epoxy molding compounds variables affecting viscosity flow wire sweep

Effects of Epoxy Mold Compound Viscosity, Flow and Filler on Wire Sweep

Recent­ly, a cus­tomer com­plained that he had a hard time cor­re­lat­ing the wire bond sweep with mate­r­i­al prop­er­ties like spi­ral flow, filler con­tent, filler size, etc. He was using mold flow analy­sis to pre­dict wire sweep, but the results didn’t seem to make sense to him.

The rea­son for this is because these prop­er­ties can be mutu­al­ly exclu­sive, and com­bi­na­tions of these prop­er­ties and result in vast­ly dif­fer­ent prop­er­ties.

Let me start with a basic exam­ple to make my point. Imag­ine you have a mold com­pound that is 80% filled by weight with spher­i­cal sil­i­ca with an aver­age par­ti­cle size of 100um. If we did noth­ing else but swap out this filler a sil­i­ca nanopar­ti­cle with an aver­age par­ti­cle size of 0.1um, what would be expect in mate­r­i­al prop­er­ty dif­fer­ences?

Though both par­ti­cle sizes may pre­dict sim­i­lar wire sweep, in real­i­ty, the nanopar­ti­cle-filled mold com­pound would be so thick that it wouldn’t be able to flow at all. Epoxy mold com­pound for­mu­la­tions often have mul­ti­ple dif­fer­ent sizes (from nanopar­ti­cles to sev­er­al hun­dred microns) and shapes of filler includ­ing spher­i­cal, angu­lar and oth­er. These com­bi­na­tions are done exact­ly to opti­mize pack­ing den­si­ty, vis­cos­i­ty and flow.

Like­wise, spi­ral flow itself is not a mea­sure of vis­cos­i­ty. It is a mea­sure of, well… flow. Spi­ral flow mea­sures the dis­tance a mold com­pound will flow when exposed to mold tem­per­a­ture and pres­sure. All oth­er things being equal, a mate­r­i­al with a low­er vis­cos­i­ty will flow fur­ther than one with a high­er vis­cos­i­ty. But all things are rarely equal. If the low vis­cos­i­ty mate­r­i­al has a short­er gel time, than it may flow fur­ther while it is still liq­uid, but will stop flow­ing soon­er than the mate­r­i­al with the longer gel time.

Epoxy mold­ing com­pound for­mu­la­tion is cer­tain­ly as much of an art as a sci­ence. Add epoxy mold con­fig­u­ra­tion, part geom­e­try, lay­out and part-count to the com­plex­i­ty and the puz­zle becomes even more com­plex. So what is an engi­neer to do when con­front­ed with this infor­ma­tion? The short answer is col­lect infor­ma­tion and test.

What data should be collected?

Start by col­lect­ing the fol­low­ing data on the epoxy mold­ing com­pound:

  • Spi­ral Flow
  • Gel Time
  • Filler Type
  • Filler Size
  • Filler Shape
  • Vis­cos­i­ty

Once you have this, ask the epoxy mold com­pound man­u­fac­tur­er to explain the trade-offs made in each of the for­mu­la­tions and then ask for sam­ples to test based on your require­ments.

Please vis­it us at www.caplinq.com to learn more about our whole range of epoxy mold com­pounds includ­ing our Trans­fer Mold Epoxy Com­pounds and our Com­pres­sion Mold Epoxy Com­pounds. If you have any oth­er ques­tions about how to process and cure epoxy mold­ing com­pounds please feel free to leave a com­ment below or don’t hes­i­tate to con­tact us.

About Chris Perabo

Chris is an energetic and enthusiastic engineer and entrepreneur. He is always interested in taking highly technical subjects and distilling these to their essence so that even the layman can understand. He loves to get into the technical details of an issue and then understand how it can be useful for specific customers and applications. Chris is currently the Director of Business Development at CAPLINQ.

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