critical factors in thru hole defects - smtalp bottom side – surface temperature high! 150°c very...

Production needs us

Critical Factors in Thru Hole Defects

By Ernie Grice

Vice President of Sales

Kurtz Ersa North America

Production needs us

Soldering Zone

Seite 3 © by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013

Thru Hole Soldering Challenges


Small but deep Cut-outs are requiring a higher wave .

Effect: More turbulent wave with more dross creation.

Difficult to control the contact time => higher failure rate can be expected

Solution from Ersa: Programmable wave height in the solder program

.

7 mm !

Selective solder masks – High potential for defects!


Selectiv Solder Masks – lead free wave process !


Typical Thru Hole Defects:

• Bridging – Component Orientation, Lead Length, Pitch, Design

• Topside Hole Fill – Layer Count, Thermal Demand, Lead to Hole Ratio, Design

• Solder Balls – Flux and solder mask

• Insufficient Solder – Flux, Contamination

All of These factors can be resolved and more easily managed with Selective

Soldering.


Content Thermal Demand

• Fundamentals and the Physics of Solder Joints

• Thick Copper Technologies

• PCB Layout - Theory and Practice of Heat Traps

• Soldering defects

• Preheating Process

• Soldering Trials – Parameters and Results

• Conclusion


What is a “Good Quality” Joint?

Goal: 100% Through hole filling


Target conditions of the IPC A 610

Target – Class 1, 2, 3

There is 100% fill

This is easy to inspect, there is no

cause for any speculation


Acceptable conditions of the IPC A 610

Acceptable – Class 1, 2, 3

Minimum 75% fill

Question:

How to inspect 75% ??


Error Pattern – insufficient solder and possible consequences


„core“ – conditions at a solder joint to achieve „good quality“

Heat capacity


Glasübergangstemperatur TG

/734 F

/617 F

/644 F


Specification temperature of FR4 laminates versus process window

T288 TD

(320°C – 390°C)*

T300

Soldering: SAFE UNSAFE DESTRUCTIVE

* Depending on the specification

Resistance to Soldering Heat


Starting damage of PCB-laminate due to high solder temperature

Resin recession Delamination

Copper dissolution Delamination


If a solder joint requires

additional heat, the solder

temperature should be

increased incrementally and

very careful. At high solder

temperatures, copper leaches

very fast, in the worst case the

complete pad leaches into the

solder (see above).

Copper leaching

Increase wetting time before increasing solder temperature


Influence of the layout on the heat management of a solder joint

Capillary gap size Copper connected to the

plated through-hole

TTop > TM-Sol


Influences of the

PCB-Layout

on

soldering results


Selective Soldering by miniaturized solder waves

Heat transfer by flowing solder

within a limited area


Massive heat flow into Cu-layer

Energy transfer into a solder joint with 100% connection to a copper layer

FhG ISIT

ERSA


Reduced heat flow into Cu-layer

Energy transfer into a solder joint with heat trap present

FhG ISIT ERSA


Heat Traps and their Mode of Action on Printed Circuit Boards

Heat traps reduce the heat carrying cross section to those copper layers

attached to the joining location

Retaining the heat energy in the joining location is improved

The joining location heats up more quickly Desired Effect


Heat Traps - Layout recommendations


Insufficient usage of top side heaters

When the top side heaters can‘t transfer

sufficient energy to heat up the boards

top side, all the energy to heat up the

solder joint (PCB + pin) must be

transfered from the bottom side of the

assembly.

To ensure a rapid heat up of the solder

joint, thermal support vias transfer a large

amount of heat additionally to the PCB

top side.


Heat Traps for Busbars- Layout Recommendations

d1

d4

d3 d2

d1 ≤ d2 + d3 + d4

Dimension:

Please Note: The cross sectional area of the bus bar is reduced by

the drillings!

X

X

X

X


Layout recommendations

Thermal support vias to

improve the transfer of

heat up to the PCB top

side.

Heat traps to reduce

the heat flow into a

massive copper

layer. This layout is

recommended for all

layers of a PCB.

Reducing the heat capacity

of a busbar. Reducing the

diameter lowers the heat

flow from the pin into the

busbar.

Note that for all above layout recommendations, the current density

has always to be taken into consideration !


Layout – Capillary Action with Wave- and Selective Soldering

capillary gap

To increase the transfer of heat into the plated through-hole, it is recommended to

work on the upper limit of the capillary gap.

In power electronics the gap is 0,25 – 0,30 mm

Ratio of diameter pin – through-hole


Calculating the hole diameter for square pins

A

D

G

G

dH

A = pin dimension

D = A x √2

G = required for insertion

dH = D + (2 x G)


Possible Sources of Defects in the Selective Soldering Process

• Soldering System related

• Component related

Typical Error Pattern in Practice

• Non-Wetting

• Insufficient Capillary Rise

• Bridging

• Copper Leaching

• Pad- and/or Fillet Lifting

• SMDs Desoldered

Same Error Pattern!

