What is underfill material?
An underfill is a composite material made up of an epoxy polymer with significant amounts of filler. Additional components added to the underfill formulation are flow agents, adhesion promoters, and dyes. Although primarily used for flip-chip devices, underfills can also be used with ball-grid arrays (BGAs) and CSPs.
Why is underfill needed?
Why is underfill applied? Underfill provides a strong mechanical bond between the chip and the PCB’s connection, protecting the solder joints from mechanical stress. It also helps transfer heat. Underfill softens the mismatch between the coefficient of thermal expansion (CTE) between the chip and the board.
What is Reworkable underfill?
Reworkable underfill is another type of underfill that allows the faulty chips to be replaced individually. It is the key material to address the nonreworkability issue of the current flip-chip devices.
What is solder underfill?
An underfill, typically an epoxy composition, connects the chip to the board by capillary action and then is heated to cure. The underfill material provides mechanical reinforcement to the solder joints which can increase the life of the chip.
What underfill means?
1 : a rolled or forged member (as of steel) that is imperfect because of insufficient material. 2 : an incompletely filled can or container.
What is the purpose of underfill material in flip chip technology?
WHAT is UNDERFILL AND WHY is it USEFUL? Underfill is thermoset epoxies traditionally used in flip chip applications to reduce thermal stresses solder bumps experience due to coefficient of thermal expansion mismatch between a die and the organic substrate.
What is the meaning of undefiled?
: not made corrupt, impure, or unclean : not defiled : untainted, uncorrupted English undefiled …
What is overlap in welding?
Overlap. Overlap occurs when molten metal flows over the surface of the base material and then cools without fusing with the base material. A typical cause of overlap is the supply of too much weld metal due to low welding speed. Overlap in fillet welds is caused by the droop of excessive molten metal due to gravity.
What is no-flow underfill?
No-flow underfill processing uses fluxing underfills that are dispensed onto the substrate before flip chip placement. The chip is placed onto the dispensed underfill, causing squeeze flow of the material. The assembly is then reflowed and cured simultaneously in a standard solder reflow process.
How do you make an underfill Reworkable?
The first one is to add a special additive into a standard no-flow underfill formulation (underfill 0) to make it reworkable, called underfill 1. The second approach is to develop a no-flow underfill based on a new thermally degradable epoxy resin that decomposes around 240/spl deg/C, called underfill 2.
What does Unfade mean?
1 : not losing color or freshness. 2 : not losing value or effectiveness.
Who are the undefiled?
The “undefiled in the way” are the lovers of God’s Holy Word, Precept and Ways. In the journey of life, our Christian life on the road, which leads to heaven, there are those who are living without blemish or stain, upright in their course, sincerely believing the Word of God.
What can underfill be used for in BGA?
Underfill can be used for enhancing BGA reliability: shock, vibe, and thermal cycling reliability. Underfill can be also used for ruggedizing parts other than BGAs. Ex) TSOP, CSP, etc
How is underfill applied to a ball grid array?
Underfill is applied either on a corner or in a line along the edge of the BGA or micro CSP. After application, the BGA/micro CSP is heated to a temperature between 125°C and 165°C. Capillary action is used to absorb the underfill under the BGA or micro CSP.
Why do we use underfills in solder joints?
Underfill BGA – Many manufacturers use underfill BGA packaging in order to strengthen solder joints and reinforce a product’s resistance to vibration and thermal shock. Underfill WLCSP – Underfills can significantly improve the dropping performance and raise the thermal cycle performance of Wafer Level Chip Scale Packages (WLCSPs).
How long does it take to cure BGA underfill?
After application, the BGA/micro CSP is heated to a temperature between 125°C and 165°C Capillary action is used to absorb the underfill under the BGA or micro CSP The temperature is held steady until the underfill is cured, which can take anywhere from five minutes to an hour or more, depending on the encapsulant material being used