1. I have to produce panels with 3/3 and 2/2 mils line and space imaging resolution. Do I need to use collimated or scattered light ?

2. What are the advantages and disadvantages of collimated light when working with solder-mask ?

3. What is the meaning of molecular diffusion ?

4. When to choose 5 or 8 kW lamp when using collimated light ?

5. What is the Automa-Tech ‘’Duck Mode‘’ ?

6. I hesitate to choose collimated light because this is more sensible to dust. What is your opinion ?

7. Automatic exposure units are not adapted to the needs of medium or small companies !

8. How do you guarantee an alignment accuracy of +/- 10 µm panel to artworks ?

9. What are the advantages of a double sided exposure, compared to a single sided one ?

10. How accurate is optical alignment with 4 CCD compared to the one obtained with 2 CCD cameras ?

11. What are the advantages of both artworks moving while maintaining the panel fix during alignment?

12. What does “tolerance of positioning +/- 12µm” mean ?

13. When is LDI a good choice for imaging ? Is LDI always a good choice for HDI product ?

14. What is the use of glass artworks ?




1. I have to produce panels with 3/3 and 2/2 mils line and space imaging resolution. Do I need to use collimated or scattered light ?

HDI process requires collimated light in order to reduce light diffusion. Light angle (declination + collimation) with a good collimated light source is typically less than 2° . With scattered light, the angle obtained is between 15° to 25° depending on the machines.

The diffusion value is the distance between the emulsion of artworks and the copper multiple tangent (light angle).
For example, with a dry film thickness (50µ) + Mylar thickness (25µ) = 75µ, the potential diffusion should be :

- 75µ * tan 20°= 27 µ with scattered light
- 75µ * tan 2° = 2.6µ with collimated light

This also shows that thinner dry film causes less diffusion.


2. What are the advantages and disadvantages of collimated light when working with solder mask ?

The only disadvantage is exposure time, because solder mask ink needs much more energy than dry film. However, there are solutions :

- Selection of ink : Most ink suppliers provide fully qualified solder mask inks requiring energy levels of 250 to 300 mJ

- Increase intensity Automa-Tech also proposes a high performance collimated light source 8 kW, with more than 50mJ/cm² average intensity for 18x24seconde’’ panel size. This means an exposure time of 5 to 6 seconds. There are many advantages to this solution.

- There may be gap between the emulsion and artworks, because of copper thickness deposits on the panel surface. This may cause diffusion, but it is minimal when using collimated light.

- This phenomenon also occurs in the case of surface irregularities, which can be more evident with multi layers.

- Due to irregularities of ink deposit less than 2µm in the angle of the conductor and 50µm at some other places, some areas are OVER exposed and other ones are UNDER exposed. Collimated light allows over exposure with less risks of diffusion (less molecular diffusion).


3. What is the meaning of molecular diffusion ?

Molecular diffusion occurs due to the penetration of light into photo sensible materials.
UV light transforms photo polymers. This one reflects one part of UV light. Thicker emulsion involves longer exposure and greater light reflection. Unfortunately this reflection is not only outside, but also inside emulsion. The result is also closely linked to the incidence angle of light.

The molecular diffusion is less sensible with collimated light than with scattered light.


4. When to choose 5 or 8 kW lanmp when using collimated light ?

The only resultant difference is exposure time.

If you use a standard dry film, requiring an energy level comprised between 30 and 70 mJ, a 5 kW lamp shall suffice. Exposure time will be 2 seconds or less.

If you use ink for primary image or solder mask with minimum required energy level of 250mJ, it may be recommended to work with a 8 kW lamp ; otherwise the exposure time may be excessive.


5. What is the Automa-Tech ‘’Duck Mode ‘’ ?

Automa-Tech’s unique dieset design of two fully independent frames supporting the artworks and their operation is referred to as the Duck Mode. There is no link between the upper frame (upper artwork) and the lower frame (lower artwork). Registration between both frames is achieved by means of employing 4 cones located at the 4 corners of each frame. This means there is no mechanical stress, as is the case with machines employing columns. The positioning with 4 cones is very accurate and repeatable during the machine life time. One frame side is first open, to break vacuum, then horizontal position, and frame is finally open. Thanks to this system, inner layers, for example, still remain at the right place on the lower glass after opening..

Another advantage is that glasses are not horizontally separated one from the other ; this eliminates risk of glass breaking due to vacuum and panels do not ‘’stick‘’ to the upper glass.


6. I hesitate to choose collimated light because this is more sensible to dust. What is your opinion ?

The question you have to answer first is : what kind of line and space you need to manufacture ?

Effectively, the quality of the definition obtained when working with collimated light involves an eventual dust particle to be imaged on the PCB.

Scattered light is less sensible to dust, because light diffusion is more important than dust size. This means you won’t obtain the right value of line and space, with the same diffusion. ‘’You can’t have your cake, and eat it.’’


7. Automatic exposure units are not adapted to the needs of medium or small companies !

It is difficult to calculate the cost for everyone, because each case is different ; but the main advantages are as follows :

- Repeatability of quality due to the process automatisation.

- The best possible artworks alignment, thanks to the use of optical process

- The very fast set up. With an automatic machine, the total set up time is less than 2 minutes (when the set of artworks is ready close the machine). The average time with a manual machine is 8 minutes. You save 6 minutes per batch, and so 7 hours of daily production if you manufacture 50 batches per day !

- You get an automatic production report per batch - And so on…


8. How do you guarantee an alignment accuracy of +/- 10 µm panel to artworks ?

All of the machine performances are listed by the ‘’Event Logging System.’’

