Frequently Asked Questions
Q: Do paste containers require a certain
orientation during storage?
A: Yes. Syringes and cartridges should be stored
vertically with tips facing down. Jars should be
stored right side up.
Q: Does solder paste require refrigeration?
A: Suggested storage temperature for paste is
between 40°F and 70°F (4°C to 21°C). If ambient
conditions are outside this temperature range, then
refrigeration is required.
Q: What is the shelf life of solder paste?
A: At a minimum, six months from date of
shipment when stored as recommended. Paste
should not be frozen. Warmer conditions will
reduce shelf life and/or cause flux separation. The
end user needs to determine actual shelf life if stored
outside recommendations. In this case, the
replacement guarantee is void.
Q: What happens to solder paste if it is frozen?
A: In many cases, nothing happens. However,
some pastes are susceptible to damage that impairs
paste performance. As a consequence, we
recommend not freezing any of our solder pastes and
paste fluxes. If you do “freeze” some paste, test its
performance before use on live product.
Q: Will solder paste last beyond the stated sixmonth
shelf life?
A: EFD guarantees that properly stored solder paste
will perform properly for up to 6 months from date
of shipment, or material will be replaced at no
charge. Many of our solder pastes will last well
beyond the warranty period. Customers wishing to
use “expired” paste should re-qualify the material by
running test boards or parts through the entire
production process to confirm good soldering
results.
Q: Are there telltale signs of improper storage
and/or handling?
A: Aside from poor performance, the other major
sign of mishandled solder paste is separation of the
flux and alloy particles. Solder paste should be
uniform in color and consistency.
Q: Should solder paste be used direct from
refrigeration?
A: No. Solder paste should be used at “room
temperature.” This will assure intended viscosity
and prevent potential condensation. Recommended
warm-up time is four hours.
Q: Can solder paste be warmed up quicker than
the recommended 4 hours?
A: We do not recommend it. However, if
necessary, faster warm-up may be achieved by
placing the sealed container in a water bath or
similar equipment at or near ambient temperature.
Syringes require approximately fifteen minutes
while jars and cartridges can take up to 45 minutes.
DO NOT heat paste with an oven or other
environment set above “room temperature.” Dry all
packing completely prior to use to prevent water
coming in contact with the solder paste.
Q: Should solder paste be re-refrigerated?
A: No. Solder paste should be used as needed.
Material should be left at room temperature once
removed from refrigeration. In the event that a
container of solder paste would go unused after
removal from refrigeration, and ambient temperature
exceeds 75°F (25°C) for an extended time before
use, it may be returned to cool storage.
Q: Can excess stenciling solder paste be re-used?
A: In general, we do not recommend reuse of solder
paste remaining on the stencil. However, if paste is
relatively fresh, it can be put into a jar and stored for
reuse. Never put used paste back into the same
container as new paste. This will contaminate the
unused paste and degrade its performance.
Q: I’m getting solder balls on the sides of my
chip components. How do I make them go away?
A: Solder balls on the sides of chip components are
typically referred to as “solder beads” due to their
large size. Two process changes may be possible to
minimize or eliminate the problem.
1) Aperture reductions designed to decrease the
quantity of paste trapped between the part
and board solder mask. The most effective
shape is a triangular shape removed from the
inside edge of each aperture. Two other
options in use are a home plate shape and
simple aperture reduction on the inside
edges. Call Technical Service for specifics.
2) Component placement accuracy relative to
paste is critical. Reductions all by
themselves do not guarantee elimination of
solder balls if pick & place accuracy is
inadequate. Tune your equipment to
optimize vision recognition and placement
accuracy of your chip components.
Q: What are the effects of a Nitrogen atmosphere
on solder paste reflow?
A: Four effects are more significant than others.
1) Increased surface tension of molten solder
alloy changes fillet shapes, improves part
centering, and may increase tombstoning.
2) The low oxygen content retards oxidation,
allowing for longer and hotter profiles.
3) Nitrogen transfers heat better than air so set
points may be lower.
4) Evaporation of many fluid flux constituents
is increased, thereby reducing the quantity of
flux residue.
Q: What should my no-clean residue look and
feel like?
A: No-clean residues should be colorless or nearly
so to facilitate visual inspection. They should be
tack free and fairly brittle, allowing for easy
penetration of test probes without clogging.
Q: We want to switch to lead free solder. What
do we have to worry about?
A: The issue of greatest concern is component
survivability at the higher reflow temperatures
required for lead free solder alloys. Both circuit
board materials and components have been
developed around lower temperature solders and can
be damaged when processed at lead free reflow
temperatures. Check your component specifications.
Q: Will our inspection criteria have to change?
A: Yes. Only Sn63/Pb37 has the mirror smooth,
bright finish that inspectors are typically trained to
look for. High tin, lead free alloys will look light
colored and dull or grainy in comparison. This look
is a function of the alloy crystal structure. EFD
strongly recommends retraining and requalification
of inspection and rework personnel when switching
from an Sn/Pb soldering process to a lead free
process.
Solder-paste-warm-up-machine
