time temperature epoxy molding compounds minimum achievable viscosity

Effects of time and temperature on molding compounds minimum achievable viscosity

Dur­ing the trans­fer mold­ing or injec­tion mold­ing process, the epoxy is exposed to ele­vat­ed tem­per­a­tures and pres­sure. At tem­per­a­ture and under pres­sure, the epoxy mold compound’s vis­cos­i­ty will drop sig­nif­i­cant­ly going from a sol­id at room tem­per­a­ture to a liq­uid when exposed to tem­per­a­tures of 160°C to 200°C under 1–2 bars of pres­sure. Unlike a ther­mo­plas­tic how­ev­er, epoxy mold­ing com­pounds are ther­moset plas­tics. This means that at con­tin­u­ous expo­sure to tem­per­a­ture, the vis­cos­i­ty will first drop to its min­i­mum achiev­able vis­cos­i­ty and then rise again as the epoxy cures until the epoxy stops flow­ing com­plete­ly. (See Fig­ure 1).

Shimadzu viscosity test and minimum achievable viscosity
Fig­ure 1. Shi­madzu vis­cos­i­ty test show­ing min­i­mum achiev­able vis­cos­i­ty

This is an impor­tant step in the mold­ing process as it allows the epoxy to flow into the mold cav­i­ties and encap­su­late the device or com­po­nent before cur­ing to pro­vide strong mechan­i­cal pro­tec­tion. Fail­ure to com­plete­ly encap­su­late the part is called “incom­plete fill”. The min­i­mum achiev­able vis­cos­i­ty can thus be impor­tant to ensure that the parts are com­plete­ly encap­su­lat­ed and that there are no cas­es of incom­plete fill.

An indus­try stan­dard test to mea­sure the vis­cos­i­ty is called a Shi­madzu vis­cos­i­ty flow test. This test mea­sures the vis­cos­i­ty of an epoxy mold­ing com­pound at a con­stant tem­per­a­ture, typ­i­cal­ly using the epoxy mold­ing tem­per­a­ture of 175°C. The curve in Fig­ure 2 shows how the min­i­mum achiev­able vis­cos­i­ty is affect­ed after expo­sure to tem­per­a­ture for extend­ed peri­ods of time.

The dif­fer­ence in min­i­mum achiev­able vis­cos­i­ty is dif­fer­ent depend­ing on the epoxy com­pound itself and the time and tem­per­a­ture that the epoxy was stored. Mea­sur­ing this flow at dif­fer­ent times and tem­per­a­tures will there­fore give you the extent of this prop­er­ty change.

Please stay tuned for the next part in this series to explore the behav­iour of epoxy mold­ing com­pounds.

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.

One thought on “Effects of time and temperature on molding compounds minimum achievable viscosity

  1. 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. So what is one to do

    All oth­er things being equal, if the

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