Adaptive Intelligenz beim Schablonendruck mit 3D Post Print Inspektion

Adaptive Intelligenz beim Schablonendruck

mit 3D Post Print Inspektion

Technologie und Ausblicke für die Baugruppenfertigung im 21ten Jahrhundert Erik Jung

Fraunhofer IZM Gustav-Meyer-Allee 25

D-13355 Berlin Email: erju@izm.fhg.de

Overview

•Motivation •AOI

•Technology of FP

•Adaptive Process Control •Summary

Motivation: Future of SMT stencil printing in the 21st century

-higher performance requirements -lower cost requirements

-higher quality requirements

Development projects targeting the limits of current stencil print technology

-ultrafine pitch SMD printing for miniature solder volume (e.g. 0201 components) -Flip chip and CSP bumping

Cooperation with EKRA within bilateral and public funded projects

Projekt: Ökobump – Ökologisches/Ökonomisches Bumping für die MST

Projektziele • Erarbeitung einer

Bumpingtechnologie die eine ökomisch attraktive Alternative für den Einsatz in der Mikrosystemtechnik zu teuren Verfahren darstellt

• Erarbeitung einer Bumpingtechnologie, die die Erfordernisse einer nachhaltigen, umweltsensitiven Fertigung nachkommt

Quality Control – Distribution of Rejects

Machines and Processes 40% Materials 11% Design 14% Setup/Execution 35%

Quality Control – Influentials and Cost of Quality

Chart 0 5 10 15 20 25 3 4 5 6 7

Sigma Level Levels Options Percentage of Revenue Loss

Processing related defect account for

~ 86% of quality loss!

Defect source distribution for SMT assembly*

Process control, σ-level

SMT - Process Flow

Defect Distribution

-Screen

Print

Pick &

Place

Reflow

Through-hole

population

Wave

Test

Electr. / Funct.

SMT - Process Related Defects in %

New and old problems...

Components shrinkage...now at 0201 Component number steadily increasing

Solder paste deposits smaller in size and higher in number

Wafer Bumping challenges with minute solder deposits and huge numbers Printed resistors, printed interconnects, .... Open new fields of application

Screen

Print

Pick &

Place

Reflow

Through-hole

population

Wave

Test

Electr. / Funct.

•

inspection of monitor structures on PCB (100%)

•

inspection of selected structures on PCB (100%)

•

inspection of complete PCB (100%)

•

random inspection of complete PCB

Can be done using manual or automated means

Product

How to adress stencil print related defects

General Requirement in Production:

no increase of the cycle time,

this would mean production loss!

Screen

Print

Pick &

Place

Reflow

Through-hole

population

Wave

Test

Electr. / Funct.

•

100 % process control using AOI

•

feeding back the information into the

process using trend analysis tools

•

Online monitoring of the printing quality

•

Online control of the printing process

Product

Parameters to be controlled....

Print position

Print area (2D)

Print height (3D)

Print volume (extracted from 2D and 3D)

Print shape (extrapolating to n+1st print)

Missing prints

Optical Inspection

Avoidance of Defects during Printing by Operator

Printer

AOI

Observer, i.e. machine operator ? (Print_n- Print _n-1) = ? ?(actual -nominal) < 0 Comparator (D_n - D_n-1) Paste Stencil Temp/Humid Parameter Boards ?(actual -nominal) ≥ 0 Data acquisition P₁ P₂ . . . P_n Software Actors

Subjective analysis of sampled AOI results based on experience of individual operator

Subjective trend analysis based on individual experience

Example of Wafer Bumping

Device under

Test

Feed back the

results

Process Variations allow a

trend analysis

No way to have an operator assisted

by a AOI equipment to evaluate print

Printer

P & P

AOI

Solution: Closed Loop Process Control with well informed observer

Comparation Print (D_n-Dt_n-1) ? (Dr_n- Dr_n-1) > 0 ? (Actual -Nominal) < 0 ≤ 0 Analysis Print Identification Print Result/Parameter Help on decision of corrective actions Machine paramters Paste parameters Paste Stencil Temp./Humidity Print Parameter Boards Squeegee Parameter Cleaning Stencil

