Seek advice on which steel/metal type to use for a press setup ...

[irpheus]

Hello Engineering Forums,

I will shortly be making a small press for PCB laminate fusing and to this end would appreciate a tip on which steel/"other material" type to use for the press' top and bottom plates. I've included a preliminary drawing of the press - hope it may give an idea about what I'm considering.

Some of the criteria for these steel/"other material" plates are:

- The steel/other material plate should bend as little as possible when pressing the PCB parts inside. When heated to 200 degr. celsius the bend deformation on the middle of the plates - relative to the sides where the tightening bolts are - should be less than 0.015 mm per plate, i.e. less than 0.03 mm for both plates. The plates should be able to press on the PCB parts with a pressure of 15 kg/cm2 with this deformation.

- The steel/other material plates must be able to transfer heat - i.e. not an insulator material.

- The steel/other material plate should not rust or corrode even when heated to 500 degr. celsius in a normal indoors environment. It's also fine if this may be achieved through some kind of surface treatment that does not affect the PCB parts inside.

- The steel/other material plate should be easily machinable

- The price for the plates should be quite reasonable - and the plates should also be readily available e.g in the UK (assuming that in this case such plates will also be available in Denmark).


I hope it is reasonably clear what I'm thinking of/what the criteria are for these two plates ... And to this end:

A.: May you have a suggestion as to which material would be feasible for these two plates? If altogether steel is preferred is there then a specific alloy that is best suited to this purpose?

B.: Which thickness of the plates would be sufficient? I'm considering 8- 15 mms (and I may calculate this, if necessary) but if you have an idea just off the bat that would be fine.

C.: Would it make sense to mount some structural braces on the top & bottom of the press - so as to increase stiffness and possibly reduce the thickness of the plates?

Well, if you got this far then thanks for reading & maybe also being able to give some feedback - I would appreciate your help in this ...

Cheers,

Jesper

 

[Maui]

I am unable to open your attachment, so I cannot see the geometry of the device. You did not list a hardness requirement for the plates. Your deflection criteria will need to be met based on the geometry of the plates. Thicker plates will deflect less under a given load. The overall requirements that you have listed for the plates suggest that you should start with a hot work tool steel that is tempered at a temperature above 1000F, such as H13. Surface treatments including nitriding and PVD coatings can be applied to H13 due to its relatively high tempering temperature. And in the United States it is relatively inexpensive when compared to other tool steels.

Maui

 

[irpheus]

Hi Maui,

& thanks for your feedback - I'll see if I can get H13 steel where I live here in Denmark (In case I cannot - may you suggest an alternative?).

Regarding the attachment I can open it myself - so don't know what happens .. ?? ... As a possible solution I have attached it again to this post with another file name - hope that solves it (it's a jpg file).

You did not list a hardness requirement for the plates.

No, you are right. I don't exactly know what it should be in practice, however, what is in the middle between the two plates is an appr. 0.3 mm thick re-inforced epoxy layer (PCB prepreg) and on both sides of this layer are e.g. 0.2 mm copper foils. So the hardest material in direct contact with the steel plates is copper. Would this change any of your recommendations?

Surface treatments including nitriding and PVD coatings can be applied to H13 due to its relatively high tempering temperature.

Is this something I would be able to apply myself or does it need/is best done by a professional?

Cheers,

Jesper

 

[EdStainless]

Normally these plates are not solid, but often more like waffle plates.
The thickness is what will limit the defection under load.
Do some basic bending beam calculations and see if you need to make it thicker.
Hardness, strength and such properties don't matter.
I like the idea of H13, or any tool steel designed for hot work. These materials will be more dimensionly stable when temperature cycled.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Maui]

Hi irpheus,

You're welcome. I was able to open the attachment in your second post. A typical hardness range for quenched and tempered H13 would be 45 - 50 Rockwell C. So quenched and tempered H13 will be more than hard enough for the application that you described. Make the plates as thick as your design will permit in order to minimize the deflections under load. You will not be able to perform nitriding or PVD coating yourself. It should be performed by a trained professional.

