<story><title>3M tape with anisotropic z-axis electrical conductivity</title><url>https://www.3m.com/3M/en_US/p/d/b10167835/</url></story><parent_chain><item><author>nomel</author><text>For anyone looking for the interesting numbers:&lt;p&gt;&lt;pre&gt;&lt;code&gt;    Insulation resistance: 3.4 x 1014 ohms&amp;#x2F;square

    Contact resistance: &amp;lt; 0.3 ohms

    Minimum gap: 0.4mm

    Minimum overlay area: 3.2mm^2
&lt;/code&gt;&lt;/pre&gt;
Direct link to datasheet: &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;multimedia.3m.com&amp;#x2F;mws&amp;#x2F;media&amp;#x2F;66235O&amp;#x2F;3m-electrically-conductive-adhesive-transfer-tape-9703.pdf&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;multimedia.3m.com&amp;#x2F;mws&amp;#x2F;media&amp;#x2F;66235O&amp;#x2F;3m-electrically-c...&lt;/a&gt;</text></item></parent_chain><comment><author>kurthr</author><text>What people should also know is that every single display, and that includes every single cell phone touch screen has ACF (Anisotropic Conductive Film) in them. They aren&amp;#x27;t the same contact adhesive as this 3M film, and some are moderately expensive (e.g. &amp;gt;$0.25&amp;#x2F;inch @1mm width) for those displays, which is at least comparable (&amp;gt;10%) to the display ICs attached to them.&lt;p&gt;Why is so much ACF used? Because it is the most cost effective and compact way to connect dissimilar high density connections from one substrate to another. Displays typically require thousands of connections so you&amp;#x27;re looking at linear densities of 1 contact per mil (~25um) with resistances measured in ohms (for less than 0.01mmsq). The reason that IC packages (internally wire bonded or electroplated CSP) don&amp;#x27;t use ACF is a combination of cost, self alignment (solder pulls it into place), and much lower resistance.&lt;p&gt;The way that almost all of these ACFs are made is embedding conductive beads (often spherical of controlled diameter) which can compress when the adhesive is pressed&amp;#x2F;bonded to the two substrates. If the aerial density of the beads is right, you&amp;#x27;ll only get a few beads in contact and none will short any neighboring contacts. For displays the ACF material is typically a ~25um thick B-stage epoxy, which is tacked down and then &amp;quot;snaps&amp;quot; when heated and compressed permanently pulling together the two contact regions and compressing ~10um gold coated polystyrene balls between gold &amp;quot;fingers&amp;quot; on each glass&amp;#x2F;PCB&amp;#x2F;COF&amp;#x2F;COP side after the epoxy flows.&lt;p&gt;3M tried to get into these higher end ACFs, but now it&amp;#x27;s mostly Japanese and Korean suppliers.</text></comment>
<story><title>3M tape with anisotropic z-axis electrical conductivity</title><url>https://www.3m.com/3M/en_US/p/d/b10167835/</url></story><parent_chain><item><author>nomel</author><text>For anyone looking for the interesting numbers:&lt;p&gt;&lt;pre&gt;&lt;code&gt;    Insulation resistance: 3.4 x 1014 ohms&amp;#x2F;square

    Contact resistance: &amp;lt; 0.3 ohms

    Minimum gap: 0.4mm

    Minimum overlay area: 3.2mm^2
&lt;/code&gt;&lt;/pre&gt;
Direct link to datasheet: &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;multimedia.3m.com&amp;#x2F;mws&amp;#x2F;media&amp;#x2F;66235O&amp;#x2F;3m-electrically-conductive-adhesive-transfer-tape-9703.pdf&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;multimedia.3m.com&amp;#x2F;mws&amp;#x2F;media&amp;#x2F;66235O&amp;#x2F;3m-electrically-c...&lt;/a&gt;</text></item></parent_chain><comment><author>db48x</author><text>I think you mean 3×10¹⁴ ohms&amp;#x2F;square.</text></comment>