Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Printed Circuit Board Material

NLykus

#2766

Printed Circuit Board Material | 11 October, 2000

Does anyone have any experience with running a double sided/surface mount(bottom)board manufactured with CHEM 1 material?

We are currently looking at cost cuts. My personal experience recently in running a D.O.E. against other materials and solder masks, the CHEM 1 material bowed and twisted dramatically in the wave. The other board materials tested under same conditions worked very well. Board stack up layer counts, copper content,and scoring was the same on all boards tested.

Boards were all run the same. No fixturing was used. (fingers)

Does anyone know why the CHEM 1 bombed big time?

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#2767

Re: Printed Circuit Board Material | 13 October, 2000

Talk more about your CEM board fabrication and assembly processes, please.

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NLykus

#2768

Re: Printed Circuit Board Material | 16 October, 2000

CEM 1 is a laminate base board material. The other boards in the experiment were manufactured using FR4 as the base board material. What I'm leaning towards is that the glass transition temperature "Tg". What do you think?

Topside temperatures in the wave experiments ranged from 99oC to 110oC. All boards had a previous heat cyle prior to wave for a glue cure (125oC for 3 minutes).

If you have any suggestions, please advise. Thanks, Nance

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#2769

Re: Printed Circuit Board Material | 16 October, 2000

Thanks Nance.

So, your production process is: * Screen / dispense glue on secondary side * Place secondary side SMT components * Cure glue * Insert primary side PTH components * Wave secondary side

Please tell us about: * Flux type and wave solder temperature * Locations, weight, layers, and PTH plating and thickness of the boards.

What do you mean when you say: "What I'm leaning towards is that the glass transition temperature �Tg�."

Two things: 1 Is it that you are thinking that there is a range of materials with properties between CEM-1 and FR-4. 2 Boat loads of CEM-1 is soldered every day

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NLykus

#2770

Re: Printed Circuit Board Material | 17 October, 2000

Dave, Current process is Insert through hole components topside Dispense SMT glue Place SMT components bottom side Glue cure Insert 1 through hole component by hand Wave

Wave temperature is 480oF Topside preheats in D.O.E ranged from 99oc to 108oC Flux type VOC No clean water based Board layer count 1 Copper content 1 oz. SMOBC/HASL (single sided) Board thickness .062 - .067" Score lines .018 - .022" deep both sides Board dimensions 7.25" X 5.750"

As I mentioned before, the only differences in the boards were solder mask type and the Cem 1 material. Results from the DOE were very dramatic. The Cem 1 material had twice the amount of insuffients compared to the other boards. When I mentioned the glass transition temperature, I'm looking for suggestions as to what caused this dramatically different results.

Thanks for your help.

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#2771

Re: Printed Circuit Board Material | 18 October, 2000

It's unrealistic to think that two materials with the following disperant properties would have the same reflow profile.

From http://www.norplex.com/Carrier.htm

Physical Properties / NEMA FR-4 / NEMA CEM-1 Glass transition temperature �C / 130 / 100 Flexural Strength - psi / 70,000 x 60,000 / 48,000 x 40,000 Flexural Modulus - psi x 106 / 2.5 x 2.3 / 2.2 x 2.0 Moisture Absorption - % / 0.15 / 0.25 Compressive Strength - psi / 55,000 / 50,000 Shear Strength - psi / 22,000 / 12,500 Coefficient of Thermal Expansion - ppm / 10 x 12 / 13 x 16 Flammability - UL94 / V-0 / V-0

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NLykus

#2772

Re: Printed Circuit Board Material | 19 October, 2000

Great information. Your all right in my book "Dave F".

Thanks for your help. Will redesign D.O.E. with more refined profiles for the different materials and let you know how it goes.

Take care

N. Lykus

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