Common sense of circuit board: how to strengthen PCB circuit board BGA to prevent cracking

Common sense of circuit board: how to strengthen PCB circuit board BGA to prevent cracking

BGA cracking is one of the most common reliability failures in PCB assembly. Cracks in BGA solder balls usually lead to intermittent open circuits or complete product failure. ONESEINE TECHNOLOGY CO.LTD shares practical engineering methods to reinforce PCB BGA structure and avoid cracking problems from multiple dimensions, including improving PCB deformation resistance, reducing external stress and optimizing BGA solder joint reliability.

1. Enhance PCB's ability to resist deformation

PCBA deformation is mainly triggered by thermal expansion and contraction during high-temperature reflow soldering. Uneven component layout and unbalanced copper foil distribution on the board will further aggravate board warpage. The following solutions can effectively improve the anti-deformation performance of the PCB.

Increase PCB board thickness. Where design space permits, a PCB thickness of 1.6mm or above is recommended. If thin boards of 0.8mm, 1.0mm or 1.2mm have to be adopted, furnace fixtures are strongly suggested to support the board during reflow to minimize warpage.

Adopt high Tg PCB substrate materials. Materials with high Tg value deliver higher rigidity to resist thermal deformation, though the material cost will rise accordingly. Engineers need to balance performance and budget in the project selection.

Apply epoxy potting compound. Epoxy glue can be dispensed around the BGA component or on the corresponding back side of the PCB to boost stress resistance of the BGA area.

Add steel reinforcing bars around BGA. If there is sufficient layout space, a supporting steel frame can be arranged surrounding the BGA to strengthen its stress bearing capacity, similar to adding reinforcement bars in building construction.

2. Reduce PCB deformation caused by external forces

After PCB assembly, the board is enclosed inside the product housing which provides basic protection. However, portable and slim electronic products are vulnerable to bending force or drop impact, which will bend the PCB and crack BGA solder joints. The below mechanical design measures help mitigate external stress.

Reinforce the product housing. A sturdy shell can avoid housing deformation transferring bending stress to the internal PCBA.

Add screws or positioning fixtures around BGA. Fixing the PCB near the BGA area restricts local deformation and protects BGA solder balls from excessive stress.

Adopt mechanical buffer design for PCBA. Cushioning materials can be deployed between the housing and circuit board. Even if the shell deforms under impact, the buffer layer isolates the PCB from external force. Service life and compression performance of the cushioning material should be fully evaluated in advance.

3. Enhance the reliability of BGA solder joints

Apart from board and mechanical optimization, optimizing BGA pad layout and soldering process can greatly improve solder joint robustness.

Implement BGA underfill. Inject underfill adhesive beneath the BGA package to encapsulate solder balls, disperse thermal and mechanical stress and prevent solder crack.

Use SMD (Solder Mask Defined) pad design. Cover non-soldering areas of pads with green solder mask.

Properly increase solder volume. The solder amount needs precise control to eliminate the risk of short circuit between adjacent balls.

Enlarge PCB BGA pad size. Larger pads improve solder joint strength, but this will reduce the routing space between BGA balls and bring challenges to PCB trace layout.

Apply Vias-in-pad (VIP) design. Vias on BGA pads must be fully filled by electroplating. Unfilled vias will generate air bubbles during reflow process, which easily cause solder ball fracture. This principle is just like solid piling foundation for buildings.

Stress test simulation is highly recommended for finished products. Engineers can use stress gauges to locate stress concentration zones on PCBA. If physical testing is unavailable, computer simulation software can predict potential high-stress regions at the design stage.

To sum up, BGA cracking prevention is a systematic work covering PCB material selection, stack-up design, mechanical structure and assembly process. ONESEINE TECHNOLOGY CO.LTD recommends PCB designers and hardware engineers to evaluate stress risk at the early design phase to reduce BGA failure risks in mass production.

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