By Dr. Phil Garrou, Contributing Editor
Finishing our look at the 2016 IMAPS Conference, let’s take a look at presentations by Shinko, Yole, UCLA, Maxim and Asahi Glass.
Kyozuka of Shinko Electric discussed their i-THOP (integrated thin film high density organic package) package for mobile applications. Based on the trend of partitioning large chips into smaller functional units that are the connected on a high density SiP, Shinko sought to develop a high density (2/2 L/S) organic package for use in mobile devices. It involves the integration of thin film layers on a conventional build up PCB as shown below. Design specs and process flow are shown below.
A discussion of the “embedding resin” which was not identified indicated that materials “B” and “C” “…can be applied for this structure” since no cracks were seen after T/C testing. IFTLE worries about these choices since these materials reportedly exhibit tensile strength between 60 & 100 MPa and elongations of < 2.5%.
Azemar of Yole discussed FOWLP market and technology trends. Yole sees the fan out market splitting in the future into (1) single die applications such as baseband, power management, Rf transceivers etc and a (2) high density market exemplified by the TSMC “InFO” that include larger IO count applications such as processors. This explains the sharp jump in their market forecasts as shown below.
Subu Iyer and his group at UCLA have been taking a look at Cu-Cu thermo- compression bonding for die to substrate interconnection. Temperature, pressure, and surface roughness were examined and optimized process parameters are shown below. Oxidation of the copper surface is shown to hinder the bonding as is surface roughness. Samples with roughness of a few hundred nm could not be bonded.
Annealing at 400 C for 2 hours gave the best bonding results.
Kelkar of Maxim discussed their mold compound free fan out package which they reconstitute on a silicon wafer.
In order to avoid the issues inherent with mold compound based fan out wafers such as warpage, Maxim has developed a process based on silicon wafers. They list one of the packages attributes as “low cost” although I’m sure there are those who would disagree. The process flow is shown below.
Cavities are formed in the silicon wafer by wet etching, die are placed face up in the cavities and the remaining space filled with epoxy. RDL and ball placement follow similar to other FOWLP chips first approaches. It is shown in cross section below. The parts have passed std WLP reliability testing.
Nomura and co-workers from Asahi Glass discussed CTE controlled glasses for the minimization of thermal stresses in package formation and assembly. In order to minimize the stress induced on silicon during thermal processing glass substrate are required to be perfectly matched to silicon over the required temp range. Asahi glass claims to have developed such a glass “glass C” as shown below.
Glass C is an aluminoborosilicate composition with controlled chemical composition and thermal history. Silicon wafers bonded to this CTE matched glass show very low warpage over the required temp range.
Answer to IFTLE 313 question:
The “rock” on the right is none other than the island of Manhattan, built on a giant slab of mica schist. The photo was taken from 10k+ feet, at night, by my younger son Christopher who is a Chef in Maine. Old time IMAPS members might remember Christopher attending the IMAPS Ogonquit MCM workshops run by Jack Balde 20+ years ago.
If you swing the picture around so that the pointy end is in the top right corner, Times square is the bright area in the lower left.
An IFTLE technology tidbit is that my neighborhood (Hells kitchen which is just west of Times Square towards the Hudson river) was one of the first neighborhoods in NYC to be electrified (well before I was born). Recall Thomas Edison’s method for generating and transmitting electricity was called direct current (DC). Westinghouse Electric purchased the “polyphase” alternating current (AC) system invented by Nikola Tesla. In an AC system, transformers are used to step up, the voltage that leaves the power plant which enables electricity to travel over long-distance wires. When the electricity reaches its destination, another transformer would then step down, the voltage so that power could be used in homes and factories. There was a major commercial battle to see what technology would win.
My father told me that our neighborhood was initially fitted with the Edison DC system and ran that way through the early 1930’s before it had to be retrofitted with the less costly and more reliable Tesla system. I’m sure at the time everyone thought going with the Edison system was the safe and sensible thing to do, but sometimes it isn’t.
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