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The endless pursuit of smaller packages

Posted: 15 Mar 2016 ?? ?Print Version ?Bookmark and Share

Keywords:embedded component packaging? ECP? DiP? multichip module? MCM?

The bottom and top laminates were likely built up layer-by-layer of alternating metal traces and dielectrics. The contacts to the capacitor were likely made as part of the 1st and 2nd Cu trace formation, with laser drilled via holes being made through the resin encapsulating the capacitor. These vias would have been filled together as part of the Cu metallization.

Embedding the capacitors into the FR4 substrate places them quite close to the A9 processor and this is likely being done to reduce electrical noise generated by all of the A9 transistors madly switching on and off.

TDK has taken this component embedding process one step further by embedding a silicon die into the substrate of one of its Bluetooth modules. The die can't be seen in figure 4 as it lies beneath the 32 KHz crystal oscillator, embedded in the FR4 substrate, but is seen in the package cross section, figure 5.

Figure 3: Apple A9 Package Cross Section. (Source: TechInsights' Analysis)

Figure 4: TDK Bluetooth Module. (Source: TechInsights' Analysis)

Figure 5 is a SEM cross section taken through the TDK package substrate showing a portion of the embedded Bluetooth die along with a copper strap connecting it to a copper trace on the upper FR4 type laminate. The large via seen along the left side of the image suggests that this via was opened in a two-step process, likely by laser drilling. A first laser drilling has formed the via opening over the die to expose its bond pad, and to open the wide, upper portion, of the via in the FR4 laminate. A second laser drilling process has completed the deep via opening to contact the Cu trace on the FR4 laminate.

Figure 5: TDK Bluetooth Module Cross Section. (Source: TechInsights' Analysis)

Figure 6 gives some more clues as to the fabrication sequence used to make the module. Here, we can see a thin seam along the surface of the 1st filled resin layer that lies between the die and the 1st FR4 laminate. The absence of an additional die attach layer beneath the die suggests the die was affixed to this glass filled resin while it was still in a liquid form.

We suspect that this 1st resin layer would have been cured, followed by the deposition of the 2nd glass filled resin that has encapsulated the die. The laser drilled vias described earlier would have been performed at this point, followed by what is likely to have been electro-deposited copper traces, a 3rd filled resin, and finally that attachment of the 2nd laminate structure.

Figure 6: TDK T2541 Bluetooth Module Cross Section. (Source: TechInsights' Analysis)

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