Below is a list of some of the most frequently asked questions with answers.

Q1. Can the X35-186H-1 (two component) adhesion be improved with adhesion promoter
A1: The X-35-186H-1 has excellent adhesion characteristics to glass, metals and ceramics, and there is no need to add any adhesion promoter to this.

Q2. Can PMC be changed from 150C to 175C to decrease time?
A2:Yes, most probably 1hr would be OK at 175 degree C. We can provide data to support this.

Q3. Is there a significant effect for thickness differences between say 50um and a few milimeters?
A3:Most basic material performances don’t depend on the thickness.

Q4. What is the acceptable mixing ratio error allowed? (ie. 10:0.9 – 10:1.1)
A4: The acceptable error is +/- 2%, so 10 : 0.98 ~ 1.02 is the acceptable range

Q5: What is the pot-life of X35-186H-1?
A5: Shin-Etsu define potlife as being the time at 23°C at which viscosity increases more than 20%. 16 hrs is the specification.

Q6: Can the materials be supplied in pellets form?
A1: No. The compression molding materials are supplied in liquid form.

Q7: What is the required curing time on the molding machine & what is the full curing cycle
A7: The general starting recommendation is 90s @ 180C on the machine followed by 4 hours @ 150C post mold curing.

Q8: Are LPS 5547 & 5538 suitable for Metal Lead Frame molding – transfer or compression molding?
A3: Yes, the LPS-5547 and LPS-5538 are suitable for Metal Leadframes and compression molding. Neither material is suitable or can be used in transfer molding.

Q9: In case it comes only in liquid form – please advise for suitable mass production systems that are build for injection of pre-mixed molding material
A9: We have extensive experience and relationships with both TOWA and ASM for compression molding these silicones for LED devices, but we can support these activities with other suppliers also.

Q10: What about adhesion of LPS-5547 & LPS-5538 to Chips, Ceramics, Glass and other polymers
A10: Both the LPS-5547 and LPS-5538 have excellent adhesion characteristics to glass, metals and ceramics, and there is no need to add any adhesion promoter to this. As far as other polymers are concerned, these need to be tested on a case-by-case basis.

Q11: Are there materials that are suitable for transfer molding?
A11: Yes, Shin-Etsu have developed a line of highly reflective SWC transfer mold silicones for use as the reflector of the LED. These materials are transfer molded, but due to their highly complex and peculiar processing conditions, Shin-Etsu have taken this process in house and have agreed to supply the SWC ONLY as a premolded packages. These packages (known as “Tiger Leadframes” can be either metal leadframe, PCB or ceramic.

This list will be updated as questions are asked and data becomes available.

For more information regarding Shin-Etsu X35-186H-1 or any other Shin-Etsu silicone for LED assembly, please visit us or contact us for more details.

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CAPLINQ is proud to support Shin-Etsu in this highly specilized product line which uses traditional semiconductor industry transfer mold equipment to premold SWC grade silicone onto preplated leadframes (PPF). These premolded, preplated “Tiger” leadframes aim to completely replace the industry’s current PPA premolded package or substrate with a superior, cost-effective solution that can withstand high temperature and long-term UV exposure for LED and solar cell manufacturers.

Starting in 2010, Shin-Etsu plan to fully commercialize and sell these turn-key premolded leadframes that can withstand the much tougher requirements of high power LED applications and solar cell packages. Typically, ceramic packages have been considered as the only viable alternative to the industry standard PPA premolded plastic housings to withstand higher temperature and UV conditions.

For more information regarding Shin-Etsu premolded “Tiger” LF” leadframes, please visit us or contact us for more details.

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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 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.

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In short, there are four proven ways to achieve this:

• Dummy-Die silicon interposer (a space-consuming, expensive and redundant method not discussed here as it is a mature technology)
• Spacer-filled (PMMA) pastes
• Dicing Die-Attach Film (DDAF)
• Wafer Back Side Lamination (WBL)

Ways to stack same-size dies

Spacer-filled (PMMA) pastes:
The spacer-filled pastes, do work, and PMMA is OK at the higher temperatures. The point is that the PMMA spacers hold the bondline – and prevents it from collapsing under the weight of the subsequent die. In my experience, it should not be used to define the bondline thickness – the bondline thickness should be set by the die-placement machine. Should the die-placement tool come in contact with one or two spacers (as there is always a slight distribution in spacer sizes), it will compress the PMMA quite easily and the remainder of the spacers will support the die during subsequent die placements.

Although I am quite familiar with this process, I don’t believe it is the future as the die paste write pattern (ie. a snowflake design is the best pattern) is still a bottleneck in the process, and each die requires a paste dispense and must still be placed individually. Furthermore, the total Cost of Ownership (COI) of the PMMA-filled spacer-pastes is definitely more expensive than either of the other two options.

Dicing Die-Attach Film (DDAF):
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.

Historically, die-attach companies are experts in the understanding, design and formulation of the adhesive portion – the die attach paste, glue or adhesive. The latest technology of 2nd generation epoxies, bismaleimides, PEAM-based adhesives, and hybrids of these chemistries pushes the limits of previous technology epoxies to achieve previously unachievable JEDEC and reliability levels. The market leaders in these areas are Ablestik (now part of Henkel) and Hitachi – which together make up more than 75% of the organic die attach market. The problem with these companies is that they have no filming expertise or experience, so they have to go externally to work with a partner to develop this.

