Get more benefit form COB technology in PCB Assembly fields

Get more benefit from COB technology in PCB Assembly fields

 

This article try to bring some ideas for the PCB designer who want to launch COB (Chip On Board) technology on the boards.

 

Firstly, we got more pressure from the end customer who need more competitive products and we might be seeking a new way to meet quickly change demand. COB technology  is really make a lower cost on the boards, it's cheaper way to use bare DIE's assembly boards compared the traditional surface mounted technology (SMT).  We know that Die's are more cheaper than a SOP pacakge parts. Secondly, we can design a smaller PCBs. That means we save PCB material cost at beginning. Thirdly, COB manufacturing process is very common in China. And thus we can get a cheap assembly cost.

 

How to make our own boards with COB technology? It's a better way to get some advice from PCB manufacturer and assembler. This can ensure our design achieve a very satisfied result.

 

Low cost COB technology is usually use FR4 base material and finish way on PCB is Ni plated, Gold plated, immersion gold. Note that H.A.S.L is not working here. We have to keep this in our mind. When we choose COB on our boards, a mixed SMT and COB process is recommended. Efficiency would be so perfect that we use COB and SMT process. PCB assembly manuacturer dislike COB and Through holes mixed process, cost will be higher than the formal way.

 

Some rules on COB PCB design

 

1, Gold wire's diameter is 20um~30um, so we have to make ball pad at least 2.5 times larger than gold wires. Making pad like a finger shape.

  

2, Power ring and ground ring is usually between Die's pin and Pads and make power ring and ground ring is coated with solder mask. Short circuit is big issue on process if we did not make good insulate on solder mask on this.

 

 

 

3, Dimention of finger's pad design

A	distance between finger pad
B	clearance of pad
C	width of finger pad
D	distance between finger and soler mask
E	minimum clearnce between finger pad and wire
F	minimum solder mask on Via
G	minimum distance between solder mask

 

4, Required dimension size for wire and bond width

 

 

 

 

5, Clearance distance ( B on figure4) between two finger pad should be big enough to keep short circuit issue. Usually the length of bond wire should be less than 5mm, and the recommended value is less than 100time diamter of wire( 100D).

 

 

 

 

6, Glue requirement on the chip when cover the Die.

 

7, Longest wirebond calculation

 

I hope information above can give you some idea when you design a COB boards. If you want to COB borads to be assembled, please contact me at info@onlitex.com . I am Mr.Allen Shieh from ONLITEX Electronic Co.

More information about ONLITEX please visit http://www.onlitex.com

 

I am planning to write more articles refer to PCB Assembly fields in the following days. Give me some time! ^_^

 

 

2009-12-06

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Allen Shieh - ONLITEX

ONLITEX Electronic Launch Kingdee K/3 ERP System on PCB Assembly manufacturing plant.

As a reliable PCBA supplier in small and middle volume manufacturing field, Onlitex Electronic updated MRP system to Kingdee K/3 ERP on October. Having a month trial of K/3 system, Onlitex Electronic launch the new ERP system to all department. The new system will help the company to bring more benefit for customer that need small and middle quantity PCB Assembly service. More efficient responsibility, more cost saving and stock management. This will give ONLIEX more capabilities to server the customer's vaviously requirement on low volume mamufacturing.

 

 

 

Onlitex Electronic release High brightness LED downlight.

Onlitex release one type of 305LM LED downlight this Monday. We are going to become one of reliable LED lighting fixture supplier in south of China. We are planing three new types of LED lighting product to the end of this year.

 

Model No. : GR3510CWK
Input Voltage: 85~265VAC  @ 50/60HZ
LED driver current: 350mA
LED Qty: 3pcs
Dimesion: 90x25mm
Luminous Flux: 305LM (102LM/W)
CRI: 75
Color: Cool White
Color Temp.: 6500K
-25C~65C
Operation Temp.: 15C~35C (degree)

Estimate price:  USD$9.9/pcs  (MOQ 500pcs)

Leadtime: 2 Weeks

For more information of this downlight, please email to sales@greelite.com  for details.

 

 

2009-08-18

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Allen Shieh - ONLITEX 

Conformal coating process in PCB Assembly manufacturing.

In PCBA fields , more and more boards need to be kept fromm humidity ,dusty and hight reliable insulation. So let go ahead to more information of conformal coating.

 

What's conformal coating?

 

Conformal coating is the process of spraying a dielectric material onto a device component to protect it from moisture, fungus, dust, corrosion, abrasion, and other environmental stresses. Common conformal coatings include silicone, acrylic, urethane, epoxy, and Parylene. Parylene is a unique polymer conformal coating that conforms to virtually any shape including crevices, points, sharp edges, and flat, exposed internal surfaces. Parylene is a higher level coating process. It used on high quality, reliable,precision requirement products,such as medical equipments. There are one professional supplier of parylene in China is Cookson , who located in Shanghai.

 

Three normal way to do conformal coating process

 

Brush coating works by flow coating the material onto the board and is suitable for low volume application, finishing and repair. The finish tends to be inferior cosmetically and can be subject to many defects such as bubbles. The coating also tends to be thicker and unless skilled operators used the coating, highly subjective in quality. And in this way you can add some fluorescent material to your coating liquid and when you work under a fluorescent lamp you can easily to find out which area or space is not covered the coating.

 

Spray application coating can be completed with a spray aerosol or dedicated spray booth with spray gun and is suitable for low and medium volume processing. The quality of the surface finish can be superior to all other methods when a trained skilled operator completes the process, as long as the circuit board is clean and the coating has no adhesion issues. The coating application may be limited due to 3D effects but masking requirements are more "shield" than "barrier" since the penetration is less effective. However, the lack of penetration can be an issue where coating is desired to penetrate under devices.

 

Conformal coating dipping is a highly repeatable process and if the PCB is designed correctly can be the highest volume technique. Coating penetrates everywhere, including under devices, and therefore any masking must be perfect to prevent leakage. Therefore, many PCBs are completely unsuitable for dipping due to desing. The issue of "thin tip coverage" where the material slumps around sharp edges can be a problem especially in a highly condensing atmosphere. This tip coverage effect can be eliminated by double dipping the PCB, using several thin layers of atomised spraying to achieve good coverage without exceeding coating thickness recommendations or a combination of the two techniques.

 

Conformal Coating Curing & Drying

Different Methods of curing / drying are available depending on the conformal coating material.Solvent & Water based conformal CoatingsFor standard solvent based acrylics, air drying (film forming) is the normal process except where speed is essential. Then accelerated heat curing can be used, using batch or inline ovens /conveyors and using typical cure profiles such as which are designed for max efficient curing without damage to the coating.Water based conformal coatings can be treated in the same manner but with more care with the application of the heat due to the slower drying times.

Onlitex Electronic Co., Ltd. who is one of OEM manufacturer can supply above three normal way conformal coating's supplier in south of China(Dongguan City, Guangdong Province). They provided low and medium volume quantity conformal coating service for around 4 years in the factory. You can get touch with them at following information.
Mr.Allen Shieh / Marketing Executive
Email: allen.shieh@onlitex.com
Web: http://www.onlitex.com