PCBA Manufacturing Process Specification: SPI Solder Paste Inspection

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• Cited Standards

No.	Document No.	Document Title
1	IPC-7525	Stencil Design Guidelines
2	IPC-7527	Solder Paste Printing Requirements
3	IPC/EIA J-STD-004	Flux Requirements
4	IPC/EIA J-STD-005	Solder Paste Requirements
5	IPC-A-600	Acceptability of Printed Boards
6	IPC-A-610	Acceptability of Electronic Components
7	IPC-7711/21	Rework and Repair of Electronic Components
8	J-STD-020	Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices
9	J-STD-033	MSD Moisture Sensitive Device Management Guidelines
10	IPC-9853	Hot Air Reflow Soldering System Characteristics and Verification Guidelines
11	IPC-7530	Guidelines for Temperature Profiles in Wave and Reflow Soldering
12	IPC-7351	Generic Requirements for Surface Mount Device and Land Pattern Design

• Terminology Abbreviations and Definitions

Abbreviations	Full Spelling	Chinese Explanation
ACF	Anisotropic Conductive Film	各向异性导电薄膜
AOI	Automated Optical Inspection	自动光学检测
BGA	Ball Grid Array	球栅阵列
BOM	Bill of Material	物料清单
Cmk	Capability Machine Index	设备能力指数
Cp	Process Capability Index	过程能力指数
Cpk	Process Capability Index	过程能力指数
CSP	Chip Size Package	芯片尺寸封装
CTE	Coefficient of Thermal Expansion	热膨胀系数
EMS	Electronic Manufacturing Services	电子专业制造服务
ENIG	Electroless Nickel and Immersion Gold	化镍浸金
EPA	Electrostatic Discharge Protected	静电放电保护工作区
ESD	Electrostatic Discharge	静电放电
FG	Fine Grain	细晶粒
FOV	Field of View	视场
FPC	Flexible Printed Circuit	柔性印刷电路板
GR&R	Gauge Repeatability & Reproducibility	可重复性与可再现性分析
HIC	Humidity Indicator Card	湿度指示卡
LED	Light Emitting Diode	发光二级管
LGA	Land Grid Array	栅格阵列封装
LSL	Lower Specification Limit	规格下限
MBB	Moisture Barrier Bag	防潮包装袋
MSDS	Material Safety Data Sheet	材料安全数据表
OSP	Organic Solderability Preservatives	有机可焊性保护涂层
PCB	Printed Circuit Board	印制电路板
PCBA	Printed Circuit Board Assembly	印制电路板组件
PCN	Process Correction Notification	流程更改通知
POP	Package on Package	叠层封装
QFN	Quad Flat No-Leads Package	方形扁平式无引脚封装
QFP	Quad Flat Package	四列引脚扁平封装
RCV	Receiver	听筒
RH	Relative Humidity	相对湿度
SAC	SnAgCu	锡银铜合金
SPK	Speaker	扬声器/喇叭
SMT	Surface Mount Technology	表面贴装技术
SOP	Small Outline Package	小外形封装
SOT	Small Outline Transistor	小外形晶体管
SPC	Statistical Process Control	工艺过程统计控制
SPI	Solder Printing Inspection	锡膏印刷检测
TDS	Technical Data Sheet	技术数据表
Tg	Glass-transition Temperature	玻璃化转变温度
USL	Upper Specification Limit	规格上限
WLCSP	Wafer Level Chip Size Package	晶圆级别芯片尺寸封装，即裸die芯片；厂家命名描述一般以“WL”开头，如WLNSP、WLPSP也属于此类器件。

Reference ArticleLink： Work Instruction SOP丨SPI Printing Inspection Work SOP

SPI Process Specification

1 SPI Inspection Requirements

Must configure online 3D SPI monitoring for solder paste printing quality.

Online SPI must have barcode scanning capability, SPI defect data must be saved for at least 3 months.

• Before starting process optimization on the printer, the following requirements should be met:

1. Solder paste must meet J-STD-005 or equivalent requirements.
2. The stencil should be in good condition and have the correct tension.
3. The squeegee blade/printing head should be in good condition and correctly installed.
4. During printing, there should be sufficient pin or fixture support for the PCB/FPC.
5. Both sides of the stencil and the inside of the openings should be clean (checked with a microscope).

2 SPI Equipment Capability Requirements

2.1 OnlineSPI Equipment Capability Requirements

Online SPI equipment must meet the general requirements in the table below. Level II requirements apply to products containing devices with 0.4mm pitch/0201 and above, while Level I requirements apply to products containing devices with 0.3/0.35mm pitch/01005 and above.

