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Impact of lead free simulated repeated reflow on through hole reliability using AATC

Multek

[email protected]

+49 171 463 5431

February 07, 2006

ABRACI

Sao Paulo

As of July 1, 2006, use of the following

substances in electrical and electronics

equipment sold in the EU is banned:

�Lead (Pb)

�Cadmium (Cd)

�Hexavalent Chromium (Cr+6)

�Mercury (Hg)�Poly Brominated Biphenyls (PBB)�Poly Brominated Di-Phenyl Ether (PBDE)

RoHS Directive 2002/95/EC January 27 2003

Lead Free Requirements – Reflow @ 260 C

• Conveyor speed used to reach 260°C on the board surface: 28 inch/min.

• Rising slope from ambient temperature to 200°C: 0.7°C/s.

• Rising time between 25°C and 200°C: 302 seconds.

• Time above 217°C: 73 seconds.

• Mean peak temperature on surface: 257.9°C.

• Following are the oven temperatures per zone:

1. 100°C

2. 120°C

3. 140°C

4. 160°C

5. 180°C

6. 200°C

7. 215°C

8. 260°C

9. 285°C 10. 290°C

T 260 C PeakTypical Profile

Must: 5 xWant: 7-9 x2 x reflow1 x wave1-3 x rework

High Temperature Solder Reflow

Unknowns

�Via reliability (via cracking)?

�De-Lamination Resistance ?

�De Composition Resistance?

�Electrical Degradation?

�Other potential latent defects??

Typical Lead Free Assembly Requirements

Significant more stress on

the PCB during PCB

assembly and repair

(potentially multiple times)

Study objective

Objectives:

� Understand the impact of simulated lead free repeated reflow on through hole reliability and its failure modes and understand the importance of the material properties

� CTE

� Tg

� Curing mechanism

� Verify test methodology with “small” number of materials to discriminate materials for LF suitability

Project Scope

Variables

Materials:

� Isola FR 402

�Polyclad PCL 254

� Isola IS 400

� Isola IS 410

Process:

�Simulated Lead Free Repeated Reflow (Convection Reflow Oven)

� 2, 4, 5, 6 times at 250 C conditioning before thermal cycling

Measured Response

�Decrease in Through Hole Life Expectation (probability plots)

Test Vehicle / Test Procedure

120 mil (3.2 mm) thick (8 samples / condition min)12 mil (0.3 mm) drill diameter 10 : 1 Aspect Ratio8 layers880 Plated Through Holes (PTH)Target copper metallization (0.8 mil = 20 µm thickness) No finishBase Laminates:

�Isola FR402 (low Tg, dicy cured and unfilled)�Polyclad PCL-FR-254 (mid-Tg, Dicy cured and filled)�Isola IS400 (mid-Tg, Phenolic cured and filled resin)�Isola IS410 (high-Tg, Phenolic cured and unfilled)

Test Conditions:�5 min @ -55°C�14 min transition time�5 min @ 125°C�14 min transition time

Failure criterion: 10% resistance increase of the initial value

Tested Materials

340

13 / 16

> 10 s

n/a

45

280

155

PCL 254

Dicy Cured

300

14 / 17

>10 s

2

52

321

130 - 135

FR 402

Dicy Cured

340 - 360340 - 360Td (C)

17 / 15 (fill)

13 / 6 (warp)

15 / 12 (fill)

12 / 5 (warp)

x/y( PPM)

expansion

30 min10 minT288 (min)

6060 T260 (min)

55

217

38

200

Z – axis <Tg

PPM >Tg

170 – 180145 - 150Tg (C)

IS 410

Phenolic C.

IS 400

Phenolic C.

Material

Properties

Filled Filled

Influence of Reflow Temperature on

PTH Reliability

224 C Peak vs. 250 C Peak for 5 simulated cycles

Results: Influence of reflow temperature

Isola IS 410

5 x reflow

Isola IS 400

5 x reflow


Polyclad PCL-

FR 254

5 x reflow


All tested materials

5 x reflow

An increase of 25°C

in reflow temperature simulated 5 x

reduces reliability by about 25 %


Influence of number of simulated reflow

cycles on PTH reliability

224 C Peak vs. 250 C Peak

2 , 4, 5, 6 simulated reflow cycles

IS 410

250°C reflow

Results: Influence of number of reflow cycles

2456

All tested materials

224°C reflow


Increasing numberof reflow cycles reduce the through-

hole reliability, more at higher temperatures.

2456

All materialstested250°C reflow

Increasing numberof reflow cycles reduces the through-hole reliability. More

at higher temperatures


2456

Influence of laminate type on PTH

reliability

224 C Peak vs. 250 C Peak

2 and 6 simulated reflow cycles

IS 410, IS 400, PCL 254

2 x reflow

224°C and 250°C peak temp.

Results: Influence of base material

IS 400

IS 410

PCL 254

6 x reflow,

224°C and 250°C peak temp.


IS 400

IS 410

PCL 254

All pre-conditioning TBoth peak T

IS 400 (mid Tg, phenolic

cured, filled) shows thebest through hole reliabilityof the investigated materials.


IS 400

IS 410

PCL 254

Comparison Dicy Curing vs. Phenolic Curing

5x reflow

224 and 250°C

peak temp.

STD

MNF1

HN

MNF2

5x reflow

224 and 250°C

peak temp.

FR 402

PCL 254

IS 410

IS 400

Dicy Cured Phenolic Cured

Material Properties (measured)

Tg, TMACTE (z)

below Tg

CTE (z)

above Tg

°C ppm/K ppm/K 20 - 250°C

FR 402 130 - 135 67 321 44240

P- 254 150 - 155 67 315 40210

IS 400 145 - 150 57 293 37890IS 410 170 - 180 73 285 33750

Lowest CTE valueHighest CTE value

z-axis-expansion

ppm

Comment

Dicy Cured

Dicy Cured Filled

PC - Filled

Phenolic Cured

FAILURE ANALYSIS

BARREL CRACKS

FR 402 5x reflow at 250°CFailed after 51 cycles.Failure mode: Barrel cracking

Results: Influence of unused pads

FR4025x reflow at 250°CFailed after 99 cycles.Failure mode: Barrel cracking

Results: Influence of unused pads

IS4006 x reflow 250°C peak TFailed after 1096 cycles

Failure mode: Barrel cracking

Results: Failure Modes

IS 4102 x reflow with 250°C peak TFailed after 516 cycles Failure mode: Barrel cracking


PCL 254After 2 x reflow 250°C peak TFailed after 478 cycles Failure mode: Barrel cracking


AATC - Summary

�An increase of ~ 25°C in reflow temperature decreases through hole reliability roughly by about 25%.(at 5 x reflow)

�Increasing number of reflow cycles reduces the through hole reliability.

�Material ranking IS 400 �IS 410 � PCL 254 � FR 402�Phenolic Filled, Phenolic, Dicy Filled, Dicy

�Tg is NOT the most critical factor for reliability & Lead Free Material Selection�Low z axes expansion (filled materials) can serve efficiently

�Predominant failure mode observed has been barrel cracking (what we want to see)

�AATC tests have been suitable for further material benchmarking and ranking (although time consuming)

�Plan is to test further materials against the tested 4

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