Layout

Layout

Layout


• Selective soldering of thick copper PCBs with mini wave

systems is possible.

• The layout of the PCB plays of crucial role - especially the

connection of inner layers to THTs and the ratio of pin to hole

diameter.

• The specification of the PCB laminate has to be adapted to

the higher solder temperatures.

• The delamination temperature TD is especially critical !

• The more copper layers are in the board, the smaller will be

the process window for soldering.

Conclusion


The board layout has a large influence on the capillary rise and

the formation of bridges

The cause variables in the layout are

• Pad size / Contact spacing

• Pin length

• Plating of PTH joined to copper layers

• Size of capillary gap

• Distance between THT and SMD

Conclusion


The Process: Flux (F) – Preheat (PH) – Soldering (S)


FLUXING METHODS:

• Drop Jet Fluxer – Airless system. Precise Deposition. 2mm Dot Size.

Programmable Flux Amounts per joint. No Clean, Water Soluble and Rosin

Up to 15% solids.

• Ultrasonic Fluxer – Precise Deposition. Good for Spraying Rows. Good for

High Solids Rosin Fluxes.

• Spray Fluxer – Good for use of Chip Wave Style nozzle in selective.


Preheating: Top and Bottom


Preheating Multilayer Boards – Telecommunication (24 Layers)

T +++

T - - -

∆T

If, for multi-layer assemblies, thermal energy is supplied only from one side (lower side), then the heat has to travel, layer by layer, from the bottom up through the board. Since each layer absorbs energy, a temperature gradient exists from bottom to top of the board. Therefore, to achieve a uniform and homogeneous heating of the board, a correspondingly long time has to be accepted.


LP Bottom Side – Surface Temperature

IR Preheater only from

bottom side, with

maximum power (100%) !

Critical! 160°C

Long Preheat Time 140s

ΔT 30K

LP Top Side Temperature

Preheating: Multi-layer Boards with IR from bottom



High! 150°C

Very Long Preheat Time 190s

ΔT 20K


IR Preheater only from

bottom side, with reduced

power (66%) !

Preheating: Multi-layer Boards with IR from bottom


T +++

T +++

∆T

Preheating Multilayer Boards - Telecommunication (24 Layers)

If multi-layer boards are supplied with thermal energy from both sides, the heat penetrates the board simultaneously from top and from bottom. As a result, the temperature gradient is very small, and the board warms up uniformly and homogeneously at a much faster rate. At the same time, the stress experienced by the lower side is reduced, and the danger that the flux is damaged during the preheat process is minimized.


Preheating: Multi-layer Board with IR from bottom + convection from top


Not Critical! 140°C

Short Preheat Time 110s

ΔT 10K


Preheating from bottom

and from top, with reduced

power (65%) !


The use of Multijet Forced

Convection Optional Top

side pre-heating guarantees

a constant PCB temperature

during the entire selective

soldering process.

This guarantees that each

solder joint is made under

the same thermal conditions.

Highly recommended for

heavy, multilayer PCBs

which require a long process.

Forced Convection Top side pre-heating


Pot Temperature

Vo

idin

g

290280270260

10

5

0

Board

Thickness/Surface

Finish

1

2

Interaction Plot for Voiding

0 = Low Voiding (0% - 5%)

5 = Medium Voiding (5% - 10%)

10 = High Voiding ( >10%)

1 = .093" 106AX-HT OSP2 = .093" ImAg

Pot Temperature

Cu

Dis

so

luti

on

290280270260

10

5

0

Board

Thickness/Surface

Finish

1

2

Interaction Plot for Cu Dissolution

1 = .093" 106AX-HT OSP2 = .093" ImAg

0 = No Dissolution

5 = Slight Dissolution

10 = Total Dissolution

Pot TemperaturePot Temperature

Ho

le F

ill

290280270260

10

5

0

Board

Thickness/Surface

Finish

1

2

Interaction Plot for Hole Fill

1 = .093" 106AX-HT OSP

2 = .093" ImAg

0 = 0% - 25% Hole Fill

5 = 25% - 75% Hole Fill

10 = 75% - 100% Hole Fill

Copper Dissolution and The Need For Preheat

The more thermal energy you have in

your board, the lower your pot temperature

And dwell time can be in order to achieve a

Good solder joint. No preheat or not enough

Preheat warrants higher pot temps and

Higher dwell times in order to topside fill

On thermally challenging boards.


The Soldering Module: Things to Consider….

• Single Point or Multi-dip

• Moving Pot or Moving the Board

• Positional Accuracy of the Gantry

• Pumping Mechanism for Wave Height

• Dual Alloy Capable

• Fidicual Recognition

• Board Warpage Detection

• Nozzle Types and Sizes

• Nozzle Cleaning

• Keep out Areas


Multi-dip Single Point XYZ


Multi-Dip Tooling

Pros:

• Fast Cycle Times

Cons:

• Dedicated Tooling

• Change Over time

• Tooling Cost

• Universal Dwell time for all joints

• Requires Larger Keep out Area

• More N2 Consumption with Hood


Reflowlöten

Configuration - Single Solder Nozzle

- Constant solder flow over the complete nozzle surface – no preferred direction for solder to drain

- Continuous heat transfer into the solder joint during the solder process

- No orientation of the component to the solder nozzle required

- No layout constraints for the orientation of the components

- Suitable for a wide variety of solder alloys - Individual Wave Height and Dwell Time per Joint


Moving the Board or the Pot


Gripper Systems moves the entire PCB

with a gripper system, one PCB at a time.