Reference ArticleLink： PCBA Manufacturing Process Specification: SPI Demo (Benchmark Selection) Evaluation Report

OnlineSPI Equipment Capability Requirements

No.	Item	TechnicalSpecifications	Specification Requirements
II Level Requirements	I Level Requirements
1	PCB Handling Capability	PCB measurable range (length×width)	50×50~450×535mm(single track) 50×50~450×250mm(double track)
PCB Thickness	0.4~4mm
PCB Warpage Automatic Compensation Amount	±5mm(the machine can automatically extend and retract)
PCB Weight	2.5KG
Panel Independent Detection Function	Can separately identify the mark points on the panel, preventing irregularities from causing mismeasurement
2	Precision Requirements	Barcode scanning (optional)	The camera can identify one-/two-dimensional barcodes; if a barcode is not read, parameters can be set to decide whether to continue testing
Camera	Resolution25um	Resolution20um
Minimum Measurement Size	Square: 200um Round: 250um	Square: 150um Round: 200um
Detection Capability	0201	01005
ZAxis Resolution	1pmbelow	0.6umbelow
HighPrecision	2pm
Volume Repeatability	<3%@3σ
Machine StabilityGR&R	Solder Paste Thickness Measurement≤10％ Solder Paste Area Measurement≤10％ Solder Paste Volume Measurement≤10％
3	Measurement Item Requirements	Excess solder, insufficient solder, bridging, pulling tips, poor shape	100% defect detection(according to testing principles)

2.2 SPI Equipment Programming Software System

Requires editing test applications using GERBER files to generate test files and allows for offline programming; SPC software must be able to output solder paste thickness, volume, area, solder paste 3D graphics, solder paste 2D graphics, X/Y offset graphics, thickness distribution statistics overlay graphics, CPK distribution, single-point SPC graphics.

3 Detection Frequency Requirements

3.1 OnlineSPI Detection Requirements

Every product produced online is inspected, and the solder paste quality CPK values are recorded every two hours.

4 Solder Paste Printing Specification Requirements

When conducting solder quality inspections, focus on detecting solder misalignment, solder paste volume, and solder paste area transfer rates according to the following requirements.

Reference ArticleLink：

PCBA Manufacturing Process Specification: FG Nano Printing Stencil Opening Area Ratio and Solder Paste Transfer Rate Relationship Study

4.1 Solder Misalignment Specification Requirements

01005 Component solder paste printing offset must be < standard pad’s30% of pad length and30% of pad width.

Non-01005 Components’ solder paste printing offset must be < standard pad’s35% of pad length and35% of pad width, or35% of pad diameter; if the solder paste printing offset exceeds the above requirements, realignment must be performed.Solder paste printing bridging must be realigned.

4.2 Solder Volume Specification Requirements

The solder volume and area must refer to the specifications in the table below; if exceeded, the PCB must be cleaned and solder parameters adjusted. Solder quality requirement Cpk≥1.33; prioritize solder paste volume transfer rate data.

Solder Volume and Area Specification Requirements Table

Stencil Theoretical Opening Area(Unit:mm2 )	A Class	B Class	C Class	D Class	E Class
0＜S≤0.05	0.05＜S≤ 0.1	0.1＜S≤0.5	0.5＜S≤1.5	S＞1.5
Volume Specification Limits (%)	LSL	25%	40%	40%	40%	40%
USL	150%	180%	200%	200%	200%
Area Specification Limits (%)	LSL	40%	40%	40%	60%	60%
USL	150%	180%	180%	200%	200%

Reference ArticleLink： PCBA Manufacturing Process Specification: SMT Solder Paste Usage Algorithm and SPI Parameter Setting Standards (Algorithm Formula)

Solder Thickness Warning Threshold Requirements Table

Stencil Thickness	Solder Paste Thickness LSL/um	Solder Paste Thickness USL/um
0.07mm	35	125
0.08mm	40	130
0.10mm	50	160
0.12mm	80	170
0.13mm	85	180
0.15mm	130	200
0.18mm	160	230
0.25mm	240	280
0.30mm	290	360

4.3 SPI Defect Handling Requirements

SPI defects can be handled according to the following requirements to reduce board washing; insufficient solder PCBA must not be directly reprinted on the solder surface, it must be cleaned thoroughly before use:

5 Process Alarm Control Requirements

Process Alarm Control Requirements
X bar Chart	If any point exceeds the upper control limit or falls below the lower control limit, an alarm will sound
R Range Chart	If any point exceeds the upper control line, an alarm will sound
Process Alarm Handling Methods	When the process engineer receives the SPC process alarm information, the process and equipment personnel should choose different handling methods based on the following abnormal conditions: False Alarm: Analyze the cause of the false alarm, optimize the testing procedure, and minimize the number of false alarms; Identified as Defect: Analyze the cause of the defect, provide avoidance measures to ensure normal production; Fill out the cause analysis and handling suggestions in the “CAR Production Issue Handling Form”.

