Technical Library | 2013-12-27 10:39:21.0
The head-in-pillow defect has become a relatively common failure mode in the industry since the implementation of Pb-free technologies, generating much concern. A head-in-pillow defect is the incomplete wetting of the entire solder joint of a Ball-Grid Array (BGA), Chip-Scale Package (CSP), or even a Package-On-Package (PoP) and is characterized as a process anomaly, where the solder paste and BGA ball both reflow but do not coalesce. When looking at a cross-section, it actually looks like a head has pressed into a soft pillow. There are two main sources of head-in-pillow defects: poor wetting and PWB or package warpage. Poor wetting can result from a variety of sources, such as solder ball oxidation, an inappropriate thermal reflow profile or poor fluxing action. This paper addresses the three sources or contributing issues (supply, process & material) of the head-in-pillow defects. It will thoroughly review these three issues and how they relate to result in head-in pillow defects. In addition, a head-in-pillow elimination plan will be presented with real life examples will be to illustrate these head-in-pillow solutions.
Technical Library | 2015-12-31 15:19:28.0
Today's consumer electronic product are characterized by miniatuization, portability and light weight with high performance, especially for 3G mobile products. In the future more fine pitch CSPs (0.4mm) component will be required. However, the product reliability has been a big challenge with the fine pitch CSP. Firstly, the fine pitch CSPs are with smaller solder balls of 0.25mm diameter or even smaller. The small solder ball and pad size do weaken the solder connection and the adhesion of the pad and substrate, thus the pad will peel off easily from the PCB substrate. In addition, miniature solder joint reduce the strength during mechanical vibration, thermal shock, fatigue failure, etc. Secondly, applying sufficient solder paste evenly on the small pad of the CSP is difficult because stencil opening is only 0.25mm or less. This issue can be solved using the high end type of stencil such as Electroforming which will increase the cost.
Technical Library | 2016-01-21 16:52:27.0
Solder paste has long been viewed as "black magic". This "black magic" can easily be dispelled through a solder paste evaluation. Unfortunately, solder paste evaluation can be a challenge for electronic assemblers. Interrupting the production schedule to perform an evaluation is usually the first hurdle. Choosing the solder paste properties to test is simple, but testing for these properties can be difficult. Special equipment or materials may be required depending upon the tests that are chosen. Once the testing is complete, how does one make the decision to choose a solder paste? Is the decision based on gut feel or hard data?This paper presents a process for evaluating solder pastes using a variety of methods. These methods are quick to run and are challenging, revealing the strengths and weaknesses of solder pastes. Methods detailed in this paper include: print volume, stencil life, response to pause, open time, tack force over time, wetting, solder balling, graping, voiding, accelerated aging, and others.
Technical Library | 2021-04-21 15:10:16.0
Voids affect the thermal characteristics and mechanical properties of a solder joint, thereby affecting the reliability of the solder interconnect. The automotive sector in particular is requiring the mitigation of solder voids in various electronic control modules to the minimum possible level. Earlier research efforts performed to decrease voids involved varying the reflow profile, paste deposit, paste alloy composition, stencil aperture, and thickness. Due to the various advantages they offer, the use of Ball Grid Array packages is common across all industry sectors. They are also prone to process voiding issues. This study was performed to determine if vacuum assisted reflow process can help alleviate the voids in area array solder joints. Test parameters in this study largely focused on vacuum pressure level and vacuum dwell time.
Technical Library | 2022-10-31 18:35:40.0
Voids affect the thermal characteristics and mechanical properties of a solder joint, thereby affecting the reliability of the solder interconnect. The automotive sector in particular is requiring the mitigation of solder voids in various electronic control modules to the minimum possible level. Earlier research efforts performed to decrease voids involved varying the reflow profile, paste deposit, paste alloy composition, stencil aperture, and thickness. Due to the various advantages they offer, the use of Ball Grid Array packages is common across all industry sectors. They are also prone to process voiding issues. This study was performed to determine if vacuum assisted reflow process can help alleviate the voids in area array solder joints. Test parameters in this study largely focused on vacuum pressure level and vacuum dwell time.
