Same Size Die Stacking | Wafer Back Side Coating (WBC) Options

In the last post about Same Size Die Stack­ing Options, we dis­cussed the var­i­ous ways to do same size die stack­ing of die, a typ­i­cal con­fig­u­ra­tion for mem­o­ry die stacks that have the same dimen­sions. In this post, we would like to elab­o­rate on the Wafer Back­side Coat­ing (WBC) options for same-size die stacks.

As can be seen in the pho­to below, there are also two vari­a­tions on the Wafer Back­side Coat­ing Options also. The first fig­ure on the left, there is the “no flow over wires” option. In this option, using Shin-Etsu SFX-513S the entire back­side of the die is not coat­ed and the wire­bond­ing is either not affect­ed dur­ing place­ment of the 2nd die, or the wire­bond­ing is done in a sub­se­quent stage in the process. In the sec­ond image on the right, using either Shin-Etsu SFX-524A Shin-Etsu SFX-526Aor the Wafer Back­side Coat­ing mate­r­i­al does flow over the wires, and there­fore needs to be liq­uid enough to pass over the wires dur­ing die place­ment and not cause any wire dam­age.

Wafer Backside Coating Options for Same Size Die Stacking
Wafer Back­side Coat­ing for Same Size Die Stack­ing: SFX-513S, SFX-524A and SFX-526A

Advan­tages of No Flow Over Wire (NFOW) Tech­nique:

  • Epoxy Mold­ing Com­pound (EMC) com­plete­ly encap­su­lates the wire with no risk of Coef­fi­cient of Ther­mal Expan­sion (CTE) mis­match between Die Attach (DA) and EMC
  • Die Attach Oper­a­tion can be done sep­a­rate­ly from Wire­bond­ing

Dis­ad­van­tages of No Flow Over Wire (NFOW) Tech­nique:

  • A non-uni­form wafer back­side coat­ing is applied to each die — requir­ing sten­cil appli­ca­tion

Advan­tages of Flow Over Wire (FOW) Tech­nique:

  • A uni­form wafer back­side coat­ing is applied to each die, sten­cil print­ing or spin-coat­ing is pos­si­ble
  • Entire Wafer can be coat­ed
  • In-line process of die-attach, wire­bond­ing, die-attach, wire­bond­ing is pre­served

Dis­ad­van­tages of Flow Over Wire (FOW) Tech­nique:

  • Epoxy Mold­ing Com­pound (EMC) does not com­plete­ly encap­su­lates the wire, so there is a risk of Coef­fi­cient of Ther­mal Expan­sion (CTE) mis­match between Die Attach (DA) and EMC
  • Die Attach Oper­a­tion can be done sep­a­rate­ly from Wire­bond­ing

The dif­fer­ence between Shin-Etsu SFX-524A and Shin-Etsu SFX-526A is that Shin-Etsu SFX-524A con­tains no sol­vent and is there­fore bet­ter suit­ed for spin-coat­ing, whear­eas Shin-Etsu SFX-526A has sol­vent which helps it hold its shape bet­ter after sten­cil print­ing.

For more infor­ma­tion regard­ing Shin-Etsu Die Attach SFX-513S, Shin-Etsu SFX-524A or Shin-Etsu SFX-526A please vis­it us or con­tact us for more details.

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 “Same Size Die Stacking | Wafer Back Side Coating (WBC) Options

  1. Dic­ing Die-Attach Films (DDAF) are in my opin­ion the future of this mar­ket. The biggest chal­lenge with this prod­uct as I see it is that no sin­gle com­pa­ny pos­sess­es a long his­to­ry and expe­ri­ence with the pro­duc­tion of such a prod­uct. These prod­ucts are the result of a com­bi­na­tion of die-attach chem­istry and wafer dic­ing film capa­bil­i­ties.

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