Koki is recognized as a global leader in solder paste research and development. Many of the largest OEMs and EMS manufacturers in the world are using their solder paste materials. A key reason is that they have been developed specifically to address the issues that are faced in electronics manufacturing. As a key supplier for soldering materials, Koki has a staff of over 20 materials scientists and engineers developing new soldering materials based on customer requirements and needs.

Over the last few years, there has been an increase in the rate of Head-in-Pillow component soldering defects which interrupts the joining of the BGA/CSP component solder spheres with the molten solder paste during reflow. There are many reasons for this issue such as warpage issues of the component or board, ball co-planarity issues for BGA/CSP components and non-wetting of the component based on contamination or oxidation of the component coating. This issue is occuring across a broad segment of industries including consumer, telecom and military. The issue has been found to occur not only on lead-free soldered assemblies where the increased soldering temperatures may give rise to increased component/board warpage but also on tin-lead soldered assemblies.

Based on customer needs, Koki specifically investigated and developed tin-lead and lead-free solder pastes to reduce the Head-in-Pillow component soldering defect. They developed test methods to analyze the head in pillow defect not only on BGA component test vehicles but also more fundamental studies to assess solder ball interactions with the developed materials versus control solder pastes.

The Koki flux formulations developed in the anti-pillow solder pastes have higher heat resistance which do not lose their flux activation properties as quickly and quicker wetting which helps to reduce the head-in-pillow defect.

"I visited the Koki Japan facility recently where the global solder paste R & D work is carried out. I was very impressed with the experience and dedication of the researchers and the types of testing equipment used in the development of these materials,” said Jasbir Bath, Consulting engineer for Christopher Associates/Koki Solder. “Although solder paste cannot completely eliminate the head in pillow component soldering defect, it is one part of the solution to help to remove it."

Below is a list of Koki solder paste materials to choose from which are being currently being used in the industry:

Lead-free Halogen-free pastes: S3X48-M410-A (Type 3) and S3X70-M410-A (Type 5)

• Excellent Solderability and print quality
• <900 ppm Bromine
• <900 ppm Chlorine
• 01005 process compatible

Lead-free pastes: S3X48-M406-3 (Type 3) and S3X48-M406-5 (Type 3)

• Good quality of solder joints with outstanding continual printing performance

Lead-free paste: S3X48-M420 (Type 3) Low-voiding solder paste

• Specially formulated flux chemistry ensures extremely low voiding with CSPs and broad contact area components, e.g. QFNs/MLFs
• Ensures outstanding continual printability with 0.4mm/16mil pitch component applications and long stencil idle time.

Tin-lead paste SE48-M956-2 (Type 3)

• Ensures outstanding continual printability for 0.5mm/20mil and 0.4mm/16mil component pitch applications

For more information about Koki tin-lead and lead-free solder pastes, contact Martin Gershenson or Jasbir Bath at Christopher Associates by phone at (1) 714 979 7500, or by e-mail at martin@christopherweb.com or jasbir@christopherweb.com or visit the Christopher website at www.christopherweb.com or the Koki Solder website at http://www.ko-ki.co.jp