The flatness range of the PIN pins of SMD ICs

"The flatness of SMD IC (Surface Mount Device Integrated Circuit) pins is one of the key parameters affecting soldering quality. Excessive pin unevenness and large variations in pin pitch can easily lead to soldering issues such as solder bridging, insufficient solder joint strength, etc.

For the flatness of SMD IC pins, there is no universal absolute value. It depends on the following important factors:

Pin Pitch:

• Fine-pitch Devices: For devices with fine pitches, such as QFP (Quad Flat Package) with pitches of 0.5mm, 0.4mm, 0.3mm, or even smaller, the flatness requirement for pins is very high. The narrow gaps mean that any unevenness can cause solder bridging between adjacent pins.

• Coarse-pitch Devices: For devices with coarse pitches, such as SOIC (Small Outline Integrated Circuit) with pitches of 1.27mm (0.050 inch) or larger, the tolerance for flatness is relatively higher.

Number and Arrangement of Pins:

• Longer Leads: Longer pins are more prone to bending due to mechanical stress and temperature changes.

• Higher Pin Count: Overall flatness becomes even more critical for devices with a large number of pins.

Application Environment and Reliability Requirements:

• High-Reliability Applications: For applications like medical devices, aerospace, and military, the requirements for pin flatness are extremely stringent.

• Consumer Electronics: May have relatively relaxed standards but still need to meet basic soldering requirements.

Industry Standards and Customer Specifications:

• JEDEC (Joint Electron Device Engineering Council): This is a key organization for setting semiconductor industry standards. JEDEC has established many guidelines regarding package and pin flatness.

• IPC (Association Connecting Electronics Industries): IPC also has related standards for solder products and soldering, which may indirectly affect the requirements for pin flatness.

• Contract Manufacturer (CM) or Customer's Specific Requirements: Many large electronics manufacturers establish their own detailed technical requirements for suppliers, which include specific provisions for component pin flatness.

Common Industry Guidelines and Rules of Thumb:

While there's no single absolute value, the following are commonly referenced industry guidelines:

• For Fine-pitch Devices (e.g., 0.5mm pitch QFP):

• Maximum Allowed Warpage/Bow: Typically 0.1mm (4 mil) or lower.

• Stricter requirements may reach 0.05mm (2 mil).

• For Standard Pitch Devices (e.g., 1.27mm pitch SOIC):

• Maximum Allowed Warpage/Bow: May range from 0.15mm (6 mil) to 0.2mm (8 mil).

Definition of "Flatness":

• Usually refers to the distance from the contact point to the highest/lowest point.

• Sometimes measured as "bow" or "warp," especially when discussing the flatness of the entire device.

How to Inspect?

• Visual Inspection: For relatively larger devices and obvious issues, visual inspection can be used.

• Flatness Gauge or Air Gauge: These are more precise measurement methods, especially on production lines.

• Optical Measurement System: Automated high-precision measurement.

• Using Optical Filters or LED Lights: Placing the device between a light source and an observation plane makes it easier to see pin warpage.

Summary and Recommendations:

• Consult the Datasheet: This is the first and most authoritative step. IC manufacturers will clearly state the pin flatness requirements (usually in mm or mil) in their datasheets.

• Consult Your PCB Assembler (PCBA House): Communicate with your assembler(s) to understand their acceptance standards for pin flatness of different types of devices. They are usually more aware of the real-world production issues.

• Refer to JEDEC or IPC Standards: If the datasheet is unclear, you can refer to relevant JEDEC standards (such as JEDEC MS-002, JEDEC MO-0xx series, etc.) or relevant IPC standards.

• Small Batch Testing: If you have concerns about the flatness of a particular device, you can perform a small batch soldering test first, observe the soldering results, and then decide whether it will affect production.

Generally speaking, for surface-mount devices, pins should be as flat as possible, with the smallest deviation being better to ensure soldering reliability. For precision fine-pitch devices, 0.1mm (4 mil) is a relatively common upper limit, and lower values are more ideal