place the bumps on the bottom of the component, since
doing this manually is time-consuming and difficult to be
accomplished at an even height — even for trained
1. To get started, clean off contaminates on the lands
of the device.
2. Place the larger of the two stencils, with the part
lands properly aligned with the apertures of the
3. Squeegee solder paste into the apertures of the
stencil. Using the squeegee, scoop a little solder
paste out of the container, then starting at one side
roll solder paste into the apertures by moving the
squeegee to the opposite side of the stencil.
4. After wiping off any excess solder, reflow based on
the type of solder you are using. It is recommended
that this be done by running the assembly through a
reflow oven (toaster oven with controls will work).
However, a heat gun can also suffice.
5. Remove the stencil from the device and clean off the
part lands using isopropyl alcohol. You should see
uniform and consistent solder bumps on the lands.
6. Now, prepare the board that the device will be
placed on by using isopropyl alcohol.
7. Place the board stencil onto the PCB. We used a
StencilMate™. Once it is properly aligned, apply
pressure to the stencil to stick it in place in order to
activate the adhesive. Make sure that the apertures
line up with the lands before you do this because
once the stencil is stuck down, it cannot be removed
and reused. To make any changes after this point,
you will have to start over.
8. As before, squeegee solder paste into the stencil.
9. Place the bumped device into the stencil. Reflow again
using the same profile to reflow the solder paste.
10. Inspect the final product for any anomalies. Make
sure that the part lies flat and hasn’t been
damaged in any way by the heat. Unfortunately,
due to the nature of the leads of the component,
inspecting the underside to check for good solder
contact is difficult. Often, the only way to truly
know if it works is to test it.
When it comes to placing BGAs, the main issue you will
see is the problem of placing fine-pitched devices and
having solder joints which cannot be visibly inspected from
the solder ball to the land.
1. Clean the site using isopropyl alcohol to get rid of
any contaminants that might interfere with a good
2. Peel the adhesive backing off of the stencil.
3. Align the stencil. The most reliable way to do this is
to line up diagonally opposite corner apertures over
their corresponding lands.
4. Once you’re sure the stencil is well aligned, place the
stencil starting at one corner and slowly work
towards the opposite corner. Smooth down the
stencil afterwards to remove any air bubbles. Apply
pressure to activate the adhesive.
5. Squeegee solder paste across the top of the stencil.
Make sure paste has been rolled into all of the
6. Wipe off any excess solder paste on top of the
stencil using a lint free wipe.
7. Gently place the BGA. Make sure the balls or leads
of the component of the part are aligned with the
8. Reflow the part either using a toaster oven or a heat
9. Inspect the BGA to make sure it is level and look
under the component to ensure that none of the
solder balls are cracked or bridged in any way.
Through this series of articles, we hope you’ve acquired
a few new skills to help you in your projects. These guides
should at least provide a solid base on which to build more
advanced soldering skills, or simply to do a little rework or
repair from time to time. Regardless of what you choose to
use these skills towards, we trust you have learned
something of value. SV
SERVO 06.2015 65
Figure 10. For a part of this size, it is most likely easier to just
place it by hand rather than with tweezers.