we build boards with thermal via farms (usually under PA's,sometimes power devices) everyday. Rather than deal with the solderign issues we have them filled with non-conductive epoxy and planarized. Typically a Peters or Taiyo material and San-Ei if it needs to be overplated (bad idea but sometimes specified). At 05:47 PM 3/13/2012, Wenger, George M. wrote: >Richard, > >As usual all good points. When we design via farms under components >that require a heat transfer we design for the heat transfer to >occur through the plated area of the via barrel and we do not rely >on the vias being filled during a soldering process (wave or solder >paste on heat spreader pads beneath the components. We also go to >great lengths to design the via diameter and stencil print pattern >so that solder doesn't flow into the vias because we don't want >solder bumps on the bottom of the board to prevent good contact to >the heat sink the board is mounted to. We also don't try to fill >the vias with epoxy or solder mask or any non-conductive material >because we would probably get some on the top or bottom side land of >the via which would prevent good heat transfer into the plated copper barrel. > >Regards, >George >George M. Wenger >Senior Principal Reliability / FMA Engineer >Andrew Corporation - Wireless Network Solutions >40 Technology Drive, Warren, NJ 07059 >(908) 546-4531 Office (732) 309-8964 Mobile >E-mail: [log in to unmask] > >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. >Sent: Tuesday, March 13, 2012 8:36 PM >To: [log in to unmask] >Subject: Re: [TN] Purpose of these plated vias? > >Hold on there, Dwight! >Does the assembly drawing call out to epoxy fill those holes? Have >you considered the implications of what could go wrong if someone >were to follow your advice? >1. Loss of thermal conductivity/change in thermal performance. It >could be that the unfilled holes are required to transfer heat to >the thermistor on the opposite side of the CCA, so the thermistor >can sense the heat and the circuit can react accordingly. What >happens if you fill those holes? You insulate the back (sensor >portion) of the thermistor. >2. A change in dielectric characheristics could occur. We have no >idea how this circuit is used. >3. If the wrong epoxy is used, it may get hot and even possibly >ignite. Total catastrophic failure (automotive fire) could follow. > >Be careful what you say, the first rule is Do No Harm. > >Charlie, >Discuss this with the customer's design engineer or contract >manager. They may wish to know about issues such as flux entrapment >driving up their costs, or convey certain cleanliness or hole-fill >requirements. Have you checked the assembly drawing for the CCA? > > >________________________________________ >From: TechNet [[log in to unmask]] On Behalf Of Dwight Mattix >[[log in to unmask]] >Sent: Tuesday, March 13, 2012 4:56 PM >To: [log in to unmask] >Subject: Re: [TN] Purpose of these plated vias? > >thermal via farm > >100% fill those vias with non-conductive epoxy will fix what ails you >in this case > > >At 12:42 PM 3/13/2012, Charlie Pitarys wrote: > >I have these PCB's (mixed technology) in house, used for an automotive under > >hood application. In several spots on the board are these array of holes. On > >the A-side a smt component like a thyristor will cover up the array. > >What are these there for? > >The wave flux residue is proving tenacious to effectively clean out of every > >via. Especially with the old school cleaning tool at this account. > > > >Some of the vias are clear but some have solder filling or partially filling > >them. These are now also filled with wave flux. > >Below is a link to a picture of the array. > >http://i123.photobucket.com/albums/o319/dartfrogmts/Kyzen/A-Side00140xFCR145 > >F20min-1.jpg > > > >I'll get them clean but curious as to why these are on the board. > >Thanks in advance > > > >Charlie > > > > > > > > > >CONFIDENTIAL > >The content of this message, including any attachments, may contain > >privileged and/or confidential information proprietary to Kyzen and is > >intended only for the named addressees. If you are not the intended > >recipient, you may not disseminate, distribute or copy this email. Please > >notify the sender immediately by email if you have received this email in > >error and delete this email from your system. > > > > > > > >______________________________________________________________________ > >This email has been scanned by the Symantec Email Security.cloud service. > >For more information please contact helpdesk at x2960 or [log in to unmask] > >______________________________________________________________________ > > >______________________________________________________________________ >This email has been scanned by the Symantec Email Security.cloud service. >For more information please contact helpdesk at x2960 or [log in to unmask] >______________________________________________________________________ > >______________________________________________________________________ >This email has been scanned by the Symantec Email Security.cloud service. >For more information please contact helpdesk at x2960 or [log in to unmask] >______________________________________________________________________ > >______________________________________________________________________ >This email has been scanned by the Symantec Email Security.cloud service. >For more information please contact helpdesk at x2960 or [log in to unmask] >______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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