Only Localized top side preheat possible. - moving only the solder

pot is 50% faster.

- no risk of vibration

during cooling.

- moving solder pot does not

require component fixing.

- top side preheating keeps PCB

temp. constant during soldering.

- a machine with segmented

process steps can handle up to 6 PCBs

at the same time!


A

B C

D

A D V A N T A G ES:

For soldering the square socket

just program a line and move the

solder nozzle from

A to B

B to C

C to D

D to A

and peel off It is not required to either turn

the board or the solder nozzle,

or to change any angles.

A recommended orientation of

the components is unnecessary


Repeatability is Critical


Reflowlöten

Design of Solder Bath

- Maintenance-free design with electro-magnetic solder pump

- No mechanical movable part in the solder bath - Precise wave height due to continuous circulation

of solder - Outstanding repeatability of solder process (no

impeller) - No adjustment after servicing the solder bath


Reflowlöten

Monitoring - Solder Bath

- Solder wave height is measured

- Solder level in bath is monitored / Solder wire feeder option

- Solder temperature is exactly controlled

- N2 atmosphere assures stabile process conditions

play video click button


Reflowlöten

Solder Module


Reflowlöten

Configuration Solder Module Z - variable

Variety of Alloys

- Both solder bath can be raised, separately and individually, on the axis up to the required working height (z- direction)

- Depiction of mode of operation with two identical nozzles but different alloys. - Depiction of mode of operation with two nozzles of different geometries and identical

solder.

Different nozzle geometries


Reflowlöten

- The distance of solder bath 1 to solder bath 2 can be adjusted on the axis system in the y-direction.

- Set-up for simultaneous soldering of two assemblies of a multi-up panel.

Configuration Solder Module Y- variable


Reflowlöten

Solder Snap-Off with Wettable Nozzle Surfaces

F1= Wetting Force F2= Capillary Force F3= Gravity F4= Adhesive Forces

- Solder snap-off, the point in the process when the solder breaks off from the solder joint, is positively assisted by the adhesive force F4, which is generated by the wettable surface of the nozzle.

- This adhesive force, in conjunction with gravity F3, enables the solder to properly drain off from the solder joint after having formed it, and to eliminate bridging and shorts.


Reflowlöten

Solder Snap-Off with Wettable Nozzle Surfaces

- forms convex solder joints

Standard Snap-Off

- forms concave solder joints

Controlled Snap-Off


Reflowlöten

Automatic Nozzle Activation:

• Automatic, preventive activation of the nozzle surface to prevent the surface from dewetting.

• The uniform wetting of the outer surface of the solder nozzles is essential for a stable process and constant soldering results.

• By a charging screw adipic powder will be applied on the solder nozzle in a specified interval.


Fiducial and Board Warpage

The need for fiducial Recognition and Board Warp Detection is highly

Dependent on the Assembly.


Pad Bohrung Pin

Scrap edge

3 mm

3 mm 6 mm

BE

Min. distance of a single solder point from the adjacent SMD pad or from the conveyor*


Off-centre positioning possibility of the solder wave


1 mm

Pad Through Hole Component

Minimum Distance of a multi-row connector to the adjacent SMD Pads*


Keep out area around dual and multi row solder joints (pitch 2.54 mm)*

Blue = Required keep out area

A = distance between pads ≥ 1 mm

B = distance between pads ≥ 2 mm

This recommendation should be used

for all double and multi row layouts,

starting with a pitch of > 2,54 mm.


X

keep out areas around selective solder joints

No keep out areas or solder

thieves required!


Programming Methods

• Joystick Teach :

• Pro – Easy to use

• Con- VERY Time consuming and Machine is not producing while

teaching, Requires live product

• Offline Programming:

• Pro – Machine runs production while programs created offline, Easy to

Use, Auto routing and cycle time calculations, CAD DXF or JPG, Very

Accurate!

• Con- Need Computer Knowledge

• Data Entry

• Pro- Can be done while machine is running

• Con- Requires hand measurements, VERY Time consuming.


• Scale Image

Result:

Scaled and rotated image


• 3D-View of Blocking Zones

Visual Monitoring due to 3D-View


• Optimized Line

• Optimized Cycel Times


• Multi Panel

• Profils can be easy duplicated

• Time optimized programming for multi panels


• Parameter-Set Up

Selection can be done in the graphic or in the Set-Data-List


Thank you for your attention!!!

We hope we can work with you for your soldering needs.

critical factors in thru hole defects - smtalp bottom side – surface temperature high! 150°c very...

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