Actual / Nominal Comparation

Software ?( actual -nominal) ≥ 0 Parameter Analysis P₁ P₂ . . P_n Actors Data acquisition Courtesy: EKRA

AOI Objectives

ü

High speed AOI system with feed back

possibility

ü

Ultra fast imaging system

ü

Stencil teach-in dedicated to ease-of-use

ü

Closed loop algorithms btw. AOI results and

printing parameters (printer adaption

possibilities required!)

AOI technolgies available

B/w camera to check parts of the board or total board

Color cameras to check parts of the board or total board

Mixed technologies b/w camera, color illumination

Projected fringe method (moiré method)

Laser scanning methods

** many methods are optimized for post assembly inspection** ** interface and technology do not lend themselves easily

Inspection Speed

Inspection depth and resolution should be adapted to

the actual requirements in order to minimize process

time and maximize printing quality

•High Resolution Mode

•High Speed mode

Camera Camera

Stereo Vision

One data point per pad

Camera Laser

Laser Triangulation

One scanned profile per pass

Camera Projecteur FMI Fringe Projection, e.g. FMI™ Full 3D measures, more than 300 points

per pad

Comparison of technologies

AOI principle using Fringe Projection Methods

Projecting fringes from one direction and detecting

the distorted fringes from another side allows 3D imaging of a contoured surface.

Full image vs. scanning technology

• Commercialized as FMI = Fast Moiré Interferometry

• Uses a combination of Projector/Camera

• Projector displays grid on to substrate

• Camera grabs image

• Grid movement and camera acquisitions are

performed a total of 4 times

• 3-D image is built from multiple distorted fringe

images

• Software algorithms analyze and process images

• Very fast: 11 seconds on medium density PCB 12 X8

(300x200mm)

AOI using projected fringes

High Resolution Telecentric

Standard CCD Camera

FMI Projector with telecentric

projection optics

Grid Projection

Substrate Inspected

FMI™ Technology

Step1:

(Image A,B,C,D)

4 images are acquired one after the

other while the grid moves and projects

a pattern on the component. Projector

moves in

Step2:

( Phase Image E)

From those 4 images, a 3D phase

Image is generated with the algorithms.

A

B

C

D

E

3D image

Fringe Projection Steps

Step3:

(Image F)

A fifth image is acquired for 2D

information

Step4:

(Image E,F)

Finally, 3D and 2D measurements are

obtained using both images ‘E’ and ‘F’

images.

Note: The processing of data to acquire

measurements is done in parallel with the image acquisition

.

F

2D image

Measurements from E and F

Fringe Projection Steps

FMI Grid Projection

FMI Live Image

Reconstructed 2D Image

3D Phase Image

Z Resolution Calculation

Considering a 10-bit CCD Camera H = Height Order (150u)

( H )

210 = 0.025µm

½π

Camera Resolution

Physical Resolution

- depends on projected fringe -typical x/y resolution ~5um -typical z resolution ~1um

Surface Height Measurement at Each Pixel! (Voxels)

Holes, Voids etc..

• Teach-in system scans the stencil to determine

location of components and critical print data

– Actual stencil thickness (=> determine target height)

– Actual aperture size (=>determine target volume and pad

coverage)

– Pitch of apertures and keep-out area (=>determine risk of

shorts and critical areas)

• The combination of above information gives a

unbiased picture of what high quality results should

look like

Defects identified – and what then...

