Overview  Benefits  Instructions  Void Reduction

Simplify and Speed Up QFN and LGA device placement and rework

Minimal Voiding with “Bumped” Leadless Device BEST’s patent pending StencilMate™ rework stenciling process consists of either a single stencil “bumping” the pads of the part OR a part “bumping” stencil and its mate residing on the PCB which helps to guide the bumps to the correct location on the board. The stencils can be made quickly without tooling charges in almost any possible array pattern, including various pitches and ground pad configurations.

StencilMate™ rework stencils will accurately and repeatably place “bumps” on the lead-less devices requiring rework. These “bumps” stand the part up off the board at a greater distance compared to standard rework or placement techniques. This greater standoff height offers the following advantages:

• Makes the device easier to clean (See cleaning article here)
• Reduces voiding as the flux can more easily outgas (See article here)
• Allows for easier inspection as you can optically inspect underneath the device with an endoscope.

The mating StencilMate™ stencil resides permanently on the PCB site location and provides the matching “wells” for the “bumps” to align and be placed in. Users can “feel” when the “bumps” fir snugly into the stencil apertures thereby assuring alignment. This happens without the use of a high end vision system. Both methods are in the IPC 7721 repair guidelines as repair techniques.

StencilMate™ rework stencils can be used on the smallest pitch state of the art QFNS, LGAs and other lead-less package types. These stencils have been used on parts with pitches down to 0.35mm and package sizes down to 2.5 x 2.5 mm!

StencilMate™ stencils are packaged in groups of (20) in a small anti-static bag. Each packet also consists of enough stencils to “bump” (20) parts or enough StencilMate™ device / board pairs to rework (10) devices. Squeegees are sold separately.

Why StencilMate™ over other rework methods?

Other rework methods are either capital intensive, require a high degree of skill or require long lead time expensive tooling for each every pattern. Area array rework systems requiring that the part be inverted, printed using custom tooling for every package configuration and then aligned and placed are capital intensive and require programming and profiling skills. Semi automated rework systems which dispense paste on the board and then align the component are capital and programming intensive.

BEST can process your StencilMate™ stencils using its LASER machining capabilities eliminating the need for mechanical fixturing which is expensive and takes time to manufacture. There are NO tooling costs associated with any new StencilMate™ patterns ordered.

StencilMate™ lead-less device rework stencils are designed to work with your existing tool set. You can use any adequate reflow source including hot air or IR tools, area array rework system or an oven.

BEST’s StencilMate(TM) QFN stencils leave no harmful residues in place on the PCB/device after it has been taken off of the PCB or device.

The testing was performed by an outside laboratory with the following as background information:

• Blanks and controls were tested on the Dionex ICS 3000 ion chromatography system before the test began. NOTE: NIST-traceable standards for all system calibrations were used.
• A 1.5mL sample of each test samples’ extracted solution was analyzed using a 1.7mM sodium bicarbonate/1.8mM sodium carbonate eluent.
• All testing was performed on a Dionex ICS 3000 ion chromatography system using Chromeleon software.

In blind testing Group "B" represented the StencilMate(TM) samples. These samples were prepared using the StencilMate(TM)) stencil and a no clean SAC 305 solder paste alloy. The complete report can be found here.

Bumped devices for production?

BEST services group can take your lead-less devices and bump them with consistent bump, clean and bake them and send them back to you in a tape and reel format. This allows you to have the advantages of the bumped stencils for your production lots. Call us (847) 797-9250 for ore details.