Two-Print Stencil Solutions for Flip Chip/SMT Assembly


Reading time ( words)

Mixed technology packages that have both flip chip (FC) and surface mount devices (SMD) on the same substrate are now being assembled in a normal SMT assembly process.

Instead of dipping the FC die in flux, both flux and paste are printed on the substrate. Then the FC and SMD are placed into the paste/flux with pick-and-place equipment and sent to a reflow oven where both are soldered to the substrate.

This assembly process requires a "two-print stencil" printing procedure and requires two inline stencil printing machines. Normally, flux is printed first using a thin electroform stencil (40–50 μm thick) to print flux on the FC die pads. This is referred to as the "first print stencil."

Immediately after the first print, the substrate is advanced to the second printer. The "second print stencil" is used to print solder paste for the SMDs. This stencil is normally an electroformed 75 μm thick stencil for the solder paste apertures but has a relief step pocket 50μm thick on the contact side of the stencil in the area where flux was printed with the first stencil. This relief pocket provides sufficient clearance to avoid contact with the previously printed flux.

Read The Full Article Here

Editor's Note: This article originally appeared in the February 2016 issue of SMT Magazine.

Share

Print


Suggested Items

Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser-cut SMT Stencils (Part 2)

05/08/2019 | Greg Smith, BlueRing Stencils
In the first part of this two-part article, Greg Smith talks about a study wherein a test vehicle was created to show transfer efficiency over a wide array of area ratios. Part 2 discusses the results of the experiment, including discussions of the different SEM results featuring the paste transfer efficiencies of each material, to better understand how the aperture wall surface smoothness compares to SMT stencil performance.

Impact of Stencil Foil Type on Solder Paste Transfer Efficiency for Laser-cut SMT Stencils (Part 1)

04/24/2019 | Greg Smith, BlueRing Stencils
As innovation and demand continue to drive miniaturization in electronics, manufacturers face the constant challenge of assembling smaller and smaller components with repeatable processes and high yields. Stencil printing is the first step in the PWB assembly process, and improvements to the SMT stencil can significantly improve yields, especially for more challenging miniaturized products.

Tips & Tricks: Humidity Level for Electronics Assembly

04/10/2019 | Jason Fullerton, MacDermid Alpha Electronics Solutions
Low relative humidity (RH) can allow for higher static charges to build on objects. It can also affect solder pastes, especially OR-class pastes, and this can reduce print performance and stencil life. Read on to find out what level of RH you need for your assembly facility.



Copyright © 2019 I-Connect007. All rights reserved.