-off is assembly difficulty. The absence of balls removes the tolerance that a collapsing ball provides, so the process has to be more precise in paste volume, placement, and board flatness. That is why LGA assembly is often paired with a socket rather than being soldered directly.

Paste and Stencil Requirements

The paste volume determines the joint height and the contact area, so the stencil has to deliver a consistent, well-controlled deposit. There is no ball to compensate for a short deposit, so a low volume produces an incomplete joint and a high volume produces a ball that can bridge to a neighbour.

The stencil thickness and the aperture size are chosen together to give a printable area ratio and the correct volume. Because the pitch is often finer than a comparable BGA, the aperture is small and the stencil must be thin, which reduces the volume available. The design has to balance the two.

The quality of the pad surface on the package also matters. A land that is oxidized or contaminated will not wet, and there is no ball to hide the problem. The paste flux has to be able to clean the pad during reflow, which favours a more active flux than a low-activity alternative.

Placement and Coplanarity

Coplanarity is the dominant mechanical issue. If the package is not flat, or the board is not flat, the gap between the package pads and the paste varies across the array, and some joints form while others do not. Unlike a ball array, an LGA cannot compensate for that variation by collapsing.

Placement force and accuracy are therefore critical. The package must be placed with enough force to ensure contact between the paste and the pads without squeezing the paste out, and the position must be accurate because there is no self-centring from the surface tension of a large ball. Vision alignment should be used, and the placement force should be controlled and monitored.

Board flatness is also part of the design. A thin board, an asymmetric stackup, or a large copper area on one side can cause warpage that shows up as a coplanarity problem on the assembly. Where the package is large, the board should be supported during reflow and the stackup should be balanced.

Reflow and Self-Centering

Self-centring is weaker for an LGA than for a ball array. In a BGA, the molten balls provide a large restoring force that pulls the package back to the pad centres. In an LGA, the restoring force comes only from the small fillet at each land, so the package has less ability to correct an offset during reflow.

The profile has to bring the whole array to liquidus at the same time. A large LGA package on a board with heavy copper can develop a temperature gradient across the array, and the joints that melt first will pull the package before the others melt. A slower soak and a gradual ramp reduce the gradient.

Where the package is socketed rather than soldered, the reflow requirement disappears, but the mechanical requirement remains: the socket must apply a uniform force across the land pattern, and the package and the socket must be coplanar. A socket that loads unevenly produces intermittent contacts that appear as a thermal or electrical problem rather than a mechanical one.

Inspection and Rework

The joints are under the package and are smaller than a BGA joint, so X-ray is the primary inspection method. The fine pitch makes the images harder to interpret, and the void level and the wetting have to be assessed against a known-good reference rather than by eye alone.

Rework is more difficult than for a BGA because there is no ball to re-form the joint. The site has to be cleaned and fresh paste applied before the new package is placed, which means the rework must reproduce the original print step on a populated board. That is a demanding operation and should be documented and limited.

Because of the difficulty, the emphasis is on getting the first assembly right. Stencil design, paste volume, placement force, board flatness, and the reflow profile are all variables that have to be controlled, and the inspection is there to confirm the result rather than to find the problem.

FAQ

What is the difference between an LGA and a BGA? A BGA has solder balls that provide the standoff and collapse during reflow. An LGA has flat land pads and relies entirely on the printed paste to form the joint.

Why is LGA assembly harder? Because there is no ball to absorb differences in height, paste volume, or flatness. The process has to be more precise in every dimension.

Do LGAs self-centre during reflow? Less than a BGA. The restoring force comes only from the small fillets at the lands, so the placement has to be accurate and the profile uniform.

How are LGA joints inspected? By X-ray, with the results compared against a known-good reference because the pitches are fine and the interpretation is difficult.

Is LGA rework practical? It is demanding because paste must be re-applied on a populated board before the new package is placed. It should be documented and limited rather than treated as routine.

Conclusion

LGA assembly removes the solder ball that gives a BGA its tolerance, and replaces it with a process that depends on paste volume, coplanarity, placement, and a uniform profile. The result is a thin, dense connection that is well suited to sockets and thin products, and it demands more control than a comparable ball array. For related topics, read our notes on SMT assembly, PCB assembly, PCBA testing, and PCB capabilities for how fine-pitch packages are assembled in 2026.