5.1 GRR refers to the repeatability and reproducibility of measurements

5.2 Common Measurement Control Chart Comparison

Type	Name	Advantages	Disadvantages
X-R Chart	Mean / Range Control Chart	○ Easy to calculate ○ Can better estimate the process	Process estimation is worse than X-s Chart
X-R Chart	Median / Range Control Chart	○ Simple calculation	Process estimation is worse than X-R Chart
X-s Chart	Mean / Standard Deviation Control Chart	○ Most accurate for estimating the process	Complicated calculation
X-Rm Chart	Individual Value/Moving Range Control Chart	○ Simple calculation ○ Suitable for destructive, solvent density testing, or difficult measurements	Small sample size, least able to estimate the process
p Chart	Defective Rate Control Chart	○ Can be used with varying sample sizes ○ Can directly inspect defect rate trends	Control limits calculation is complicated, and each point must be calculated.
np Chart	Defect Number Control Chart	○ Used with constant sample sizes ○ Can directly inspect defect number trends	If deliberately specified the same sample size, it may cause missed defects.
u Chart	Unit Defect Count Control Chart	○ Can be used with varying sample sizes ○ Can directly inspect unit defect occurrence trends	Control limits calculation is complicated, and each point must be calculated.
c Chart	Defect Count Control Chart	○ Used with constant sample sizes ○ Can directly inspect defect occurrence trends	If deliberately specified the same sample size, it may cause missed defects.

5.3 Common SPC Control Techniques for SPI

• Mean Control Chart (X Bar Chart).

• Range Control Chart (R Chart)

• Standard Deviation Control Chart (S Chart).

• Process Capability Index, Cp

• Process Precision, Ca (or K)

• Process Comprehensive Capability Index, Cpk

5.4 Important Terminology Explanations

• Upper/Lower Specification Limits (USL/LSL)

• Upper/Lower Control Limits (UCL/LCL)

• Standard Deviation (Sigma)

• Process Capability Index-Cp

• Process Precision-Ca

• Process Comprehensive Capability Index-Cpk

Upper Specification Limit USL – The generated procedure is organized through the average values of various samples, according to statistical methods, to set the upper specification limit for shipment. (The same principle applies to the lower specification limit);

Upper Control Limit UCL – The generated procedure is based on sampling inspections of the product average values, plus the standard deviation of the distribution dispersion. SPI standard is 3 SIGMA;

Standard deviation is often used in probability statistics as a measure of statistical analysis (statistical dispersion);

In simple terms, standard deviation is a measurement concept of how much a set of values is dispersed from the average value. A larger standard deviation indicates that most values differ significantly from the average; a smaller standard deviation indicates that these values are closer to the average.

5.5 What is the best standard deviation

• Besides quality, cost is also a key consideration for the survival of enterprises

Defect Rate PPM Calculation: The number of defects produced in every million inspected samples

Sigma Level + – kσ	Cp Cpk	Yield %	Defect Rate ppm
1σ	0.33	68.27%	317,400
2σ	0.67	95.45%	45,600
3σ	1.00	99.73%	2,700
4σ	1.33	99.9937%	63
5σ	1.67	99.999943%	0.57
6σ	2.00	99.9999998%	0.002

5.5 How to Determine Cpk Quality

• The larger the Cpk value, the better the process capability

Grade Determination: Based on the size of the Cpk value, it can be divided into five levels

Level	Cpk Value	Handling Principles
A+	1.67 ≦ Cpk	No defects, consider reducing costs
A	1.33 ≦ Cpk ≦ 1.67	Maintain status quo
B	1 ≦ Cpk ≦ 1.33	Defects occur
C	0.67 ≦ Cpk ≦ 1	Immediate review and improvement
D	Cpk ≦ 0.67	Take emergency measures, improve quality, and discuss specifications

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