Zero defect manufacturing is not an aspiration in aerospace electronics, it is a contractual and regulatory requirement. A solder joint failure in an avionics assembly does not produce a warranty claim. It produces an airworthiness investigation. The combination of safety criticality, long service life requirements and the increasing prevalence of high-density packaging in modern avionics is driving aerospace electronics manufacturers toward inspection technologies that can verify every joint on every board, not just a statistical sample. For BGA and other bottom-terminated packages, that means 3D automated X-ray inspection.
The Inspection Challenge in Modern Avionics
Avionics assemblies have historically favoured through-hole and leaded surface mount components, which offer robust solder joints that are straightforward to inspect visually. That is changing. Miniaturisation pressures, weight reduction targets, and the demand for higher processing capability in smaller form factors are driving avionics designers toward the same high-density packages used in consumer and telecommunications electronics. BGAs, QFNs, land grid arrays, and other bottom-terminated devices are now common in avionics assemblies, and every one of them presents a solder joint that is completely hidden from optical inspection once the component is placed.
This is not a minor gap in inspection coverage. It is a fundamental limitation. AOI systems , regardless of their sophistication — cannot see underneath a component body. Flying probe testing can identify electrical failures but cannot detect marginal joints that will pass initial electrical test and fail in service under vibration or thermal cycling. The only non-destructive method that provides direct visual and dimensional data on hidden solder joints is X-ray.
Why 3D Rather Than 2D X-Ray
Conventional 2D X-ray inspection has been used in electronics manufacturing for decades, and it provides useful information about hidden joints. Its limitation in the aerospace context is the ambiguity that comes from projecting a three-dimensional assembly onto a two-dimensional image. Solder from joints on opposite sides of the board overlaps in the image. Component bodies cast shadows. The precise geometry of individual ball joints in a BGA array, the information needed to make a reliable acceptance decision is difficult to extract from a flat projection, particularly on double-sided assemblies.
3D AXI addresses this through computed laminography, reconstructing a three-dimensional model of the assembly from multiple X-ray projections taken at different angles. This allows the system to examine individual slice planes through the assembly, isolating specific solder joint layers and measuring void percentage, ball diameter, coplanarity, and joint geometry with precision. The result is a quantitative, unambiguous measurement of joint quality for every ball in every BGA array on the board.
Voiding Standards and Traceability
Voiding, gas pockets within the solder ball is one of the primary quality concerns in BGA assembly for aerospace applications. IPC-7095 provides guidance on acceptable void levels for different joint types and applications, and aerospace customers frequently impose their own, more stringent limits. 3D AXI provides the precise, per-joint void percentage measurements needed to demonstrate compliance with these requirements, with results stored in a traceable record linked to the individual board serial number.
This traceability is central to the aerospace quality requirement. When a platform is in service for twenty or thirty years, the ability to retrieve inspection records for a specific assembly and demonstrate that it met the required acceptance criteria at the time of manufacture has significant value in managing airworthiness risk.
100 Percent Inspection as the Standard
In many industries, AXI is used for process monitoring on a sampling basis. In aerospace electronics manufacturing, the direction of travel is firmly toward 100 percent inline inspection of every board. Automated inline 3D AXI systems are now fast enough to keep pace with modern SMT line outputs without becoming a throughput bottleneck, removing the statistical risk inherent in sampled inspection and providing a complete board-by-board quality record for every assembly shipped.
Omron’s 3D automated X-ray inspection systems are available in the UK and Europe through Etek Europe. For specifications and application support for aerospace and defence programmes, visit www.etek-europe.com or contact sales@etek-europe.com.
