פתרונות בקורת איכות צב"ד ייעודי

A typical GUI of a parametric tester – provides scaled results of relevant parameters

Process control by parametric  test jigs
 תכנון צב"ד אלקטרואופטי ביקורת איכות
Machine vision test jig for QC of an injected lens. Makes use of several resolution targets
Process analysis yield improvement ISRAEL
Process analysis indicates where test steps are needed
Custom Parametric testing

 

CSTM’s process support
CSTM specializes in definition design and implementation of parametric testers. CSTM cooperates closely with the product manager and the production engineers (QA  engineer, process engineer) in order to improve yield.

 

About parametric test equipment
A parametric tester has the following characteristics:
• simultaneous sampling of multiple parameters
• user selected grouping scale (to associate tested items with quality groups)
• generates a results log
• Built-In-Test capability by use of Golden samples

 

Parametric test equipment applications
Unlike threshold based Go-NoGo testers, parametric testers provide quantitative data regarding the quality level of the product under test. Parametric test equipment is a first-class tool for the process engineer and the QA engineer which are both responsible for the process yield, allowing them to perform the following activities:
• research points for improving  the process (by evaluation of trial & error rounds)
• locating an optimal robust working point and monitoring its drift
• failure analysis – post failure detection of  gradual deterioration using a selected parameter set
• parameter monitoring – discovering process instabilities due to competing parallel processes, and improving process convergence.
• monitor parameter distribution for CPK analysis
• product sorting – grouping (binning) the resulting output items
• generate a quality based feedback (rather than an external parameter based feedback)

 

Example of a problem solved by a parametric tester
A custom tester for monitoring the quality of an injection molded miniature camera, was used for final testing of the assembled camera.  The quality of the final camera was sensitive to changes in two angles, Tilt and Pitch, which were monitored to an accuracy of 0.25mRad. Tilt  is defined as the angle of rotation of a target image about the optical axis.  Pitch  is the linear vertical shift  of a target image relative to its desired position (a kind of Boresight angle).
Fig.1 shows raw results of gathering the Tilt\Pitch data for a batch of cameras.

Data acquisition QC testers Israel

Fig.1: Boresight measurement in cameras – monitor the Optical to Mechanical axis alignment

The results in blue are the raw results, and green and red results show histograms of the Tilt angle and Pitch angle respectively.
These Histograms are close to a bell curve distribution as expected. Furthermore, it is seen that the Tilt curve is closer to a bell curve than the Pich curve, and much more centered. Therefore, it was decided to carefully monitor the more stable Tilt, to see if any changes occur during production.
Searching for a stable working point, revealed a state in which the production hits instability. The tester discovered (see Fig.2) a split of two competing sub-processes (bistable process) which expressed itself as two overlapping bell-curves. This discovery suggested that the injection process was oscillating between two modes. Finding and rectifying the problem increased the yield.

Process Failure analysis QC testing

Fig.2: Parametric test jigs supply quantitative results for monitoring process stability