PCB proofing has always been a primary concern for test engineers, ensuring effective test programs that perform well in production. “In-Circuit Test (ICT)” remains highly effective in detecting manufacturing defects. Advanced ICT systems enhance test functionality by allowing programming of Flash memory, PLD, FPGA, and EEPROM during testing. The Agilent 3070 system leads the ICT market. ICT continues to play a crucial role in PCB assembly (PCA) manufacturing and testing. However, how will the industry’s shift towards lead-free PCBs impact the ICT stage? The promotion of lead-free soldering technology has spurred extensive research into PCB surface treatment. While these studies mainly focus on technical performance during PCB construction, the influence of different surface treatment technologies on testing stages, beyond contact resistance, is often overlooked. This report will delve into observed impacts on ICT and the imperative to understand and adapt to these changes.
PCB proofing surface treatment experience and training engineers are crucial for realizing changes in the ICT PCB production process. This article focuses on lead-free PCB surface treatment, especially during the ICT stage of manufacturing. It reveals that the successful implementation of lead-free surface treatment depends significantly on the PCB fabrication process.
A successful ICT test hinges on the physical characteristics of the contact points between the test probes of the needle bed fixture and the PCB test pads. When a sharp probe touches a soldered test point, the solder can deform due to the high contact pressure of the probe exceeding the solder’s yield strength. This deformation allows the probe to penetrate any surface impurities on the test pad. Subsequently, the clean solder beneath ensures optimal contact with the test point. The depth of probe penetration directly correlates with the yield strength of the material targeted. Deeper probe insertion enhances contact quality. An 8-ounce (oz) probe can exert a contact pressure ranging from 26,000 to 160,000 pounds per square inch (psi), depending on the probe’s surface area. Given solder’s yield strength of approximately 5,000 psi, such relatively soft solder facilitates improved probe contact.
Selection of PCB proofing surface treatment processes is critical. Understanding available options and their capabilities is essential before exploring cause-and-effect relationships. All PCBs feature a copper layer prone to oxidation and damage if left unprotected. Various protective layers exist, with hot air solder leveling (HASL), organic solder protection (OSP), electroless nickel-gold immersion (ENIG), silver immersion, and tin immersion being common choices.
Hot air solder leveling (HASL) remains a primary surface treatment method in the industry, traditionally utilizing lead-tin alloys. Excess solder is removed via an “air knife,” which blows hot air across the board surface. HASL offers several advantages in PCB production, including cost-effectiveness and the ability to withstand multiple reflow soldering cycles, cleaning processes, and storage. For ICT, HASL ensures automatic solder coverage of test pads and vias. However, compared to alternative methods, HASL often falls short in surface flatness and coplanarity.
Recent years have seen the rise of lead-free HASL alternatives, gaining popularity due to environmental concerns and regulatory shifts away from lead-based processes. While traditional HASL has proven effective over time, evolving environmental regulations and the increasing complexity and finer pitch of modern boards expose its limitations. Advantages of HASL include maintaining solderability throughout the manufacturing process without adverse effects on ICT. However, disadvantages include reliance on lead-based processes, which face stringent regulatory restrictions and eventual phase-out. Furthermore, for fine pin pitches (<0.64mm), HASL may lead to solder bridging and thickness inconsistencies, while its uneven surface can pose coplanarity challenges during assembly.
In conclusion, selecting the right surface treatment technology is crucial for PCB proofing to ensure optimal performance and compliance with evolving industry standards and environmental regulations.
PCB proofing surface treatment experience and training engineers are crucial for realizing changes in the ICT PCB production process. This article focuses on lead-free PCB surface treatment, especially during the ICT stage of manufacturing. It reveals that the successful implementation of lead-free surface treatment depends significantly on the PCB fabrication process.
A successful ICT test hinges on the physical characteristics of the contact points between the test probes of the needle bed fixture and the PCB test pads. When a sharp probe touches a soldered test point, the solder can deform due to the high contact pressure of the probe exceeding the solder’s yield strength. This deformation allows the probe to penetrate any surface impurities on the test pad. Subsequently, the clean solder beneath ensures optimal contact with the test point. The depth of probe penetration directly correlates with the yield strength of the material targeted. Deeper probe insertion enhances contact quality. An 8-ounce (oz) probe can exert a contact pressure ranging from 26,000 to 160,000 pounds per square inch (psi), depending on the probe’s surface area. Given solder’s yield strength of approximately 5,000 psi, such relatively soft solder facilitates improved probe contact.
Selection of PCB proofing surface treatment processes is critical. Understanding available options and their capabilities is essential before exploring cause-and-effect relationships. All PCBs feature a copper layer prone to oxidation and damage if left unprotected. Various protective layers exist, with hot air solder leveling (HASL), organic solder protection (OSP), electroless nickel-gold immersion (ENIG), silver immersion, and tin immersion being common choices.
Hot air solder leveling (HASL) remains a primary surface treatment method in the industry, traditionally utilizing lead-tin alloys. Excess solder is removed via an “air knife,” which blows hot air across the board surface. HASL offers several advantages in PCB production, including cost-effectiveness and the ability to withstand multiple reflow soldering cycles, cleaning processes, and storage. For ICT, HASL ensures automatic solder coverage of test pads and vias. However, compared to alternative methods, HASL often falls short in surface flatness and coplanarity.
Recent years have seen the rise of lead-free HASL alternatives, gaining popularity due to environmental concerns and regulatory shifts away from lead-based processes. While traditional HASL has proven effective over time, evolving environmental regulations and the increasing complexity and finer pitch of modern boards expose its limitations. Advantages of HASL include maintaining solderability throughout the manufacturing process without adverse effects on ICT. However, disadvantages include reliance on lead-based processes, which face stringent regulatory restrictions and eventual phase-out. Furthermore, for fine pin pitches (<0.64mm), HASL may lead to solder bridging and thickness inconsistencies, while its uneven surface can pose coplanarity challenges during assembly.
In conclusion, selecting the right surface treatment technology is crucial for PCB proofing to ensure optimal performance and compliance with evolving industry standards and environmental regulations.