Technical Library | 2019-08-14 22:20:55.0
Cleanliness is a product of design, including component density, standoff height and the cleaning equipment’s ability to deliver the cleaning agent to the source of residue. The presence of manufacturing process soil, such as flux residue, incompletely activated flux, incompletely cured solder masks, debris from handling and processing fixtures, and incomplete removal of cleaning fluids can hinder the functional lifetime of the product. Contaminates trapped under a component are more problematic to failure. Advanced test methods are needed to obtain "objective evidence" for removing flux residues under leadless components.Cleaning process performance is a function of cleaning capacity and defined cleanliness. Cleaning performance can be influenced by the PCB design, cleaning material, cleaning machine, reflow conditions and a wide range of process parameters.This research project is designed to study visual flux residues trapped under the bottom termination of leadless components. This paper will research a non-destructive visual method that can be used to study the cleanability of solder pastes, cleaning material effectiveness for the soil, cleaning machine effectiveness and process parameters needed to render a clean part.
Technical Library | 2015-02-12 16:57:56.0
Electronic systems are known to be affected by the environmental and mechanical conditions, such as humidity, temperature, thermal shocks and vibration. These adverse environmental operating conditions, with time, could degrade the mechanical efficiency of the system and might lead to catastrophic failures.The aim of this study is to investigate the mechanical integrity of lead-free ball grid array (BGA) solder joints subjected to isothermal ageing at 150°C for up to 1000 hours. Upon ageing at 150°C the Sn-3.5Ag solder alloy initially age-softened for up to 200 hours. This behaviour was linked to the coarsening of grains. When aged beyond 200 hours the shear strength was found to increase up to 400 hours. This age-hardening was correlated with precipitation of hard Ag3Sn particles in Sn matrix. Further ageing resulted in gradual decrease in shear strength. This can be explained as the combined effect of precipitation coarsening and growth of intermetallic layer. The fractured surfaces of the broken solder balls were also investigated under a Scanning Electron Microscope. The shear failures were generally due to ductile fractures in bulk solders irrespective of the ageing time.
Technical Library | 2022-10-31 17:09:04.0
The global transition to lead-free (Pb-free) electronics has led component and equipment manufacturers to transform their tin–lead (SnPb) processes to Pb-free. At the same time, Pb-free legislation has granted exemptions for some products whose applications require high long-term reliability. However, due to a reduction in the availability of SnPb components, compatibility concerns can arise if Pb-free components have to be utilized in a SnPb assembly. This compatibility situation of attaching a Pb-free component in a SnPb assembly is generally termed "backward compatibility." This paper presents the results of microstructural analysis of mixed solder joints which are formed by attaching Pb-free solder balls (SnAgCu) of a ball-grid-array component using SnPb paste. The experiment evaluates the Pb phase coarsening in bulk solder microstructure and the study of intermetallic compounds formed at the interface between the solder and the copper pad.
Technical Library | 2015-02-19 16:54:34.0
Pad cratering is an important failure mode besides crack of solder joint as it’ll pass the regular test but have impact on the long term reliability of the product. A new pin pull test method with solder ball attached and positioning the test board at an angle of 30º is employed to study the strength of pad cratering. This new method clearly reveals the failure mechanism. And a proper way to interpret the finite element analysis (FEA) result is discussed. Impact of pad dimension, width and angle of copper trace on the strength is included. Some findings not included in previous research could help to guide the design for better performance
Technical Library | 2016-05-30 22:24:00.0
As a part of series of studies on X-Ray inspection technology to quantify solder defects in BGA balls, we have conducted inspection of 3 level POP package by using a new AXI that capable of 3D-CT imaging. The new results are compared with the results of earlier AXI measurements. It is found that 3D measurements offer better defect inspection quality, lower false call and escapes.