On the other hand are the Wafer Dicing Film companies whom have a long experience and history with film, tapes and the filming process. What they possess in filming and taping capabilities, they lack in die-attach chemistry know-how. Most wafer dicing tape manufacturers propose a 1st generation epoxy-based DDAF solution, and as noted above, leading-technology die-attach pastes use new technologies and hybrid chemistries to achieve higher JEDEC levels. Furthermore, wafer dicing tape companies are historically only familiar with non-conductive die-attach adhesives, but the conductive die-attach pastes today represent the larger and bigger potential of the market as a whole. Wafer Dicing Tape companies will need to cover a lot of ground if they hope to develop this market on their own. The winner of this new DDAF market is far from clear.

CAPLINQ can now propose its AWD120 which is a non-UV Dicing Die Attach Film (DDAF) which is used for same-size die stacking as well as to remove bottlenecks from existing die-attach processes. This product is a non-conductive die attach material suitable for back-side lamination onto the wafer, but as of today, it is only available in 20µm thicknesses – so we cannot today offer the 75µm film needed to ensure enough wirebond-loop height for same-size die stacking. I will write again when we will be able to offer such a product.

Wafer Backside Coating (WBC) or Lamination:
Wafer Backside Coating (WBC) with B-stage technology is another worthy approach which, though sub-optimizing the process by still requiring two distinct materials: Wafer Dicing Tape and Die-Attach Paste, at least keeps the experts in their respective fields. For this product, CAPLINQ represents, sells and promotes Shin-Etsu Chemical SFX-513S wafer backside coating die attach material. This non-conductive, B-stage die-attach is an epoxy-silicone chemistry hybrid which B-stages in 10 mins @ 120°C and is then stable at 25°C for up to 6 months.

With the standard filler loading, it has a Young’s Modulus (E) of 1.8 GPa (1800 MPa) at 25°C and retains 50 – 80MPa at 150°C, which is high enough for the subsequent wire bonding process. It has passed MSL1 260°C and is currently in production with a number of large memory manufacturers. A technical presentation of the SFX-513S is available by contacting us.

For more information of UL classification or polyimide tapes, please visit us or contact us for more details.

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KJR-4013E is a flexible, moisture-cure silicone most often used as junction-coating resins in the manufacture of diodes. KJR-651E, KJR-655E and KJR-657E are rigid thermoset polyimide-silicones used as junction coating resins in the manufacture of higher power diodes and thyristors. Both are used due to their excellent adhesion to epoxy molding compounds (EMC), high humidity resistance, and excellent volume resistivity and dielectric breakdown properties.

To be able to conduct failure analysis, customers have asked if there is a process to remove the cured silicone / polyimide-silicone from the diodes and/or thyristors (decap).

One recommendation is to use sulphuric acid (H2SO4) which can normally clearly strip organic compounds.  Nitric acid (HNO3) is another option.  If the dissolving rate is slow, adding heat to the process helps very much.  Of course, for either of these processes, a fume hood is necessary all the time.

For more information of copper wire bonding, visit us or contact us for more details.

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Our standard cure schedule recommendation for the Shin-Etsu KJR-651E is as follows:
150°C for 1hr + 200°C for 1hr + 250°C for 4 hrs

This is the minimum cycle required to drive out the solvents and get good cure characteristics.  However, this is only a recommendation; a good starting point.

Some manufacturers use a hotter, longer cure cycle such as :
110°C for 1hr + 200°C for 1hr + 250°C for 8hrs + 300°C for 4hrs + 380°C for 30 mins.

It has been determined by them that this is optimum cure cycle required to maximize performance and minimize current leak.  This has been confirmed by several customers who measure the gate leakage or leakage current at the maximum temperature of the junction test when the reverse voltage is applied.

These two cure conditions likely (but not definitely) represent the two extremes in cure conditions that customer could use to test the performance of their parts – especially to test for gate leakage at high temperatures.  Though the higher temperature may give better gate leakage parameters, the standard may give better adhesion characteristics.  Either way, these parameters ultimately need to be tested by the customer, ultimately testing both the adhesion characteristics and leakage current at the max temperature of the junction test.

For more information, please visit us or contact us for more details.

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Shin-Etsu offer a range of silicone materials suitable for optical fiber coating.

Depending on the equipment and method of polymerization (UV Cure of Heat Cure), different categories of products are available. Refer to the figure below.

Primary Coating Material

For the primary coating, there is one heat-cure product (OF-182), and two UV-cure products (OF-211 and OF-212). These products exhibit specific optical properties as the light (data) travels through this layer. For these applications a refractive index of 1.49 – 1.52 is required and all these products have refractive indices that fall in this range.

Buffer Coating Material

The buffer coating material is used to keep the light (data) within the fiber core and thus requires a material with a much lower refractive index, typically in the 1.41 – 1.44 range. For this application, there are two heat cure products (OF-101 and OF-180) and two UV-cure products (OF-207 and OF-208).

These materials are suitable for normal telecon fibers coated with 400µm – 500µm thicknesses at line speeds of 100 to 500 m/min.

For more information on these or other products, please visit us or contact us for more details.

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