Electronics Assembly Knowledge, Vision & Wisdom
Stencil Considerations - Miniature Components
Stencil Considerations - Miniature Components
This paper outlines different approaches to printing miniature devices along with conventional SMT devices.
Production Floor

Authored By:
William E. Coleman, Ph.D.
Photo Stencil, Colorado Springs, CO, USA
,{url:'http://www.circuitinsight.com/videos/programs_final.mp4'}], clip:{autoBuffering:true, autoPlay:true, scaling:'scale' } }).ipad();
Summary
SMT Assembly is going through a challenging phase with the introduction of miniature components such as uBGA's, .3mm CSP's and 01005 passives in to the assembly process. Example assemblies are cell phones and other hand held devices driven by consumer demand for smaller devices with increased functionality.

Printing these miniature devices along with more conventional SMT devices like .5mm QFP's and 0603 and 0805 passives is a challenge. Whereas a 4mil (100 micron) or 5 mil (125 micron) thick stencil provides good paste transfer for the normal SMT devices, stencils with this thickness have very low Area Ratios for the miniature devices. For example a .3mm CSP with a 7.5 mil (190 micron) has a .47 Area Ratio for a 4 mil thick stencil.

This paper is divided into two parts outlining two different approaches to resolve this issue. Part 1 deals with a Two Print Step Stencil Process where small apertures are printed with a thin stencil thus providing acceptable Area Ratios. A second thicker stencil is used for normal SMT devices, RF Shields, and SMT connectors. This stencil has relief pockets formed on the board side of the stencils anywhere paste was printed with the first stencil.

Part 2 deals with different stencil types (technologies) and different aperture wall coatings. Stencil technologies include Laser and Electroform; Aperture Wall coatings include PTFE coatings. Aperture Wall pictures and paste print tests compare the performance of these different configurations and how they influence paste transfer for miniature devices with Area Ratios less than the standard recommended lower limit of .5. In the second case a step stencil is not necessary.
Initially Published in the SMTA Proceedings
Reader Comment

Dr. Coleman is a wealth of knowledge, that he so freely shares with the SMT community. He is to be applauded.

Art Guidi, UTZ llc
Submit A Comment

Comments are reviewed prior to posting. Please avoid discussion of pricing or recommendations for specific products. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Company


E-mail


Country


Comments


Authentication

Please type the number displayed into the box. If you receive an error, you may need to refresh the page and resubmit the information.



Related Programs
bullet Selective Printing for BGA Components
bullet Assembly Options for Handheld Products
bullet Assembling Boards with BGAs on Both Sides
bullet Problems to Look for with Crimp Terminations
bullet How to Clamp Odd Shaped Circuit Boards
bullet Assembly and Reliability Investigation of PoP
bullet Evaluation of Stencil Materials, Suppliers and Coatings
bullet What is Solder Paste Working Life on a Stencil?
bullet How To Calculate Component Standoff Height
bullet Humidity Inside Our Screen Printer
More Related Programs
About | Advertising | Contact | Directory | Directory Search | Directory Submit | Privacy | Programs | Program Search | Sponsorship | Subscribe | Terms

Circuit Insight
6 Liberty Square #2040, Boston MA 02109 USA

Jeff Ferry, Publisher | Ken Cavallaro, Editor/Business Manager

Copyright © Circuitnet LLC. All rights reserved.
A Circuitnet Media Publication