All kinds of data are recorded for every panel (positioning before video alignment, result after video alignment, value after vacuum, energy on every side, glasses temperature before and after exposure, and so on…).

The ‘’Event Logging System” allows every panel to be easily controlled : data per panel, average per batch, trend, and so on… These results may be downloaded to any standard format. As our system is working under NT process, the machine can be connected to any PC, for an easy access to data.


9. What are the advantages of a double sided exposure, compared to a single sided one ?

The advantages are not the same, if you work with inner layers, external layers, solder mask, build up or conformal mask. Here are the one common to all processes :

- Automatic control of the dimension of upper artworks, in regards to the lower one, with possibility of stopping exposure if both dimensions are out of tolerance.

- Exposure of both sides with the same conditions.

- No possibility to reverse artworks ; the system controls assures that the upper artwork is installed on the upper glass and that the lower artwork is on the lower one.

- Smaller footprint for double sided exposure.

- Very small set up time : less than 2 minutes for the both sides. For Inner layers, it is the only way to guaranty the positioning of the image Top-to-Bottom Laser Via holes. It is the only system to simultaneously compensate laser drills on both sides, mechanical holes and reduce the ‘’Tower of Pisa effect’’ for double sided build up.


10. How accurate is optical alignment with 4 CCD compared to the one obtained with 2 CCD cameras ?

If all of the deformations were linear, the mathematical alignment result should be the same. But, in PCB activity, the deformation of base materials is not linear (due to surface preparation, brushing, humidity, drying, drilling dispersion,…).

A better average of all deformations is attained by considering 4 targets one in each corner of the panel. In these conditions, the alignment with 4 CCD cameras is always better than the one obtained with 2 CCD cameras, but this is directly linked to the deformation of base materials, and drilling dispersion.

Before choosing 4 or 2 CCD cameras you need to consider the panel size (larger panels require 4 CCD cameras) and the class difficulty of the product (the choice is not the same if you produce HDI product 2/2 mils L/S resolution or standard product 5/5 mils L/S resolution). Typically, more difficult or tighter tolerance jobs will require 4-point (4 CCD cameras) alignment.


11. What are the advantages of both artworks moving while maintaining the panel fix during alignment ?

Automa-Tech employs a patented process for aligning top and bottom artworks by moving these while maintaining the panel fixed. Conventional systems move the upper artwork and also move the panel. This latter method is less attractive since moving the panel requires :

- Drilling 2 holes in the panels and placing pins in these holes. This causes particulation from the holes to fall in the exposure area.

- Additional problems may arise when holes are completely or partially covered with dry film.

- The pins that are used to move panels are small flexible mechanical parts exhibiting spring effect which is not possible to suppress, resulting in reduced positioning accuracy.


12. What does “tolerance of positioning +/- 12µm” mean ?

Positioning tolerance is the performance of the machine to align perfect artworks and panels. The process is as follows :

- The system compares the position for every target of artworks and panels, by computing the error components in X-axis (dx) and Y-axis (dy) for each of them.

- Afterwards, the barycenter of all targets are compared to get the origin dx=0, dy=0 in the center of panels.

- The result is for 2 targets systems and not for dx and dy of the right target = -dx ,-dy (+/- 12µ) If artworks are 100µm bigger than the panel, the result on the panel near the target is not +/-12µm, but 50µm +/-12µ.


13. When is LDI a good choice for imaging ?

The LDI technology is perfectly adapted to production of prototypes, small-multiple batches and reworks, because there is no need for artworks. In these cases the pay back is rapidly obtained, even if purchasing and maintenance costs are more important than the ones of a standard automatic exposure unit. (We propose software to enter customer data and compute the break-even point).

Is LDI always a good choice for HDI product ?

- The resolution of LDI today is 2000 or 4000 dpi. With a good artwork plotting machine we reach 8 000, 12 000 or 24 000dpi. The reason is that we can spend half an hour to plot an artwork, but it is not economically feasible to spend half an hour to manufacture one side of a panel !

- Of course, there is no light diffusion with LDI, but the result is the same if you work with good collimated light. Recall that the laser beam is a collimated light. Avoid comparing with scattered light, this is not comparable !

- Generally, the dry film used for LDI is a 25µm dry film, with 10 mJ of energy. Low energy and thin dry film are 2 key parameters to limit the molecular diffusion. With any light source the result will be better than the one obtained with a 50µm dry film, 60mJ.

- Producing outer layers images with LDI allows the image to be adapted according to each panel deformation. This function is very attractive, but also very limiting, since it requires that the solder mask also be imaged with LDI. Otherwise, 4 or 5 set of artworks will be necessary to match the whole range of the panel.


14. What is the use of glass artworks ?

The only advantage is the stability of the mask with respect to temperature and humidity variations. The standard Mylar artwork is very sensible to humidity and temperature, for example :

- Temperature effect 16µ/°C/m with very small hysteresis effect.

- Humidity effect 8µ/%hr/m with important hysteresis effect. For example if your artworks are manufactured and stabilised in a room at 20°C and 45% RH and you use them at 24°C, 53%RH, for a 700mm artwork the possible deformation will be :
((24-20)*16+(53-45)*8)*0.7 = 128µ. Glass artworks are less sensible to temperature, and humidity has no effect.

- Temperature effect 4µ/°C/m

- The resulting Humidity effect for the same dimensions is : ((24-20)*4+(53-45)*0)*0.7 = 16µ 16µ versus 128µ.
This is the main reason for the use of glass artworks. On the other hand, the price of glass artworks is much higher. In most cases, working in a stable clean room, with good exposure units controlling glass temperature as the ones provided by Automa-Tech, provides a good solution and prevents the need for expensive glass artworks.