are countless examples of RoHS compliance vs. Pb-freecapability. This article examines surface-mount
RoHS compliance and lead-free
capability: are they the same? Absolutely not. Though many in the industry
would say an RoHS-compliant product ensures lead-free process capability,
nothing could be further from the truth. RoHS compliance simply means that a
product or material does not contain the hazardous substances banned under the
legislation. However, just because a material is free of the RoHS list of
excluded substances doesn’t mean it can withstand processing at the elevated
temperatures of lead-free.
There are countless examples of compliance vs. capability; this article
examines surface-mount adhesives (SMAs).
adhesives have been a part of assembly for so long they’ve almost become an
afterthought. Until recently, these so-called “glues” were expected to perform
as required, and they did for the most part. Older generation materials required
a fairly high peak cure temperature of 140-150°C. But some components relied
upon in the high-volume consumer electronics market - particularly some lower
cost components - could not withstand the heat input required for adhesive cure
and, thus, reliability was compromised. This led to the engineering of SMAs
with lower cure temperatures that used a unique approach so as to enable
sufficient cured strength for maximum performance during soldering. Based on
these requirements, a new formulation was developed that maintained historical
chip bonder properties, yet allowed for a significantly lower cure temperature
- as low as 85°C. The combination of lower cure temperature, material strength
and reduced rate of temperature rise of these newer generation materials
reduced thermal shock and improved reliability, enabling in-line, automated
assembly of temperature-sensitive components.
Lower temperature cure
adhesives became the industry standard, essentially solving the dilemma of automated
processing of temperature-sensitive components and allowing reliable, in-line
surface-mount assembly for a range of devices. While there were many benefits
of these materials, the advent of lead-free manufacturing pushed them to their
performance limits. It soon became clear that yet another adhesive innovation
would be required to meet the demands of lead-free process conditions.
With years of Pb-free research behind them, materials scientists at Henkel
worked to develop an adhesive that maintained low-temperature cure yet could
withstand the elevated process temperatures of lead free. Henkel’s
next-generation SMA, Loctite®
3629, delivers the
capabilities of previous low-temperature-cure adhesives, but is capable of
retaining its strength during high-temperature soldering processes. The SMA’s
advanced formulation maintains the benefits of lower energy input for cure, but
also has lower yield points. This enables faster dispensing and printing
ability, and results in higher adhesive strength, which can handle the extreme
temperatures of lead--free and the pull imposed on components resulting from
the greater surface tension of lead-free alloys.
RoHS Compliant and Pb-Free Capable: The Best of Both Worlds
Many SMA suppliers say their
“RoHS-compliant” materials are ideal for lead-free manufacturing. But, with
several of these products not able to tolerate the higher temperatures,
components can pop off of the PCB during reflow due to insufficient adhesion
Loctite 3629 provides both RoHS compliance and lead-free capability. Free of
the legislation’s banned substances, the SMA meets the stringent criteria and
delivers robust performance within a high-temperature environment, all while
still imparting lower temperature cure (110°-120°C). Its lead-free capability
and low temperature cure also makes Loctite 3629 environmentally friendly,
requiring much less energy for processing as compared to competitive materials.
Furthermore, its chemistry delivers both long shelf life and an extended floor
life, which is particularly beneficial in hot climates because the material
maintains its stability even after removal from refrigeration.
The SMA’s advantages are made more profound by its lead-free capability. This
material offers the best of both worlds - complete RoHS compliance and
lead-free process performance. Remember, these two features are not one and the
For more information, e-mail email@example.com or
phone (949) 789-2500.