Maui

 

[arunmrao]

Maui,
Just a thought. In your next edition of the book, you could consider a chapter on " How to select materials". I find too often this question being posed in this forum, with very little inputs from the OP.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[irpheus]

Hi Maui & EdStainless,

Thank you both for your inputs.

@EdStainless:

The thickness is what will limit the defection under load.
Do some basic bending beam calculations and see if you need to make it thicker.

Uh ... it's been a long while since I've done this. Did it during my engineering studies but have almost entirely been focussed on electronics engineering since then - so although I recognise that it would be reasonable to do so maybe here I'll choose a bit of additional thickness as a short cut ...

@Maui:

You will not be able to perform nitriding or PVD coating yourself. It should be performed by a trained professional.

Ok - fine. I'll make an internet search to see where I can find this.

@arunmrao:

I find too often this question being posed in this forum, with very little inputs from the OP.

... Hmmm - although your comment is given to Maui - since you post your comment in this thread I will take the liberty to reply ... Knowing that I can only speak for myself here ... but IMHO one of the very fine qualities of a forum like this - and the help I have often received - is that I am able to get: 1. Almost instant & often very qualified help to a know-how "challenge" I may have. Something which may otherwise take many hours or days to clarify, 2. That the amount of "absorbing new knowledge" on my side is already huge so getting this help is indeed valuable, and 3. I wouldn't borrow/buy a specialized book to find out of this ... It takes too long to find out which book to order, ordering the book and also ... typically a book's treatment of its main topic is too comprehensive for my scope of finding out of this.

with very little inputs from the OP.

Well, not being a specialist in this field I may not assess if I've provided little input. But I always aim to give as balanced and sufficient input as I best can when I ask a question. So as to provide sufficient information while keeping the text not too long, and at the same time hoping/supporting that I get a useful reply - and ultimately do not "waste" the time of the people who reply. ... my thoughts on this ...

Cheers from Denmark

Jesper

 

[arunmrao]

irpheus,

The success of this forum is because members continue to actively contribute and share . Hope, you start sharing and participate more frequently rather than leach the forum.

Thanks.




"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[irpheus]

@arunmrao: Hmmm... there are times to go in and to stay out ... In this case I prefer to mainly stay out but just briefly say that although it is not obvious for me to contribute specifically to this forum (I'm not a materials specialist and am more likely to dilute matters) I aim to and do contribute in other contexts and in other ways.

I shall leave it here.

In neutrality,

Jesper

 

[arunmrao]

"pax vobiscum" : Peace be with you.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[mfgenggear]

question? how flat do these plates need to be?. something to consider, like double disk grind required after heat treat.

 

[Maui]

Arun, that is a good suggestion. The last chapter in my book [italic]Metallurgy for the Non-Metallurgist, Second Edition[/italic] is titled "The Materials Selection Process". It guides the reader through the process of choosing the right materials for their particular application.

Maui

 

[irpheus]

Hi mfgenggear,

Thank you also for your feedback ...

how flat do these plates need to be?. something to consider, like double disk grind required after heat treat.

A good question ... Basically as flat as practically possible, yet within "reason". Flatness is most important related to a constant impedance across the PCB, yet as I won't be making long traces nor entering into ultra-high frequencies I would say that around 0.01 to 0.015 mm across each of the plates. But I guess it also depends on what is realistic in terms of the plates? And if a grinding may allow for tighter tolerances ... I probably may have access to a metal workshop where they have a manual mill probably of a reasonable quality (I have not yet seen it) but I don't know what are realistic tolerances here?

Any experience here?

Cheers,

Jesper

 

[mfgenggear]

yes, milling can hold about .025 mm, for less than that I suggest surface grind, to hold .010 mm, surface grind can hold even less if the equipment is not worn.

 

[irpheus]

@mfgenggear: Thanks for the tip. Didn't know what surface grinding was but youtube was helpful here. Considering future possibilities I would aim for the 0.01 mm spec so I will look out for a place where surface grinding is available.

Thanks again ;-)

Jesper

 

[tbuelna]

For a high-temp-cured prepreg composite laminate you might consider Invar tool plates. Invar has a CTE similar to most composite fiber materials. Downside to Invar is cost, machinability, and low thermal conductivity.