Identify failure risk to improve reliability

Unlike other NDT technologies, the Insidix TDM (Topography and Deformation Measurement) system is a predictive tool capable of identifying weaknesses or failure risks resulting from thermal stress before physical damage actually occurs.

Electronic systems, with increasingly complex components and assemblies, contain a great variety of different materials, each of which responds differently to the increasingly high heat levels introduced during assembly or in the normal operation of the system. These differential responses to heat variations create internal stress that may result in a variety of failures, such as delaminations inside the IC’s, incomplete soldering of BGA solder ball arrays (contacts poorly soldered or stay open), premature aging of solder joints with increased risk of rupture, etc.

Even before physical failure occurs, the thermal stress experienced by the components or assemblies gives rise to volume deformation (“warpage”), which can be considered a precursor of failure, in other words a failure risk indicator. The TDM system was designed to allow the development engineer to use the measurement of these deformations to identify failure risks and improve the reliability of his product. TDM can accurately replicate the thermal profiles and cycles that the components or assemblies will actually experience during the production process and in normal use. Throughout the thermal cycle, TDM measures the 3D deformation related to the imposed thermal stress, thus revealing faults that would likely occur during normal production and use.

The TDM system represents the state of the art solution for 3D deformation analysis under thermal stress conditions. The general principle is shown below. The system combines a powerful heating and cooling system (temperature range -60°C … +300°C) with a real time acquisition of the 3D topography of virtually any kind of sample (respecting the limitations of maximum size of up to 400 × 400 × 50 mm). In particular, strongly structured samples like TSOP components with their several tens of tiny connectors or even PGA bottom sides with their hundreds of 2-3 mm long pins are resolved with the same precision as simple flat BGA top sides.

TDM’s topography acquisition is based on the Projection Moiré principle: Structured light is projected onto the sample by means of a programmable light projector, at a projection angle of typically 45° (see below). The image is captured by a CCD camera. The striped pattern seen by the camera is characteristic of the sample’s surface structure. On perfectly flat and horizontal surfaces, the light pattern visible on the sample surface would be a set of equidistant, parallel stripes. Any deviation of the sample away from perfect flatness will lead to variation of the observed strip pattern. In the case of a simple step, as depicted in the figure, there will be two distinct patterns of equidistant, parallel stripes, with an offset between the two stripe patterns at the place of the step. The amount of the offset is directly related to the height of the step.

In practical applications, a succession of several stripe systems is projected onto the surface under test, with the wavelength of the light structure varying from wide to short. In this way, TDM is able to simultaneously measure the absolute height of vertical steps of up to 25 mm, and at the same time allow z-height resolutions in the order of some µm.

All TDM system components used for the imaging process are far away from the sample under test, and in no direct contact with the latter. The only condition for 3D acquisitions with the Projection Moiré principle is that the two lines of sight linking respectively the projector and the CCD camera to the sample stay unobstructed. All the other space can be used for other requirements. The TDM system is therefore able to place heating and cooling elements on both sides of the sample, bottom and top. Additionally, top and bottom side heating elements feature independent feedback loops for temperature measurement (by thermocouples) and regulation, resulting in perfect homogeneity of top and bottom side sample temperatures. No other available commercial topography measurement system provides this capability. The target temperature profile can be programmed to fit any type of application. User defined temperature profiles with heating gradients up to +3°C/s and cooling gradients down to -6°C/s may be imposed, within a temperature range of -60°C up to +300°C. The specified temperature homogeneity is +/-5°C on the entire sample (top and bottom side), and the typically obtained temperature homogeneity is significantly better.

Simultaneously, at any moment during the temperature progression, snapshots of the 3D sample surface topography can be taken, as shown below for the case of a fully equipped board. High resolution imaging is obtained by the use of 4 MPixel or higher CCD cameras. The high depth of view of the optical set-up allows acquisition of all relevant levels of the component or assembly simultaneously. For each pixel, the (x,y,z) coordinates are absolutely known. Zoom optics can then limit the field of view exactly to the zone of interest on the sample to reveal detailed surface information. The depth of view (efficiently available z-scale) is virtually unlimited (25 mm and higher), with full z-resolution of down to some few µm.

The TDM system permits the identification of failure risks in an early stage of the development process. The benefits to the customer relate to reduced development time, reduced time to market, reduced failures and increased reliability of both the assembly process and the product during its operating lifetime. Some of the specific analysis applications for TDM are listed below and discussed in detail in the application documents and technical papers listed in the center column. The application discussions included in the technical papers are as follows:

EDFAS Journal 2011

TSOP Contact Level Topography Analysis during Reflow
High Pin Count BGA Ball Coplanarity
Component Solder Conditions Optimization
Component-to-PCB Stress Transfer