AIRBUS Defence and Space – Print process characterization for aerospace Printed Circuit Boards, with PI Series

AIRBUS Defence and Space – Print process characterization for aerospace Printed Circuit Boards, with PI Series

Fri / 04 / 2016,

Author : Benjamin Münch Production methods engineer, Airbus Defence and Space, Elancourt (France).             Airbus Defence and Space – Presentation : Airbus Defence and Space is a division of Airbus Group formed by combining the business activities of Cassidian, Astrium and Airbus Military. The new division is Europe’s number one defense and space enterprise, the second largest space business worldwide and among the top ten global defense enterprises. It employs some 40,000 employees generating revenues of approximately €14 billion per year. The Elancourt plant is the competence center for electronics production, which is the high-tech sector of AIRBUS Defence and Space. Some of its activities are design, development and production of electronics systems or advanced components (hybrid, multi-die). Products manufactured at Elancourt: The Elancourt (France) site is manufacturing Printed Circuit Boards for satellites and military equipment. The yearly production capacity is 300 to 400 highly complex boards, combining advanced innovations with conventional methods. Each board represents a value of several hundred thousands of Euros, and is capable of sustaining extreme constraints associated with space environment (mechanical, thermal…).   Airbus Defence and Space and Vi TECHNOLOGY partnership : Early 2014, Airbus Defence and Space was looking for a partner able to deliver advanced solutions for 3D Solder Paste Inspection (3D SPI), with high level of technical expertise, to characterize the print process for PCBs used in aerospace applications. In June 2014, following the presentation of Vi TECHNOLOGY’s PI Series innovative product family for 3D Solder Paste Inspection, Airbus Defence and Space and Vi TECHNOLOGY started collaborating to deliver an extremely accurate paste measurement system. PI Series offers a patented Z-referencing method, allowing unrivaled accuracy for height and volume measurement of paste deposits. Vi TECHNOLOGY conducted preliminary analysis in their R&D center in France to highlight PI Primo capabilities on our highly complex PCBs. In September 2014, following encouraging preliminary results, we decided to evaluate the PI Primo machine in our Elancourt premises.   Characteristics of PCB for aerospace applications : Printed Circuit Boards for aerospace applications have numerous differences with PCBs used in conventional applications (industrial, medical…). Our boards are made with polyimide, without solder resist, and with a tin-lead finishing which may vary from one board to another. Absence of solder resist renders the print process complex and as a result, leads to specific defects.   Why we chose PI Primo ? Our premium 3D Solder Paste Inspection systems’ benchmark revealed unique characteristics of PI Primo which were important to us:

  • With an ultra-large Field Of View, the full 3D image covers not only one pad but several pads,
  • This machine operates solely with a touch screen, icon based interface allowing anyone to be up and running after just an hour’s training,
  • The patented Z-referencing technology, completely independent from the operator’s experience, allows high confidence level on delivered measurement,
  • The unneeded paste color teaching which is required on most of other machines,
  • The possibility to group pads having the same characteristics, i.e. same AAR (Aperture Area Ratio), significantly simplifies data analysis.

In addition, the bare board teaching technology, based on powerful algorithms, determines the Z-reference (level 0) with accuracy, which is the mandatory step to measure correctly any paste height and then volume, even on boards having severe warpage.   Print process characterization with PI Primo : Increasing component density and decreasing number of traces (on top layer) on our Printed Circuit Boards, require stringent control of our print process, a key to ensure ultimate quality levels for aerospace applications. The large 3D image combined with accurate measurements allowed us to identify and visualize specific defects related to our process, and most importantly to find their root cause. We decided to implement a specific test plan to optimize completely our print process, i.e. to optimize the filling ratio of all pads.   Test plan : We modified the following print process parameters to measure accurately impact on all deposits:

  • Squeegee speed,
  • Angle between squeegee and stencil,
  • Squeegee size and associated pressure.

PI Primo allowed us to plot the measured value for solder paste location, area, volume, and shape… versus targeted values for each pad. With appropriate analysis, we succeeded to define the best set of print parameters to optimize filling of large pads’ edge. We also adjusted the printer cleaning cycle, to sustain high quality level of prints.   Print process parameters optimization :                                3D image before correction   “dog bone / dog ear” defect                                 3D image after correction  Optimized filling on edges Continuous improvement : We also developed an appropriate procedure to ensure a high quality and a repeatable print process year round. Once a month we use a reference-PCB, together with reference-stencil. We print this PCB with this stencil and we measure the solder paste of each pad, including the X-Y offsets. Then, quarterly, we present those results to our internal customers to certify our process stability. Print process improvements :                                

Filling ratio (AAR < 2.1)

September 2015 : New print process parameters’ implementation.

The filling ratio is now almost 100%, with much better standard deviation.

What is next ? The next step will be to modernize and automate our production area with the acquisition of new conveyors to connect our PI Primo directly to other machines. Therefore, we aim to define the methodology to maximize benefits from an in-line PI Primo:

  • Bare board teaching from representative PCB or from current PCB,
  • Bare board teaching of second PCB side before or after the first reflow.

The final stage will be to define our inspection criteria for solder paste area, volume, offsets and shape to allow each board to move forward in the production flow.