Three strategies currently used:

1) Adjust process parameters according to process knowledge 2) Stop process and verify setup, parameters, material

3) Auto-adjust process parameters within predefined limits according to process knowledge

All have advantages and disadvantages:

1) Fastest line of action during process setup and small volume production

non repeatable flow of action, dependent on the skill of the operator

2) Increase time consumption for correction action, increase line downtime,

always known good process, also well suitable for manual documentation

3) Minimize time comsumption due to allowance of the equipment to act autonomously,

change in process parameters must be documented electronically by the equipment,

process must be well understood if no additional defects are to be produced =>versed operator/ expert system

AOI AOI Measure- Measure-ment ment Misaligned stencil Adjust screen printer Adjust printer Bad stencil or boards Measure stencil & boards

Clean stencil & board

Excess paste Collect 3D data Inspect stencil Damaged

apertures

Inspect stencil Volume High Contamination at board/stencil interface

Clean stencil & board

Poor handling Warped stencil Paste on back of

stencil

Height High Inspect stencil Snap-off height too high Squeegee speed too fast Dried paste on stencil apertures

Clean stencil Paste temp too high

Paste volume on printer too low

Add fresh paste Paste has absorbed moisture Squeegee speed

too fast

Adjust printer Warped stencil Inspect stencil

Volume Low Polymer blades scoop out paste Squeegee speed too fast

Adjust printer Separation control speed too fast Squeegee speed too fast

Adjust printer Adjust printer

Large Height Variation

Table 1 - Defects caused during screen printing require automated optical inspection measurements and suggest different causes and actions.

Possible Cause Action Action

Paste to Pad Offset

Bridge

Smear Clean stencil

Slump Low Area

High Area Poor aperture gasketing due to excessive squeegee pressure, debris on board, or damaged Possible Cause

Courtesy: Burr, Donald, "Printing Guidelines for BGA and CSP Assemblies,„ SMI 1998, pp. 417-424.

Understanding the influencing factors in stencil printing

Corrective actions either by versed operator or by expert system

0 1 2 3 4 5 0,00 0,05 0,10 0,15 0,20 Printed Height (125µm) Print Speed

Understanding the influencing factors in stencil printing

Stencil: contaminated openings lead to defects

high surface contamination deteriorate print result Paste: viscosity changes deteriorate print results

separation deteriorates print results

Print and clean parameters allow to keep the printing results in the desired range

Other factors that cannot be controlled by the printing process, e.g. substrate warpage, solder mask opening, ...

Control of printing parameters

Best control is excerted when using closed printheads that not only controll print speed and blade pressure but allow a much better control over all relevant parameters

All leading manufacturers provide closed printhead systems: e.g. EKRA: Crossflow

Fuji: no specific name MPM: Rheometric Pump DEK: Proflow

pressure sensor

Actuators with paste level indicator

material chamber inside

Standard SEMCO cartridges

e.g. EKRA CROSSFLOW

Closed Squeegee System

PID proportional valve controlle d system pressure sensor

Pressure setting output

Piston

new development

§ easy to use like standard squeegee

§ closed loop real time pressure control

§ decoupling of paste pressure from squeegee head pressure

ð paste pressure setting

ð down force setting

§ homogenous paste pressure

§ independence of material properties

§ hermetically sealed

§ material waste reduction

Close up of the printhead

• To close the loop between AOI results and printer

actions in real time

• Application algorithm is critical to response

determination

=>Software examines high speed AOI results according

to expert (system) trend analysis and initiates

responses directly in the printer within the allowed

process limits

EKRA Adaptive Intelligence (EAI)

EKRA Adaptive Intelligence (EAI)

Reactions

are based on predetermined Range/ Limits/

Trendanalysis Results: Built-in process understanding

•

Wiper functions

– clears stencil before defects occur

•

Stencil Inspection

– addresses particular aperture (e.g.

monitor apertures) or full stencil

•

Pressure

– fine tune to adapt to material changes

•

Offsets

– board stretch based on 2D/X-Y position

•

Stop

– stops machine if problem requires manual

intervention, signalling to operator if autonomy limits are

reached.

Examples of various applications

Bumped Die

CSP, BGA