mobile | classic
Dataweek Electronics & Communications Technology Magazine





Follow us on:
Follow us on Facebook Share via Twitter Share via LinkedIn


Search...

Electronics Buyers' Guide

Electronics Manufacturing & Production Handbook 2017


 

Printing using micro stencils for LGA/QFN rework
EMP 2018 Electronics Manufacturing & Production Handbook, Manufacturing / Production Technology, Hardware & Services

If you are repairing land grid array (LGA) or area array devices, should you print the circuit board or the device terminations?

Either method can work, with your own skills determining which is easier and more repeatable.

Recent hands-on rework workshops proved very successful for the author and delegates reworking these fairly new packages. Special thanks go to TECAN in the UK for making the handheld manual rework foils specifically designed for QFN (quad flat no-lead) and LGA packages. Let us now step through the process in this step-by step-guide.

Figure 1. Hand print stencil for land grid array package with a 0,004” foil.
Figure 1. Hand print stencil for land grid array package with a 0,004” foil.

Firstly, make sure that the solder paste being used in rework is the same as in production. Often a dispense grade with larger ball size or lower metal content is used in repair areas but may not be suitable for stencil printing these fine pitch parts.

Select a micro stencil for the component footprint for a land grid array; this would normally be 0,004” (100 μm) foil (Figure 1). The stencil apertures for the outer pads are produced as one to one apertures. The centre aperture can be single or multiple apertures to cover between 50% and 60% of the surface area. It is recommended to have the paste printed to the centre of the device, not to the edge of the centre pad.

The stencil, being very thin, has a backing foil of between 0,010” and 0,012” thick and allows the stencil to be used for manual hand printing.

Figure 2. Laminated support foil welded to stencil foil providing a location for the package alignment.
Figure 2. Laminated support foil welded to stencil foil providing a location for the package alignment.

The thicker support foil (Figure 2), prevents the image foil being flexed during printing, which can lead to inconsistent deposits. The support foil also allows the component to be positioned accurately to the terminations (Figure 3).

Figure 3. LGA is located in the support foil cavity for printing.
Figure 3. LGA is located in the support foil cavity for printing.

Place the LGA/QFN component into the stencil guide and check the right stencil is being used and the apertures are perfectly aligned with the terminations. One finger can be used to hold the component in position while the stencil is turned over for printing (Figure 4). Alternatively a small piece of Kapton tape can be used to hold the part in position.

The component can now be printed with solder paste using a small metal rework squeegee blade. It is important to use the blade in the same way as a printer; make sure the paste is rolling and the surface of the stencil is clean after the print stroke. Inspect to confirm that the paste is completely filling the apertures.

Figure 4. Stencil is turned over while still holding the LGA in place and manually printing with solder paste.
Figure 4. Stencil is turned over while still holding the LGA in place and manually printing with solder paste.

Before printing solder paste onto components, try printing paste images onto a flat surface like copper clad laminate, glass or thick white card. This will allow an opportunity to perfect the repair printing process. When the correct technique has been mastered, check the cleanliness of the stencil apertures and base to prevent contaminating the component surface with paste.

Figure 5. The LGA is lifted from the cavity and placed on the printed board for reflow. Alternatively the stencil is located on a rework system so the machine can lift the printed component directly and place the part on the surface of the board.
Figure 5. The LGA is lifted from the cavity and placed on the printed board for reflow. Alternatively the stencil is located on a rework system so the machine can lift the printed component directly and place the part on the surface of the board.

Turn the stencil over so the part can be lifted prior to placement (Figure 5). If the component is lifted manually it can be inspected visually prior to placement on the board. If the stencil is going to be located on a rework system the component can be placed automatically, and inspection of the paste deposits can be conducted on the rework system when the component is aligned with the pads prior to placement.

Make sure you check the stencil after use and clean or check for paste remaining in apertures if you intend to print a second device. Paste release from the stencil is just as important as printing in normal manufacture to achieve the best yields.

Another option is to jet print the solder paste directly to the board or on the surface of the component, just like manual printing. There are two or three jetting systems on the market today, one of which is a benchtop system which is perfect to use for rework or bumping packages.

