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:

  • 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 ...
  • Open SMT assembly standard enjoying strong uptake
    18 April 2018, Manufacturing / Production Technology, Hardware & Services, News
    The standard can be adopted by any equipment manufacturer without any licence fee, and already counts nearly 30 vendors among its members.
  • Local manufacturers look forward to a brighter future
    21 March 2018, Omnigo, SMTech, Grand Tellumat Manufacturing, This Week's Editor's Pick, News, Manufacturing / Production Technology, Hardware & Services
    Dataweek interviewed three South African electronics contract manufacturers to find out what they’ve been up to lately, and what their outlook is.
  • Lessons learned from an ECM and the customer that sued them
    21 March 2018, MyKay Tronics, This Week's Editor's Pick, Manufacturing / Production Technology, Hardware & Services
    The plaintiff created a new technology that consisted of a sensor and a receiver, but lacked the ability to produce it. Enter the contract manufacturer, soon to be the defendant.
  • Manufacturing islands employed in Siemens IPC production
    21 March 2018, Quamba Technologies, Manufacturing / Production Technology, Hardware & Services
    Siemens industrial PCs (IPC) have been leading trends for over 30 years. As early as 1983, Siemens started combining standard PC technology with characteristics that fulfilled demanding industrial requirements, ...
  • Panasonic placement machine wins global award
    21 March 2018, Techmet , Manufacturing / Production Technology, Hardware & Services
    The machine is the latest stage in the evolution of the NPM series and is geared for manufacturers who value setup and changeover time over speed. “The NPM-W2S was designed to solve manufacturer’s need ...
  • I had to eat my words
    21 March 2018, EDA Technologies, Manufacturing / Production Technology, Hardware & Services
    In the middle of 2017, I wrote a piece for Dataweek entitled ‘Celebrating 20 years of disruptive electronics’ wherein I concluded with the words: “Disruptive electronics can only really be made possible ...
  • Modular component mounter
    21 March 2018, Techmet , Manufacturing / Production Technology, Hardware & Services
    Panasonic’s modular NPM-D3 component mounter is equipped with all the cutting edge technology demanded of modern electronics manufacturing equipment. The system’s lightweight, 16-nozzle head combines ...
  • Cogiscan and Universal Instruments partner up
    21 March 2018, Zetech, Manufacturing / Production Technology, Hardware & Services
    Cogiscan, a specialist track, trace and control (TTC) solutions provider for the electronics manufacturing industry, has signed an OEM reselling agreement with Universal Instruments to expand its portfolio ...
  • Reflow oven for high-volume production
    21 March 2018, MyKay Tronics, Manufacturing / Production Technology, Hardware & Services
    BTU International exhibited its new Pyramax Vacuum reflow oven at this year’s IPC APEX Expo. Designed around the requirements of large EMS/high-volume automotive customers, the unit is configured with ...
  • 3D AOI system measures component height
    21 March 2018, Techmet , Manufacturing / Production Technology, Hardware & Services
    Saki’s BF-3Di is an automatic optical inspection (AOI) machine that not only performs inspection, but also provides measurements of each component for heights from 0 mm to 20 mm, with 1 micron height ...
  • New capabilities at Omnigo
    21 March 2018, Omnigo, Manufacturing / Production Technology, Hardware & Services
    Omnigo has grown tremendously of late, and to address this rapid growth the company had to make some astute equipment investment decisions. The specific niche market in the electronics contract manufacturer ...

 
 
         
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.