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The Care and Handling of PTFE Laminates
A lot of attention has been given to the processing of Polytetrafluoroethylene
(PTFE) based substrates. However, not much has ever been mentioned about
the care and handling of these materials while being processed. The following
is a background on PTFE and a few tips and considerations to be given to the
treatment of PTFE substrates.
PTFE is a thermoplastic material which is very stable electrically and chemically
when compared with common thermosetting resins such as epoxy,
polyphenyleneoxide, polyimide and cyanate ester. Part of what gives PTFE its
superior performance over frequency and temperature also makes the pure
resin fairly soft. It is for this reason that all Taconic laminates are reinforced
with glass fabric.
The founder of Taconic helped develop the process for coating woven glass
fabric with PTFE resin while working for DuPont in the mid 1950’s. It is this
PTFE coated glass fabric which is the building block in the manufacturing of
our copper clad laminates. Glass fabric reinforcement of the substrate greatly
increases stability in the X and Y axis over non-woven or unreinforced PTFE
products. While the glass fabric provides excellent dimensional stability, the
following process and handling precautions should be taken to prevent
damage or deformation of the laminate during fabrication.
Do not mechanically scrub the material
As with thin core or flexible substrates, mechanically scrubbing will stretch and
deform the material. The pinch rollers used to secure the panel during
scrubbing will also cause dents as particle or brush material are pressed into
the surface of the laminate. Chemical cleaning is much preferred.
Do not pick up a panel horizontally by one end or edge
By allowing the material to flop over you may stretch the copper and
substrate. Lift the panel by two parallel edges; preferably the two
closest dimensionally.
Prevent contaminant deposits on the material or copper
The use of clean protective gloves and slip sheets will prevent contamination
and staining. You will not need to remove oils, grease or fingerprints if you
don’t deposit them.
Do not mechanically abrade the PTFE surface
If left undisturbed, the PTFE surface is excellent for adhesion of solder mask,
pre-preg and bonding adhesive without further preparation. The etched
surface of the PTFE is very wettable due to the rough tooth structure left
behind after cooper removal.
Do not stack panels directly on top of each other
Particles or debris on the surface of the panel can become imprinted into the
copper and substrate of adjacent panels. The preferred method of storage is
to rack the panels vertically. If panels must be stacked use clean, soft, slip
sheet material between each panel and keep stack height to a minimum.
Use chemical cleaning process instead of mechanical scrubbing
Eliminating mechanical cleaning and unnecessary handling will improve the
dimensional accuracy of subsequent processes by preventing mechanical
distortion of the laminate.
Eliminate the need for deburring
By adjusting drilling feeds, speeds, retract rates, foot pressure and by using
suitable entry/ backup material and drill bits, you can eliminate the need to
scrub, sand or debur the panels. Call Taconic for more information.
As with any laminate material, handling is one of the most important steps in
processing and one of the most overlooked. Improvements in the general
handling of all materials in process can potentially reduce or eliminate costly
subsequent operations such as rework, inspection and most important of all
scrap.
Following these general guidelines will answer most of the concerns
encountered when handling PTFE laminates during fabrication.
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