Figure 6. Close up of dummy LGA package used in training and printed with paste.
Figure 6. Close up of dummy LGA package used in training and printed with paste.

Bumping QFN/LGA packages can improve reliability and decrease voiding during reflow.

For more information visit www.bobwillis.co.uk


  Share on Facebook Share via Twitter Share via LinkedIn    

Further reading:

  • From zero to 100 million placements a month in 25 years
    18 July 2018, Microtronix Manufacturing, Manufacturing / Production Technology, Hardware & Services
    Microtronix CEO, Mike Goodyer, tells the story of the company’s remarkable journey to becoming an electronics manufacturing force to be reckoned with.
  • Designing high-speed PCBs using four layers
    18 July 2018, EDA Technologies, Manufacturing / Production Technology, Hardware & Services
    There is an ever-growing demand for high-performance electronics products to use printed circuit boards with an absolute minimum layer count.
  • Flying probe tester
    18 July 2018, MyKay Tronics, Manufacturing / Production Technology, Hardware & Services, Test & Measurement
    The Flying Probe S2 testers from SPEA are designed for the highly demanding test requirements of today’s electronics. Their entire force/measurement unit has been placed directly on the axis, so that ...
  • Contactless SMD component counter
    18 July 2018, Testerion, Manufacturing / Production Technology, Hardware & Services
    The XRHCount from VisiConsult is a contactless counting system for surface mounted electronic components. To prevent production line stops the system delivers the exact amount of components directly into ...
  • Factory in a box
    18 July 2018, Techmet , Manufacturing / Production Technology, Hardware & Services
    Mycronic has joined a Nokia-led group of 12 electronics industry players to offer a plug-and-play ‘Factory in a Box’ mobile solution for next-generation electronics assembly. The fully automated in-line ...
  • Printer for professional 3D printing
    18 July 2018, RS Components (SA), Manufacturing / Production Technology, Hardware & Services
    The Ultimaker S5 3D printer targets the professional end of the market across a number of applications and meets engineering requirements from the creation of prototypes to full end-use, industrial-grade ...
  • Cleaning agent concentration tester
    18 July 2018, Electronic Industry Supplies, Manufacturing / Production Technology, Hardware & Services
    The Zestron EYE product family celebrated its latest automated cleaning agent monitoring solution for PCB and stencil cleaning processes at SMT Hybrid & Packaging 2018 in Nuremberg. In addition to the ...
  • Automated fluid dispensing platform
    18 July 2018, Techmet , Manufacturing / Production Technology, Hardware & Services
    Nordson ASYMTEK’s Helios SD-960 series is a new automated dispensing system for medium and bulk volume deposits of single- (1K) and two-component (2K) materials in electronics manufacturing and printed ...
  • Soldering station for heavy-duty production
    18 July 2018, MyKay Tronics, Manufacturing / Production Technology, Hardware & Services
    PACE Worldwide introduced the ADS200, a new high-power, low-cost production soldering station, at the IPC APEX Expo 2018. The ADS200 features the new TD-200 Cool-Touch Handpiece, with its sleek and ...
  • Fused filament 3D printer
    13 June 2018, RS Components (SA), Manufacturing / Production Technology, Hardware & Services
    The new easy-to use RS Pro iTX 3D printer from RS Components targets a wide range of users in manufacturing and many other commercial and business applications, as well as being suitable for educational ...
  • Newest Yamaha SMT machines shown off
    13 June 2018, Truth Electronic Manufacturing, Manufacturing / Production Technology, Hardware & Services
    Yamaha Motor Europe debuted new printing, 3D print inspection and mounting machines at this year’s SMT Hybrid Packaging show in Nuremberg, all featuring innovations to boost productivity and efficiency. Headlining ...
  • Enabling power electronics advancement through thermal management
    13 June 2018, Vepac Electronics, Manufacturing / Production Technology, Hardware & Services, Power Electronics / Power Management
    From power management and distribution of renewable energy sources, through to electric vehicle development and even wireless phone charging, power electronics and associated research is a dominant trend. ...

 
 
         
Contact:
Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Other
Terms & conditions of use, including privacy policy
PAIA Manual





 

         
    Classic | Mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.