Manufacturing / Production Technology, Hardware & Services


Self-aligning, Pb-free capable corner support for CSPs

14 May 2008 Manufacturing / Production Technology, Hardware & Services

While underfill materials were originally designed to accommodate for coefficient of thermal expansion (CTE) mismatches between the substrate and device, newer generation underfill systems have also found favour among manufacturers seeking to enhance drop test reliability for today's handheld and mobile devices. As the industry has transitioned to lead-free manufacturing and the resulting solder joints have shown a tendency to be more brittle than their SnPb predecessors, providing additional component protection has become imperative for robust long-term in-field performance.

Capillary flow underfills are the best solution for CSP and BGA support in handheld products like cellphones, PDAs and portable music players that have a high likelihood of being dropped. But, for other mobile products like laptops and gaming consoles that may only experience occasional vibration or dropping issues during shipping or bending during card assembly, using a Cornerbond underfill system for these applications is the most cost-effective and time-sensitive solution.

With this technology, lines of underfill material are dispensed at the four corners of the CSP or BGA pad site prior to component placement, allowing in-line processing using standard equipment, with curing taking place during normal solder reflow. But, like any process, there are some very important considerations - especially in the age of lead-free - that must be evaluated and understood before applying the technology in process.

When using Cornerbond technology, one must realise that the material will be cured during normal reflow and not post-assembly as is the case with traditional capillary flow underfills. Therefore, the materials characteristics of the Cornerbond must be compatible with normal assembly flow and, in the case of lead-free, the higher temperatures of the process.

In order for the BGA solder reflow process to perform as it should, the solder balls must be able to collapse and self-centre so that proper interconnections between the device and the board can be formed. When manufacturers attempt to use standard Chipbonder or surface mount adhesive (SMA) materials in a lead-free process to achieve Cornerbond underfill-type reliability enhancement, the results can be catastrophic. SMA materials are not designed for this purpose and, thus, can be quite detrimental.

In a lead-free reflow process, most adhesives cure before the BGA solder balls become liquidus and collapse, which normally results in poor interconnections and a high probability of solder joint opens and fractures, yielding decreased reliability or total device failure. In addition, traditional adhesives do not allow for any self-centring so if there has been slight misalignment during the placement process, device and interconnect centring on the pads cannot occur as the adhesive cures and holds the BGA in place, not allowing for any required movement for centring.

Henkel's new patented Cornerbond material, Loctite 3508, delivers the properties necessary to provide superior BGA support while enabling self-centring and proper solder sphere collapse. The unique characteristics of Loctite 3508 have been designed for lead-free compatibility and move through a standard inline assembly process, allowing for total ball collapse and providing the self-aligning materials properties necessary to compensate for slight component to pad misalignment during placement.

Loctite 3508 Cornerbond applied to a CSP assembly process
Loctite 3508 Cornerbond applied to a CSP assembly process

Loctite 3508 Cornerbond is also reworkable, which is key especially in the case of high feature cellphone boards, ultra mobile personal computers, laptops, desktops and server boards. These boards and the larger packages used to populate them are quite often more costly than those used in cell phones, PDAs, MP3 players, digital cameras and the like, so reworkability is a necessary requirement for cost-conscious manufacturers. Easy handling and storage are also advantages of the material; Loctite 3508 can be maintained in standard refrigerated storage, has exceptional stability at room temperature and a pot life of greater than 75 hours.



Credit(s)



Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

High-performance acrylic conformal coating
29 April 2020, Vepac Electronics , Manufacturing / Production Technology, Hardware & Services
Electrolube’s HPA high-performance acrylic conformal coating is specifically designed to meet the demanding requirements of applications such as the defence and aerospace industries. It is fast drying ...

Read more...
High-performance acrylic conformal coating
29 May 2020, Vepac Electronics , Manufacturing / Production Technology, Hardware & Services
Electrolube’s HPA high-performance acrylic conformal coating is specifically designed to meet the demanding requirements of applications such as the defence and aerospace industries. It is fast drying ...

Read more...
New range of thermal gap fillers
29 May 2020, Vepac Electronics , Manufacturing / Production Technology, Hardware & Services
Global electro-chemicals manufacturer, Electrolube, has introduced a versatile new range of gap-filling products with excellent thermal performance. GF400 is a two-part, liquid silicone-based gap filler, ...

Read more...
Company profile: SMTech
25 March 2020, SMTech , Manufacturing / Production Technology, Hardware & Services
It also provides a full turnkey solution, should its customers require this type of service. The company has a very modern manufacturing facility with high-speed SMT lines, automatic optical inspection, ...

Read more...
RFiber adds specialist PCB manufacturer to its stable
25 March 2020, RFiber Solutions , Manufacturing / Production Technology, Hardware & Services
RFiber Solutions recently announced the addition of Transline Technologies Inc. (TTI) to its growing portfolio of electronics and RF/microwave suppliers. “The addition of TTI adds a competitive and very ...

Read more...
Tip-heater cartridge soldering iron
25 March 2020, MyKay Tronics , Manufacturing / Production Technology, Hardware & Services
PACE Worldwide’s new TD-100A ergonomic soldering iron maintains the comfort and feel of the original TD-100 handpiece yet contains many enhancements. The TD-100A’s Cool Touch design features all-aluminium ...

Read more...
BTU supports Hermes standard
25 March 2020, MyKay Tronics , Manufacturing / Production Technology, Hardware & Services
BTU International announced that it now supports the Hermes standard, officially referred to as IPC-HERMES-9852. Hermes links individual machines together with a direct form of horizontal communication. The ...

Read more...
Soldering iron tester
25 March 2020, Vepac Electronics , Manufacturing / Production Technology, Hardware & Services
Hakko’s FG-101B is a soldering iron tester for measurement of tip temperature, leak voltage, and tip to ground resistance, for daily maintenance of a soldering station. Control of tip temperature, leak ...

Read more...
All good things come to an end
25 March 2020, Microtronix Manufacturing , Manufacturing / Production Technology, Hardware & Services
“Contract manufacturing is not for the fainthearted and my respected colleagues and competitors will attest to this.” – Mike Goodyer.

Read more...
Water-based decoating of coating frames
25 March 2020, Electronic Industry Supplies , Manufacturing / Production Technology, Hardware & Services
Its unique formulation guarantees both a high level of worker safety and very strong cleaning performance with good material compatibility – both with cleaning systems and coating frames or tools. ATRON ...

Read more...