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

Multek

Helmut.Kroener@de.multek.com

+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

Results: Influence of reflow temperature

Polyclad PCL-

FR 254

5 x reflow

Results: Influence of reflow temperature

All tested materials

5 x reflow

An increase of 25°C

in reflow temperature simulated 5 x

reduces reliability by about 25 %

Results: Influence of reflow temperature

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

Results: Influence of number of reflow cycles

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

Results: Influence of number of reflow cycles

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.

Results: Influence of base material

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.

Results: Influence of base material

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

Results: Failure Modes

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

Results: Failure Modes

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