As electronic products grow towards portability, miniaturization, networking and multiple medium, higher demands have been laid to packaging technology of multi-chip devices with new high-density package technologies constantly coming into being among which BGA (ball grid array) is the most prevalent. Through changing peripheral leads mode applied by traditional packages, BGA contains solder balls which are actually Pb/Sn solder bumped joints playing a role as leads under its base. Compared with traditional packaging mode, BGA features advantages of numerous I/O per unit area, low lead inductance and capacitance, excellent thermal dissipation and low demand of alignment, all of which leads BGA package to the mainstream of modern package technologies.
In spite of so many advantages introduced in previous paragraph, BGA package features defects as well, especially in terms of quality control during filter. This article will provide some measures on quality control of BGA components based on their properties.
Possible Abnormities of BGA Components during Filter
Possible abnormities of BGA components during filter primarily come in two types: solder balls and cover plate. The former includes solder ball damage, solder ball falling and solder ball oxidation while the latter can never be determined unless GJB548B-2005 is used as a reference.
• Solder Ball Damage and Cover Plate Scratch
Solder ball damage and cover plate scratch take place mostly as a result of mismatching with aging socket which further leads to high temperature and aging of components.
Test sockets for BGA packaging come in two types: needlepoint type and claw type. Needlepoint-type test socket features a needlepoint shape of contact method between solder balls and socket, that is, point-to-ball type. This type of socket tends to cause needle points on solder balls and needlepoint tends to become deformed after long-term application, which then cause solder ball damage. Claw-type sockets are those sockets with complete solder balls embraced in test tank. This type of sockets tend to cause abrasion which then leads bumping to take place at peripheral of solder balls due to abrasion of test tank. In one word, both needlepoint-type sockets and claw-type sockets will cause solder ball damage after long-term application.
• Solder Ball Falling
Solder ball falling belongs to an accidental phenomenon and failure often takes place at nickel-plated surface or gold-plated surface. Solder ball falling is possibly associated with pad surface such as pollution and nickel oxidation. In the process of reflow soldering, adhesion is not good between solder paste and pad, leading solder balls to fall during humidity test. Another possible reason for solder ball falling is associated with gold-plated thickness on the surface of pad because too thick gold and tin tends to generate brittle metal alloy, leading solder balls to fall.
• Solder Ball Oxidation
Solder ball oxidation seldom occurs during first filter for quality inspection on BGA-package components. The longer solder balls are exposed to the air, the more easily oxidation will take place. As a result, solder ball oxidation usually takes place in second filter process. Therefore, it's of much significance to stop solder balls from oxidation when it comes to BGA components quality control.
How to Implement Quality Control on BGA Components?
• Rigorous IQC
Visual inspection is inevitable for IQC (incoming quality control) on any component, including BGA. BGA components call for 100% inspection with soldering balls 100% inspected under microscope which is especially necessary for BGA components after second filtering because BGA components ready for second filtering go for a long time span, possibly leading soldering balls to be oxidized. Visual inspection is used to verify qualification of their appearance. Moreover, BGA components receive insufficient protection during transportational process, causing soldering ball damage and soldering ball falling.
• Process Control
Soldering ball protection is significant during the process of BGA component filtering. To better protect soldering balls from suffering from damage issues, the following measures can be made.
a. Standard Operation
BGA component standard operation principles should be formulated with BGA component field control strengthened.
1) Anti-oxidation: All BGA components and their test sockets should be placed in nitrogen cabinet during test phase to delay the oxidation of soldering balls and sockets.
2) Soldering Ball Protection: Turnover of BGA components should be done through purpose-made pallet and anti-static foam which can guarantee physical protection of BGA components during turnover.
c. Test Prototype
Sockets have to be carried out prior to each time of test with 1 to 2 samples tested to verify whether scratch takes place on cover plate and damage is available on soldering balls. When no abnormities are inspected, test can be continued. When abnormities are exposed, test can never be continued unless sockets are repaired.
d. Socket Lifetime Evaluation and Inspection
All sockets feature their own life time and quality of components will be dramatically reduced when life time is exceeded, which is why BGA component lifetime evaluation is essentially important. After sockets begin to be produced, their life time should be evaluated and inspection should be implemented before BGA component life time arrives. Test volume should be estimated before later test. Inspections have to be carried out before and after test on sockets and components to guarantee that no appearance will be caused due to issues concerning sockets.
e. Quality Control
Quality should be emphasized from the beginning. First, quality publicity and implementation and quality education should be delivered to all managers and first-line workers to ensure that all the staff can be aware of all existing issues and easily-accessible issues so that quality issues will be aroused again due to insufficient publicity and implementation. Next, training needs to be carried out to first-line workers with operations standardized to minimize quality loss due to unsuitable operations. Finally, both quality inspection and quality feedback are also necessary. Quality information statistics and quality feedback should be reported. The reported content includes data statistics, batch problems, potential quality hazards and suggestions on quality control, all of which will be provided to customers as reliable information and reference material for superior departments for their emulation of management measures.
Furthermore, internal audit and monitoring inspection should be actively carried out within quality system. Quality control has to be started from the beginning with purchase sources rigorously controlled and key links emphasized. Whenever practical issues are exposed, constant improvement measures should be maintained.
PCBCart provides full-scale and strict IQC on purchased components
Conforming to rigorous supply chain management system, PCBCart carries out full-scale and strict IQC on purchased components. Owing to more than 10 years' experience in this industry, PCBCart has maintained a long-term cooperative relationship with a large amount of authorized electronic component manufacturers and distributors. Each piece of components has to be inspected prior to authentic PCBA.
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