Papers about tombstoning
by Ed Briggs , Dr. Ronald C. Lasky
Chinese version of Best Practices Reflow Profiling for
Lead-Free SMT Assembly.
CHINESE LANGUAGE, graping, head-in-pillow, Voids, solder balling, solder beading, tombstoning, reflow profile, solder defects
[Permanent Link to this Paper ]
Posted on 22 Mar 2010
by Dr. Ronald C. Lasky , Ed Briggs
The combination of higher lead-free process temperatures, smaller print deposits, and temperature restraints on electrical components has created difficult challenges in optimizing the reflow process. Not only are the electronic components and the PWB at risk, but the ability to achieve a robust solder joint becomes difficult, especially if the PCB is thermally massive. In addition, the constant miniaturization of electronic components, hence smaller solder paste deposits, may require the use of smaller particle-sized powders. Both the small solder paste deposits and small particle size result in a large surface area-to-volume ratio that challenges the solder paste's flux to effectively perform its fluxing action. The possible resulting surface oxidation can lead to voiding, graping, head-in-pillow, and other defects. Smaller components are also more susceptible to tombstoning and defects related to solder paste slump.
This paper is a summary of best practices in optimizing the reflow process to meet these challenges of higher reflow temperatures, smaller print deposits, decreased powder particle size, and their affect on the reflow process. It also discusses trouble-shooting of the most common defects in lead-free reflow, such as tombstoning, solder beading/balling, residue discoloration, voiding, graping, and head in pillow.
solder defects, reflow profile, tombstoning, solder beading, solder balling, Voids, head-in-pillow, graping
[Permanent Link to this Paper ]
Posted on 1 Jun 2009
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Tombstoning of SnAgCu is affected by the solder composition. At vapor phase soldering, both wetting force and wetting time at a temperature well above the melting point have no correlation with the tombstoning behavior. Since tombstoning is caused by unbalanced wetting force, the results suggest that the tombstoning maybe dictated by the wetting at the onset of paste melting stage. A maximal tombstoning rate is observed at 95.5Sn3.5Ag1Cu. The tombstoning rate decreases with increasing deviation in Ag content from this composition. DSC study indicates that this is mainly due to the increasing presence of pasty phase in the solders, which is expected to result in a slower wetting speed at the onset of solder paste melting stage. Surface tension plays a minor role, with lower surface tension correlates with a higher tombstoning rate. SnAgCu composition with a Ag content lower than 3.5%, such as 2.5Ag, is more favorable in terms of reducing tombstoning rate with minimal risk of forming AgSn intermetallic platelet.
pb-free, tombstoning, solder, soldering, solder paste, flux, lead-free, surface mount
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Effect of solder alloy composition and properties on tombstoning of SnAgCu has been investigated. Both wetting force and wetting time at a temperature will above the melting point have no correlation with the tombstoning behavior observed at vapor phase soldering. Since tombstoning is caused by unbalanced wetting force, this unbalanced wetting force may occur at the onset of melting DSC study indicates that the tombstoning rate decreases with increasing pasty temperature range and increasing mass fraction of solid in solder at onset of melting. This slower wetting in turn results in a more balanced wetting force and accordingly reduces the tombstoning. The mass fraction of solid may be the more essential factor. Surface tension also plays a role, with lower surface tension correlates with a higher tombstoning rate. Tombstoning of SnAgCu can be regulated by the solder composition. A maximal tombstoning rate is observed a 95.5Sn3.5Ag1Cu. The tombstoning rate decreases with increasing deviation in Ag content from this composition, particularly toward the end of lower Ag content. SnAgCu composition with a Ag content lower than 3.5%, such as 2.5Ag, is more favorable in terms of reducing tombstoning rate with minimal risk of forming Ag3SN intermetallic platelet.
tombstoning, solder, soldering, solder paste, flux, lead-free, surface mount, pb-free
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Tombstoning has plagued the surface mount assembly industry for decades. While the problem seemed under control, it has begun creeping in again due to the miniaturization of discretes such as 0402S and 0201S. This article studies tombstoning behavior on a series of SN AG CU Lead-Free Solders and attempts to find a way to control the problem.
lead-free, pb-free, tombstoning, solder, solder paste, SMT, solder alloy, pasty range, soldering, reflow
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
Reflow soldering of solder paste is the primary interconnection method used in SMT assembly process. The major issues which plague the reflow soldering performance include, but not limited to, bottom-side-component-holding, bridging, dewetting, low-residue, opening, solder balling, solder beading, solder-fillet-lifting, tombstoning, defective balling for BGA, and voiding. The mechanisms, causes, and cures for each issue are briefly discussed in this article.
lead-free, soldering, solder paste, SMT, bridging, dewetting, opening, solder balling, solder beading, solder-fillet-lifting, tombstoning, balling for BGA, voiding, pb-free, reflow
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee , Gregory Evans
This paper focuses on many of the problems facing process engineers today. The experiments used in this study were designed to find the true causes of the problems and headaches which plague SMT assembly today. Data indicate that wicking is caused by a relative hotter component and is aggravated by non-coplanarity. It can be reduced by slower heating rate or more bottom-side heating. Bridging is caused by slumping, and is aggravated by smaller pitch dimension and slower flux wetting speed. Tombstoning is a result of uneven heating. It can be reduced by optimizing pads spacing and by using fluxes with slower wetting speed, or by a smaller print thickness. Problems such as slumping, clogging, solder balls, and white residue are also discussed.
lead-free, pb-free, white residue, solder balling, tombstoning, bridging, wicking, clogging, slumping, SMT, solder paste
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
